WO2014047704A1 - Method for preparing super-hydrophobic nanomembranes and product - Google Patents

Method for preparing super-hydrophobic nanomembranes and product Download PDF

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Publication number
WO2014047704A1
WO2014047704A1 PCT/BR2013/000368 BR2013000368W WO2014047704A1 WO 2014047704 A1 WO2014047704 A1 WO 2014047704A1 BR 2013000368 W BR2013000368 W BR 2013000368W WO 2014047704 A1 WO2014047704 A1 WO 2014047704A1
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superhydrophobic
nanomembranes
water
nanoparticles
hydrophobic
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PCT/BR2013/000368
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French (fr)
Portuguese (pt)
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Antonio FERREIRA ÁVILA
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Universidade Federal De Minas Gerais - Ufmg
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    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
    • D01F6/02—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D01F6/20—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polymers of cyclic compounds with one carbon-to-carbon double bond in the side chain
    • D01F6/22—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polymers of cyclic compounds with one carbon-to-carbon double bond in the side chain from polystyrene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
    • B05D5/08—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/20—Compounding polymers with additives, e.g. colouring
    • C08J3/205—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase
    • C08J3/21—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase the polymer being premixed with a liquid phase
    • C08J3/212—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase the polymer being premixed with a liquid phase and solid additives
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/0007—Electro-spinning
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F1/00—General methods for the manufacture of artificial filaments or the like
    • D01F1/02—Addition of substances to the spinning solution or to the melt
    • D01F1/10—Other agents for modifying properties
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
    • D04H1/72—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged
    • D04H1/728—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged by electro-spinning
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2601/00—Inorganic fillers
    • B05D2601/20—Inorganic fillers used for non-pigmentation effect
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2325/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Derivatives of such polymers
    • C08J2325/02—Homopolymers or copolymers of hydrocarbons
    • C08J2325/04—Homopolymers or copolymers of styrene
    • C08J2325/06—Polystyrene

Definitions

  • the treated material consists of superhydrophobic nanomembranes obtained by electrofinning polymer solutions, preferably polystyrene (PS), previously dissolved in an organic solvent or one. mixture of organic solvents and impregnated with one of the following nanoparticles: zinc sulfide, cadmium sulfide, nanosilic or graphene. These nanomembranes are mainly applied as surface sealers and as antifreeze.
  • the nanomembranes formed after the addition of the above mentioned nanoparticles are superhydrophobic structures, where the contact angles with water (CA) are greater than 150 °.
  • CA contact angles with water
  • superhydrophobic nanomembranes interact very little with water, preventing water or moisture from settling and freezing on surfaces such as appliances, objects or machines. For this reason, superhydrophobic nanomembranes can be applied to waterproofing fabrics and upholstery, anti-fog systems for car windshields, buses, airplanes, glasses and as anti-freeze systems for refrigeration equipment, aircraft surfaces
  • Gao and Rose the drop in aircraft performance due to ice build-up on wings or control surfaces is a major concern in the aviation industry.
  • a thin layer of ice on the wing of an airplane can disrupt airflow and therefore cause loss of altitude, increased drag, increased fuel consumption and degradation of control systems that may eventually lead to an accident (Gao, H; Rose, JL Ice Detection and Classification on an Aircraft Wing with Ultrasonic Shear Horizontal Guided Waves. IEEE Transactions on Ultrasonics, Ferroelectric and Frequency Contro! , 334-344, 2009).
  • Some aircraft defrosting techniques involve the use of chemical-based defrost fluids, such as ethylene glycol or propylene glycol.
  • a common strategy for improving the performance of such defrost fluids is the addition of different ingredients such as thickening surfactants, anti-corrosive agents and UV sensitive dyes.
  • These "modified" defrost fluids perform well when applied to aircraft wings and control surfaces, even under atmospheric conditions. adverse. The good results, however, are masked by the thaw fluids toxicity. Thawing fluid toxicity is an environmental concern, and researchers are trying to find less toxic alternatives (ie non-glycol based alternatives).
  • a superhydrophobic surface is the only one that can completely repel water droplets; Such surfaces have water contact angles (AC) of 150 ° or greater.
  • AC water contact angles
  • Tourkine and colleagues pointed out that superhydrophobic coatings can also delay freezing as there is generally a thin layer of air trapped beneath the surface of the surface of the surface of the water, which forms a trapped surface. may provide a thermal barrier between solid and liquid (Tourkine, P. et al. Delayed Freezing on Water Repellent Materials. Langmuir, 7214-7216, 2009).
  • Shang and colleagues nanostructured materials can also generate hydrophobic surfaces.
  • Shang's work involved a huge surface area containing nanostructured materials that showed increased roughness and, consequently, hydrophobicity (Shang, H.M. et al. Nanostructured Superhydrophobic Surfaces. Journal of Materials Science, 3587-3591, 2005.)
  • PTFE polytetrafluoroethylene
  • the "forest” of PTFE-coated carbon nanotubes has a water contact angle of around 161 °; and a 5% increase in contact angle was obtained when the PTFE coating was applied.
  • Lau's work did not establish a relationship between the density of compacted carbon nanotubes and the hydrophobicity phenomenon (Lau, KKS et al. "Superhydrophobic Carbon Nanotube Forest. Nano Letters, 1701-1705, 2003)
  • Jin and colleagues created a "Gecko-like" nanostructure based on a porous nanoscale model that allows the formation of a strongly dense area of polystyrene nanotubes. This nanostructure had a superhydrophobic surface with water contact angle (CA) around 162 °.
  • CA water contact angle
  • the main disadvantage of Jin's work is the complexity of manufacturing (Jin, M. et al. Superhydrophobic Aligned Polystyrene Nanotube Film with High Adhesive Force. Advanced Materials, 17 (6): 1977-1981, 2005).
  • Kang et al. Also used electroporation and polystyrene, but with different operating parameters. Considering a much higher matrix / solvent ratio, this figure reached 35% while in Jiang's article this value was limited to 25%. Kang obtained a more uniform set of nanofibers. The water AC, however, reached the maximum value of 154 °. This limitation is due to nanofiber diameters and morphology that may be influenced by different solvents used, such as chloroform (CHCl 3 ), ⁇ , ⁇ '-dimethylformamide (DMF) and tetrahydrofuran (THF) and their flow ratios (KANG). , M. et al., Preparation of Superhydrophobic Polystyrene Membranes by Electrospinning, Colloids and Surfaces A. Physicochemistry Engineering Aspects, 313-314 (2), 41 1-41, 2008).
  • CHCl 3 chloroform
  • DMF ⁇ , ⁇ '-dimethylformamide
  • THF
  • Miyauchi and colleagues described the process of obtaining a super-hydrophobic self-cleaning membrane based on a 30% polystyrene solution at varying DM F / TH rates F - 4/0, 3/1, 2/2 , 1/3 and 0/4, respectively. After solubilization of the polymer, the mixture was exposed to the electrophony technique. The obtained material presented AC higher than 159.5 °, which characterizes the superhydrophobicity of the membrane. However, the nanofibers obtained by the use of DM F / PS were not completely homogeneous, with formation of PS microspheres which limits their superhydrophobicity character.
  • US2002150723 entitled “Suraces which are self-cleaning by hydrophobic structures, and a process for their production” describes the process of obtaining micrometric hydrophobic structures from the use of polymers, including polystyrene, for the production of surfaces with “self-cleaning” characteristics.
  • polymers including polystyrene
  • hydrophobic substances such as wax, oil, among others.
  • the material obtained was not superhydrophobic and did not have antifreeze properties.
  • Patent Application KR201 10059173 entitled "Superhydrophobic coating composition, using the same, and method of manufacturing thereof” describes the process of obtaining superhydrophobic coating compositions by depositing graphene oxide on the structure of a hydrophobic polymer. containing fluoride and can be used as a self-cleaning and antifouling coating. This technology, however, uses the graphene weight percentage from 3.0% to 30%, which differs from the present application, which is 0.5%. In addition, the superhydrophobic film obtained from the above patent application has no antifreeze properties.
  • EP2484431 describes the process of obtaining hydrophobic nanomembranes by using a mixture of at least two types of lipophilic polymers selected from the group of the following: Polymers: polystyrene, polyethylene, polyurethane, nylon, polyacrylonitrile, polymethyl methacrylate, polyvinyl chloride, dissolved in organic solvents and exposed to electrophilization technique to obtain hydrophobic nanometric fibers.
  • said technology requires a plasma treatment to check the hydrophobicity in the nanomembrane and yet the nanomembrane obtained is not superhydrophobic.
  • Patent Application KR746643 entitled "Method for producing superhydrophobic fibrous membrane by electrospinning a solution prepared by dissolving polystyrene into a non-volatile solvent, and superhydrophobic fibrous membrane produced by the method” describes the process of obtaining a superhydrophobic polymeric membrane to From a hydrophobic polymer, polystyrene, dissolved in DMF organic solvent to be electrophilized.
  • the above document reports the use of polystyrene only to obtain the superhydrophobic membrane, and the contact angle with water. (CA) obtained is about 150 °.
  • the concentration range of PS used was between 30 and 40% in parts by weight and the obtained membrane has no use as an efficient antifreeze system.
  • Patent application PI0903844 entitled “Method and apparatus for producing micro and / or nanofiber blankets from polymers, their uses and coating methods” describes a process for obtaining nano and micro fibers from a group of polymers between them.
  • polystyrene previously dissolved in an organic solvent, which may be charged with organic particles such as carbon nanofibers or inorganic, for example, ZnO.
  • organic particles such as carbon nanofibers or inorganic, for example, ZnO.
  • high speed air jets are used.
  • this hydrophobic membrane is mainly limited to waterproofing: cleaning utensils, in impervious clothing and protective against biological and chemical agents, not being usable as a barrier for freezing.
  • the nanomembrane production process proposed in the present application generates superhydrophobic polystyrene nanomembranes with AC values above 150 ° provide excellent resistance to adhesion or interaction of water with the surface covered by the nanomembrane.
  • the superhydrophobic nanomembranes obtained also have antifreeze properties, among others.
  • Figure 02 shows the water contact angle (AC) values for all nine experiment groups.
  • Figure 03 shows the scanning electron microscopy image
  • Figure 05 shows a high magnification microscopy (SEM) image of the surface of the PS / DMF nanomembrane highlighting its roughness.
  • Figure 06 shows the image of a drop of water on PS / DM F / graphene nanofibers.
  • Figure 07 shows a microscopic (SEM) image of the PS / DMF / graphene nanomembrane.
  • Figure 08 shows a high magnification microscopy (SEM) image of the PS / DMF / graphene nanofiber roughness.
  • Figure 09 shows a microscopic (SEM) image of a water droplet "sitting" in nanosilic bundles on the PS / DMF / nanosilic nanomembrane.
  • Figure 10 shows the nanofibers obtained by dispersing nanosilicide to the PS / DMF solution.
  • Figure 11 shows a high magnification microscopy (SEM) image of the rough surface of PS / DMF / nanosilum with encrusted nanosilic particles.
  • Figure 12 shows the image of a drop of water on the surface of the PS / DMF / CdS nanomembrane.
  • Figure 13 shows a microscopic (SEM) image of PS / DMF / CdS nanofibers with some cadmium sulfide clusters (bright white particles) that can be seen between the fibers.
  • Figure 14 shows the roughness of a PS nanofiber. / DM F / CdS where polystyrene nanofiber partially covers the CdS.
  • Figure 15 shows the microscopic (SEM) image of the 5.0% w / w PS / DMF / ZnS nanomembrane.
  • Figure 16 shows a microscopic (SEM) image of the 10.0% w / w PS / DMF / ZnS nanomembrane.
  • Figure 17 shows a microscopic (SEM) image of the 15.0% w / w PS / DMF / ZnS nanomembrane.
  • Figure 18 shows a drop of water on the nanomembrane surface obtained from Group 09.
  • Figure 19 shows the values for surface energy, considering the Neumann model for each set of membranes tested.
  • Figure 20 shows a drop of liquid water at -7 ° C situated on the nanomembranes.
  • the superhydrophobic nanomembranes, objects of the present invention, are obtained by the electrophony technique.
  • This technique allows the preparation of fibers of nanometric diameters, ranging from 1.37 to 4.13 ⁇ by applying an electric field between the polymer / solvent solution and the target substrate.
  • Polymer / solvent solutions have concentrations ranging from 20 to 35% w / w polymer and are prepared by adding the polymer to the solvent under constant stirring at 200 rpm and heating at 40 ° C.
  • the solution is then cooled to room temperature (between 20 and 25 ° C). Then the nanoparticles are added separately to the solution and the solution is sonicated.
  • the electrophony technique used to obtain nanomembranes is a considerably efficient, fast and inexpensive process in the manufacture of nanometer and / or micrometer sized materials.
  • the electrophony equipment used to obtain the nanomembranes is basically composed of a high voltage source, an infusion pump, a stainless steel capillary tube and a rotary cylinder.
  • the polymer / solvent / nanoparticle solution is inserted into the electrophony apparatus through a small inlet (metal hole) and subjected to an electrical potential difference from a collecting target, also metallic.
  • the solvent is separated from the polymer as the mixture is ejected, thus forming nanometric fibers that deposit on the bulkhead / substrate.
  • the process is controlled by the electric field established (kept constant in this case) by the infusion pump and the fluid viscosity.
  • the collecting target represents the metallic bulkhead where the mesh composed of formed fibers is collected during the process. Upon completion of the process, this membrane is placed on an aluminum surface.
  • the solvents that may be used in the process are selected from the group comprising carbon tetrachloride, chloroform, dimethyl sulfoxide (DMSO), hexane, toluene, benzene, preferably dimethylformamide (DMF) or tetrahydrofuran (THF).
  • polyurethane PU
  • PEO ethylene polyoxide
  • PET polyethylene terephthalate
  • PVDF vinylidene polyfluoride
  • PS polystyrene
  • the superhydrophobic materials obtained in the present invention in the form of membranes or films are nanofibers woven as a type of "skin" by the technique of electrophony from a polymer, preferably PS.
  • Nanomembrane thicknesses may vary depending on the type of nanoparticles used, which may be metallic or non-metallic.
  • Nanoparticles used as doping agents to obtain superhydrophobic nanomembranes added to the polymer / solvent solution comprise graphene, nanosilium, cadmium sulfide (CdS) and zinc sulfide (ZnS). It is noteworthy that graphene was obtained according to the process described by ⁇ vila and colleagues ( ⁇ vila, A.F. et al. Composites. Part B, 41 (2), 380-387, 2010). The concentrations of the nanoparticle solutions employed ranged from 0.1 to 20.0%, preferably 0.5% w / w graphene, 0.5 to 1.0% w / w nanosilica, 5.0% CdS, and 10 to 15% w / w ZnS.
  • Figure 20 shows a drop of water in liquid form at -7 ° C situated on the doped nanomembranes containing 15% w / w ZnS. Due to the superhydrophobicity of the membrane obtained, the interaction of the water droplet with the surface becomes insignificant, thus preventing water from freezing and becoming embedded in the surface.
  • This invention may be better understood by the following non-limiting examples.
  • PS 190,000 g / mol
  • DMF organic solvent
  • a concentration between 35% by weight as the upper limit and 20% by weight as the lower limit was chosen.
  • the nanoparticle (zinc sulfide, cadmium sulfide, graphene or nanosilic) is added.
  • a sonicator was used at a frequency of 20 KHz for a period ranging from 30 to 60 minutes.
  • the electrophony apparatus used consists of a high voltage supplier, an infusion pump, a stainless steel capillary tube and a rotary cylinder.
  • the flow rate used was set at 17 to 33 pL / min at an applied voltage of 15 KV.
  • the density of the applied electric field was
  • nanofiber morphology was investigated by scanning electron microscope. The images were processed by software. Changes in nanomembrane morphology after doping with different nanoparticles already referenced were evaluated by measuring viscosity.
  • group 01 the proportion of 20 wt% polystyrene and 80 wt% DMF was used.
  • group 02 35 wt% polystyrene and 65 wt% DMF were used.
  • the ratio 20 wt% PS and 80 wt% DMF were used.
  • the exfoliated graphene was added in the proportion of 0.5% by mass, in order to avoid the increase of nanomembrane viscosity.
  • the ratio 20 wt% PS and 80 wt% DMF were used.
  • the exfoliated nanosilicide was added at 0.5 wt% for group 04 and 1.0 wt% for group 05.
  • the ratio 20 wt% PS and 80 wt% DMF, and 5.0 wt% CdS were used.
  • the ratio 20 wt% PS and 80 wt% DMF were used.
  • the proportions of 5.0 wt% ZnS were added for group 07, 10% and 15 wt% ZnS respectively for groups 08 and 09.
  • Table 1 summarizes each set of experiments performed and the main parameter with regard to the process of electroporation.
  • the electric field density applied to the electrophony technique was kept constant and equal to 150 KV / m in all nine sets of experiments.
  • Table 1 also shows the reagent concentrations and their flow rates.
  • Figure 1 shows the dynamic viscosity values for each set of experiments performed. As can be seen, with increasing rotation (high shear rates), the dynamic viscosity decreases. However, as commented by Guerrini et al., During shear processes low shear rates are developed due to reduced flow rate (Guerrini, LM et al. Electrospinning and Characterization of Polyamide 66 Nanofibers with Different Molecular Weights. Materials Research, 181 -190, 2009). Thus, as the dynamic viscosity value for group 02 is higher than those of the other groups, its flow rate has been increased to maintain the same electrostatic force in all cases. The same flow rate was used for group 01 for comparison purposes. EXAMPLE 3 - Investigation of the influence of morphology and hydrophobicity of polystyrene nanomembranes by the addition of nanoparticles (Groups 01 to 09)
  • the Scanning Optical Microscopy (SEM) image for group 01 shows scattered fibers in a random orientation.
  • Such orientation means that there are many places where air can be trapped, which can lead to hydrophobicity considering the Cassie model. According to Carré, this is due to the low surface energy of PS (CARRÉ, A. Polar Interactions at Liquid / Polymer Interfaces. J. Adhes. Sci. Tech, 21 (10): 961-981, 2007).
  • the water contact angle of (144 ⁇ 4) ° can be explained by a Cassie and Wenzel, as it seems almost impossible for a drop of water to be completely "sitting" under an air bubble.
  • the percentage by weight of nanosilic used was 0.5% for group 04 and 1.0% by weight for group 05.
  • the contact angle of water (AC) obtained was (149.79 ⁇ 7.85). ° for group 04 and (153.09 ⁇ 6.58) ° for group 05.
  • CA values There is a slight decrease in CA values when compared to graphene samples, but higher than PS / DMF solution without addition of the nanoparticle.
  • Figure 9 shows the drop of water "sitting" on bundles of nanosilica fibers. This superhydrophobic surface is the result of a double fold process.
  • Cadmium sulfide (CdS) at 5 wt% was dispersed in the PS / DMF solution.
  • the same electrocirculation operating parameters were applied, however the flow rate was about 1.0 mLVh, half of the previous ones.
  • the water contact angle for the PS / DMF / CdS surface was (152 ⁇ 7) °, very close to that measured for the PS / DM F / nanosilicon surface.
  • Figure 12 shows the drop of water "fitted" to this superhydrophobic surface. Although the contact angle of the water was almost the same, the drop of water in this case was 2.0 ml. Also, according to Lafuma and Quowski, (2003) larger drops of water can be flattened by gravity. A possible explanation for the presence of large spherical water droplets is the existence of nanofibers around the base of the water droplet. This hypothesis can be corroborated by observations in SEM microscopy.
  • the additional increase in CA for groups 08 and 09 may be due to agglomeration of Zn nanoparticles through the walls of PS nanofibers.
  • These agglomerates are of the order of (378.92 ⁇ 8.78) nm for the addition of 10% w / w ZnS (group 08) and (561.31 ⁇ 11.94) nm for the addition of 15% w / w ZnS (group 09), respectively.
  • the roughness obtained on the fiber surface becomes larger and consequently a higher CA value is obtained.
  • Figure 18 shows a drop of water on the surface from group 09.
  • the surface tension of an aluminum surface is about 1,100 MJ / m 2 , four orders of magnitude higher than that of group 09, which was about 0.03 MJ / m 2 . m 2 (Garcia-Cordiovilla, C. et al. The Surface Tension of Liquid Pure Aluminum and Aluminum-Magnesium Alloy. Journal of Materials Science, 2787-2792, 1986).

Abstract

The present subject matter consists in super-hydrophobic nanomembranes produced by electrospinning polymer solutions, preferably polystyrene (PS), previously dissolved in an organic solvent or in a mixture of organic solvents and impregnated with one of the following nanoparticles: zinc sulphide, cadmium sulphide, nanosilica or graphene. These nanomembranes are mainly used as surface water-proofing agents and as anti-freezing agents. The nanomembranes formed by admixture of the above-mentioned nanoparticles are super-hydrophobic structures with water contact angles (CA) of more than 150°. Thus, the super-hydrophobic nanomembranes hardly react with water, preventing water or moisture from depositing and freezing on surfaces such as appliances, objects or machines. For this reason, the super-hydrophobic nanomembranes can be used for water-proofing textiles and upholsteries, in anti-fogging agents for automobile windshields, in buses, airplanes, spectacles, and as anti-freezing systems for refrigeration equipment, airplane surfaces and high-voltage cables, inter alia.

Description

"Processo de preparação de nanomembranas super-hidrofóbicas e  "Process for the preparation of superhydrophobic nanomembranes and
produto"  product"
A matéria tratada consiste em nanomembranas super-hidrofóbicas obtidas por eletrofiação de soluções de polímeros, preferencialmente o poliestireno (PS), previamente dissolvidos em um solvente orgânico ou em uma . mistura de solventes orgânicos e impregnado com uma das seguintes nanopartículas: sulfeto de zinco, sulfeto de cádmio, nanosílica ou grafeno. Essas nanomembranas são aplicadas, principalmente, como impermeabilizantes de superfícies e como anti-congelante. As nanomembranas formadas após a adição das nanopartículas supracitadas são estruturas super- hidrofóbicas, onde os ângulos de contato com a água (CA) são superiores a 150°. Assim, as nanomembranas super-hidrofóbicas interagem muito pouco com a água, evitando com que a água ou umidade se depositem e congelem em superfícies como, por exemplo, de aparelhos, objetos ou máquinas. Por esse motivo, as nanomembranas super-hidrofóbicas podem ser aplicadas na impermeabilização de tecidos e estofados, em sistemas anti-embaçantes para para-brisas de automóveis, em ônibus, em aviões, em óculos e como sistemas anti-congelamento para equipamentos de refrigeração, superfícies de aeronaves e fios de alta tensão, não limitante. The treated material consists of superhydrophobic nanomembranes obtained by electrofinning polymer solutions, preferably polystyrene (PS), previously dissolved in an organic solvent or one. mixture of organic solvents and impregnated with one of the following nanoparticles: zinc sulfide, cadmium sulfide, nanosilic or graphene. These nanomembranes are mainly applied as surface sealers and as antifreeze. The nanomembranes formed after the addition of the above mentioned nanoparticles are superhydrophobic structures, where the contact angles with water (CA) are greater than 150 °. Thus, superhydrophobic nanomembranes interact very little with water, preventing water or moisture from settling and freezing on surfaces such as appliances, objects or machines. For this reason, superhydrophobic nanomembranes can be applied to waterproofing fabrics and upholstery, anti-fog systems for car windshields, buses, airplanes, glasses and as anti-freeze systems for refrigeration equipment, aircraft surfaces and non-limiting high voltage wires.
Como discutido por Kulinich e Farzaneh, a adesão de gelo e neve molhada em superfícies externas é reconhecida como causas de graves problemas para linhas de transmissão de energia, embarcações e aeronaves (Kulinich, S.A; Farzanesh, M. On Ice-releasing Properties of Rough Hydrophobic Coatings. Cold Regions Science and Technology, 60-64, 201 1 ).  As discussed by Kulinich and Farzaneh, adhesion of wet ice and snow to external surfaces is recognized as causing serious problems for power transmission lines, vessels and aircraft (Kulinich, SA; Farzanesh, M. On Ice-releasing Properties of Rough Hydrophobic Coatings, Cold Regions Science and Technology, 60-64, 2011).
De acordo com Gao e Rose, a queda no desempenho dos aviões devido ao acúmulo de gelo nas asas ou superfícies de controle é uma grande preocupação na indústria aeronáutica. Uma fina camada de gelo sobre a asa de um avião pode perturbar o fluxo de ar e, consequentemente, ser a causa da perda de altitude, aumento do arrastar, aumento do consumo de combustível e da degradação de sistemas de controle que, eventualmente, podem levar a um acidente (Gao, H; Rose, J.L. Ice Detection and Classification on an Aircraft Wing with Ultrasonic Shear Horizontal Guided Waves. IEEE Transactions on Ultrasonics, Ferroelectric and Frequency Contro! , 334-344, 2009). According to Gao and Rose, the drop in aircraft performance due to ice build-up on wings or control surfaces is a major concern in the aviation industry. A thin layer of ice on the wing of an airplane can disrupt airflow and therefore cause loss of altitude, increased drag, increased fuel consumption and degradation of control systems that may eventually lead to an accident (Gao, H; Rose, JL Ice Detection and Classification on an Aircraft Wing with Ultrasonic Shear Horizontal Guided Waves. IEEE Transactions on Ultrasonics, Ferroelectric and Frequency Contro! , 334-344, 2009).
Como mencionado por Bragg e colaboradores, entre 1997 e 1988, houveram 803 acidentes relacionados com o gelo na aviação com muitas mortes (Bragg, M.B. An Interdisciplinary Approach to Inflight Aircraft Icing Safety. Aerospace Sciences Meeting & Exhibit, 36, AIAA, Washington, DC, . 1 - 15, 1998). Em 1992, devido a preocupações de segurança, a Federal Aviation Administration (FAA) emitiu o seguinte regulamento: "Os pilotos que operam em condições de gelo devem verificar se há formação de gelo antes da decolagem". Há muitas formas possíveis de remover o gelo e a neve das asas e superfícies de controle de aeronaves.  As mentioned by Bragg and colleagues, between 1997 and 1988 there were 803 aviation-related ice-related accidents with many deaths (Bragg, MB An Interdisciplinary Approach to Inflight Aircraft Icing Safety. Aerospace Sciences Meeting & Exhibit, 36, AIAA, Washington, DC 1 - 15, 1998). In 1992, due to safety concerns, the Federal Aviation Administration (FAA) issued the following regulation: "Pilots operating in icy conditions should check for ice formation prior to takeoff." There are many possible ways to remove ice and snow from aircraft wings and control surfaces.
De acordo com Menini e colaboradores, as estratégias utilizadas para lidar com o acúmulo de gelo e/ou de neve podem ser divididas em duas categorias diferentes: métodos ativos de degelo como técnicas térmicas, mecânicas ou elétricas, e métodos passivos como revestimentos de proteção. Sistemas termais de placas de aquecimento por resistência haviam sido propostos como dispositivos de degelo/anti-congelamento para aeronaves desde o início dos anos 1940s. No entanto, esses dispositivos tiveram aplicações limitadas devido ao alto consumo de energia e/ou restrições por razões aerodinâmicas. Por outro lado, os revestimentos de proteção têm a intenção de reduzir a força de adesão do gelo a substratos. Além disso, estes revestimentos "gelofóbicos" são, em geral, superfícies super-hidrofóbicas ou hidrofóbicas (Menini, R. et al. Highly Resistant Icephobic Coatings on Aluminum Alloys. Cold Regions Science and Technology, 65-69, 20 ).  According to Menini et al., The strategies used to deal with the accumulation of ice and / or snow can be divided into two different categories: active defrosting methods such as thermal, mechanical or electrical techniques, and passive methods such as protective coatings. Thermal resistance plate heating systems had been proposed as defrost / freeze devices for aircraft since the early 1940s. However, these devices have had limited applications due to high power consumption and / or restrictions for aerodynamic reasons. On the other hand, protective coatings are intended to reduce the bond strength of ice to substrates. In addition, these "gelophobic" coatings are generally superhydrophobic or hydrophobic surfaces (Menini, R. et al. Highly Resistant Icephobic Coatings on Aluminum Alloys. Cold Regions Science and Technology, 65-69, 20).
Como descrito por LaForte e colaboradores, algumas técnicas de degelo para aeronaves envolvem o uso dos fluidos de degelo que são à base de produtos químicos, como por exemplo, etilenoglicol ou propilenoglicol. Uma estratégia comum para melhorar o desempenho de tais fluidos de degelo é a adição de diferentes ingredientes como agentes tensoativos de espessamento, agentes anti-corrosivos e corantes sensíveis a UV. Estes fluidos de degelo "modificados" exibem bons resultados quando aplicados às asas e às superfícies de controle de aviões, mesmo sob condições atmosféricas adversas. Os bons resultados, no entanto, são mascarados pela toxicidade dos fluidos de degelo. A toxicidade de fluidos de degelo é uma preocupação ambiental, e os pesquisadores estão tentando encontrar alternativas menos tóxicas (ou seja, alternativas que não sejam à base de glicol). Outras estratégias podem ser utilizadas para minimizar o impacto ambiental, tais como o recolhimento dos fluidos usados e utilização da diluição máxima compatível com a segurança (Laforte, J.P. et al. A Facility to Evaluate Performance of Aircraft Ground de/anti-icing Fluids Subjected to Freezing Rain. Cold Regions Science and Technology, 161 -171 , 1990) . As described by LaForte et al., Some aircraft defrosting techniques involve the use of chemical-based defrost fluids, such as ethylene glycol or propylene glycol. A common strategy for improving the performance of such defrost fluids is the addition of different ingredients such as thickening surfactants, anti-corrosive agents and UV sensitive dyes. These "modified" defrost fluids perform well when applied to aircraft wings and control surfaces, even under atmospheric conditions. adverse. The good results, however, are masked by the thaw fluids toxicity. Thawing fluid toxicity is an environmental concern, and researchers are trying to find less toxic alternatives (ie non-glycol based alternatives). Other strategies can be used to minimize environmental impact, such as the collection of used fluids and the use of the maximum safety-compatible dilution (Laforte, JP et al. The Anti-icing Fluids Subjected to Freezing Rain, Cold Regions Science and Technology, 161-171, 1990).
Mais recentemente, Menini e colaboradores também atentaram para os chamados revestimentos "gelofóbicos". Segundo eles, estes revestimentos são mais ecológicos, quando comparados com os fluidos de degelo e apresentam menor custo do queos métodos ativos (que consomem muita energia) os demais métodosque possuem alto custo de manufatura e operação.  More recently, Menini and colleagues have also looked at so-called "gelophobic" coatings. According to them, these coatings are more environmentally friendly when compared to the defrost fluids and are cheaper than the active methods (which consume a lot of energy) and the other methods that have a high cost of manufacture and operation.
Conforme comentado por Kulinich e Farzaneh , existe uma correlação entre o comportamento "gelofóbico" e superfícies super-hidrofóbicas. A força de adesão do gelo é consideravelmente reduzida pelo comportamento super- hidrofóbico, devido à diminuição das forças de coesão (Kulinich, S.A; Farzanesh, M. Ice Adhesion on Super-hydrophobic Surfaces. Applied Surface Science, 8153-8157, 2009).  As commented by Kulinich and Farzaneh, there is a correlation between "gelophobic" behavior and superhydrophobic surfaces. Ice adhesion strength is considerably reduced by superhydrophobic behavior due to decreased cohesive forces (Kulinich, S.A; Farzanesh, M. Ice Adhesion on Superhydrophobic Surfaces. Applied Surface Science, 8153-8157, 2009).
Como disse Zhai e colaboradores, uma superfície super-hidrofóbica é a única que pode repelir completamente as gotas de água; tais superfícies apresentam ângulos de contato com a água (CA) igual ou superiores a 150°. (Zhai, L. et al. Stable Superhydrophobic Coating from Polyelectrolyte Multilayers. Nano Letters, 1349-1353, 2004). Por outro lado, Tourkine e colaboradores, salientaram que os revestimentos super-hidrofóbicos podem também atrasar o congelamento já que, por baixo da gota de água, de um modo geral, existe uma fina camada de ar aprisionado no interior das irregularidades da superfície, que podem proporcionar uma barreira térmica entre o sólido e o líquido (Tourkine, P. et al. Delayed Freezing on Water Repellent Materials. Langmuir, 7214-7216, 2009). A ideia de uma rugosidade controlada de superfície para criar um comportamento super-hidrofóbico associada a uma condição "gelofóbica" foi estudada por Wang e colaboradores. Eles aplicaram a decapagem para alterar a morfologia da superfície. Demonstraram que a força de adesão do gelo foi reduzida enquanto o ângulo de contato foi mantido maior do que 150°. No entanto, o processo de decapagem traz uma consequência, o aumento da rugosidade da superfície, que pode atrapalhar o fluxo de ar da camada limite levando a um aumento nas forças de arrasto. Por conseguinte, para as asas e as superfícies de controle da aeronave, a morfologia da superfície tem de ser alterada de tal forma que as forças aerodinâmicas não sejam perturbadas. Uma solução possível é a utilização de materiais nano-estruturados (Wang, F. et al. Ice Accretion on Superhydrophobic Aluminum Surfaces Under Low- Temperature Conditions. Cold Regions Science and Technoiogy, 29-33, 2010). As Zhai and colleagues have said, a superhydrophobic surface is the only one that can completely repel water droplets; Such surfaces have water contact angles (AC) of 150 ° or greater. (Zhai, L. et al. Stable Superhydrophobic Coating from Polyelectrolyte Multilayers. Nano Letters, 1349-1353, 2004). On the other hand, Tourkine and colleagues pointed out that superhydrophobic coatings can also delay freezing as there is generally a thin layer of air trapped beneath the surface of the surface of the surface of the water, which forms a trapped surface. may provide a thermal barrier between solid and liquid (Tourkine, P. et al. Delayed Freezing on Water Repellent Materials. Langmuir, 7214-7216, 2009). The idea of controlled surface roughness to create superhydrophobic behavior associated with a "gelophobic" condition has been studied by Wang and colleagues. They applied pickling to alter surface morphology. They demonstrated that the adhesion force of the ice was reduced while the contact angle was kept greater than 150 °. However, the pickling process has a consequence, increased surface roughness, which can disrupt the airflow of the boundary layer leading to an increase in drag forces. Therefore, for the wings and control surfaces of the aircraft, the surface morphology must be altered such that the aerodynamic forces are not disturbed. One possible solution is the use of nanostructured materials (Wang, F. et al. Ice Accretion on Superhydrophobic Aluminum Surfaces Under Low-Temperature Conditions. Cold Regions Science and Technoiogy, 29-33, 2010).
Lepore e colaboradores descreveram a criação de estruturas artificialmete super-hidrofóbicas pelo emprego de descarga elétrica (tratamento de coroa) para modificação de superfície de placas de poliestireno. Os resultados indicaram que o tratamento de coroa é uma técnica útil para "talhar" a tensão de superfícies de matrizes poliméricas (Lepore, E. et al. Plasma and Thermoforming Treatments to Tune the Bio-inspired Wettability of Polystyrene. Composites Part B, 2012, 43, 681 , 2012).  Lepore and colleagues described the creation of artificially superhydrophobic structures by the use of electrical discharge (corona treatment) for surface modification of polystyrene plates. The results indicated that crown treatment is a useful technique for "whitening" the surface tension of polymeric matrices (Lepore, E. et al. Plasma and Thermoforming Treatments to Tune the Bio-inspired Wettability of Polystyrene. Composites Part B, 2012 , 43, 681, 2012).
De acordo com Shang e colaboradores, materiais nano-estruturados podem também gerar superfícies hidrofóbicas. O trabalho de Shang envolveu uma enorme área de superfície contendo materiais nanoestruturados, que apresentou aumento da rugosidade e, consequentemente, da hidrofobicidade (Shang, H.M. et al. Nanostructured Superhydrophobic Surfaces. Journal of Materials Science, 3587-3591 , 2005.)  According to Shang and colleagues, nanostructured materials can also generate hydrophobic surfaces. Shang's work involved a huge surface area containing nanostructured materials that showed increased roughness and, consequently, hydrophobicity (Shang, H.M. et al. Nanostructured Superhydrophobic Surfaces. Journal of Materials Science, 3587-3591, 2005.)
Lau e colaboradores demonstraram o conceito de superfície super- hidrofóbica "engenhadas", baseadas em nanotubos de carbono. O trabalho de Lau foi sintetizar "florestas" de nanotubos de carbono (nanotubos de carbono alinhados verticalmente), revestidas com politetrafluoretileno (PTFE). Assim, abordaram duas questões importantes, ou seja, a grande área de superfície da "floresta" de nanotubos de carbono e a baixa energia de superfície de PTFE. De acordo com eles, a "floresta" de nanotubos de carbono sem revestimento de PTFE apresenta ângulo de contato da água em torno de 161 °; e um aumento de cerca de 5% no ângulo de contato foi obtido quando o revestimento de PTFE foi aplicado. Entretanto, o trabalho de Lau não estabeleceu uma relação entre a densidade dos nanotubos de carbono compactados e o fenómeno de hidrofobicidade (Lau, K.K.S. et al. "Superhydrophobic Carbon Nanotube Forest. Nano Letters, 1701 -1705, 2003)Lau and colleagues demonstrated the concept of "engineered" superhydrophobic surface based on carbon nanotubes. Lau's work was to synthesize "forests" of carbon nanotubes (vertically aligned carbon nanotubes) coated with polytetrafluoroethylene (PTFE). Thus, they addressed two important issues, namely the large surface area of the carbon nanotube "forest" and the low surface energy of PTFE. According to them, the "forest" of PTFE-coated carbon nanotubes has a water contact angle of around 161 °; and a 5% increase in contact angle was obtained when the PTFE coating was applied. However, Lau's work did not establish a relationship between the density of compacted carbon nanotubes and the hydrophobicity phenomenon (Lau, KKS et al. "Superhydrophobic Carbon Nanotube Forest. Nano Letters, 1701-1705, 2003)
Por outro lado, Li e colaboradores estudaram nanotubos de carbono densamente compactados alinhados verticalmente e filmes de nanotubos de carbono estruturados verticalmente alinhados formando estruturas como favo de mel. Os resultados mostraram um aumento moderado no ângulo de contato (de 158,5° para 163,4°) quando os nanotubos de carbono foram estruturados como um favo de mel quando comparados com os nanotubos de carbono densamente compactados. Apesar do fato de ambos os grupos (Lau e Li) de pesquisa terem obtido superfícies super-hidrofóbicas, existem algumas limitações que devem ser abordadas. A primeira é a tendência de nanotubos de carbono em agrupar-se sob forças de tensão superficial durante a secagem, e a segunda limitação é o aspecto da proporção (relação) diâmetro/comprimento. Em "florestas" de nanotubos de carbono com proporções pequenas (relações entre diâmetro/comprimento), a água é fortemente atraída para a superfície de base devido à histerese (Li, S. et al. Super-Hydrophobicity of Large-Area Honeycomb-like Aligned Carbon Nanotubes. Journal of Physical Chemestry B, 9274-9276, 2002). In contrast, Li and colleagues studied vertically aligned densely packed carbon nanotubes and vertically aligned structured carbon nanotube films forming honeycomb structures. The results showed a moderate increase in contact angle (from 158.5 ° to 163.4 °) when carbon nanotubes were structured like a honeycomb when compared to densely packed carbon nanotubes. Despite the fact that both research groups (Lau and Li) have obtained superhydrophobic surfaces, there are some limitations that should be addressed. The first is the tendency of carbon nanotubes to cluster under surface tension forces during drying, and the second limitation is the aspect ratio (diameter) to length ratio. In "forests" of small carbon nanotubes (diameter / length ratios), water is strongly attracted to the base surface due to hysteresis (Li, S. et al. Super-Hydrophobicity of Large-Area Honeycomb-like Aligned Carbon Nanotubes, Journal of Physical Chemistry B, 9274-9276, 2002).
Lafuma e Quéré desenvolveram artificialmente superfícies hidrofóbicas e super-hidrofóbicas, através da modificação por microtexturização. Embora eles fossem capazes de medir um ângulo de contato de 164°, foi evidenciado que microtexturas podem ser preenchidas com água, especialmente quando a condensação está presente, o que atrapalha na impermeabilização da água à membrana em questão (Lafuma, A; Quéré, D. Superhydrophobic States. Nature Materials, 2(7):457-460, 2003).  Lafuma and Quéré artificially developed hydrophobic and superhydrophobic surfaces through modification by microtexturization. Although they were able to measure a contact angle of 164 °, it was found that microtextures can be filled with water, especially when condensation is present, which hinders the waterproofing of the membrane in question (Lafuma, A; Quéré, D Superhydrophobic States, Nature Materials, 2 (7): 457-460, 2003).
Jin e colaboradores, criaram uma nanoestrutura do "tipo Gecko" baseada em um modelo poroso de nanoescala que permite a formação de uma área fortemente densa de nanotubos de poliestireno. Essa nanoestrutura apresentou uma superfície super-hidrofóbica, com ângulo de contato da água (CA) em torno de 162°. A principal desvantagem do trabalho de Jin é a complexidade da fabricação (Jin, M. et al. Superhydrophobic Aligned Polystyrene Nanotube Film with High Adhesive Force. Advanced Materials, 17(6):1977-1981 , 2005). Jin and colleagues created a "Gecko-like" nanostructure based on a porous nanoscale model that allows the formation of a strongly dense area of polystyrene nanotubes. This nanostructure had a superhydrophobic surface with water contact angle (CA) around 162 °. The main disadvantage of Jin's work is the complexity of manufacturing (Jin, M. et al. Superhydrophobic Aligned Polystyrene Nanotube Film with High Adhesive Force. Advanced Materials, 17 (6): 1977-1981, 2005).
Um processo mais simples e fácil foi proposto por Jiang e colaboradores. A rugosidade de superfície necessária para obter uma superfície hidrofóbica pode ser adquirida através da deposição de nanofibras orientadas aleatoriamente, e a energia superficial baixa pode ser conseguida utilizando poliestireno (PS). A técnica de eletrofiação foi empregada para a obtenção da nanomembrana. O ângulo de contato da água (CA) apresentado, variou de 139° a 162° em função da proporção da matriz/solvente. O melhor resultado relatado foi uma mistura de nanofibras e microesferas, mas devido à dispersão das microesferas, a homogeneidade da superfície não pode ser garantida (Jiang, L. et al. A Lotus-Leaf-like Superhydrophobic Surface: A Porous Microsphere/Nanofiber Composite Film Prepared by Electrohydrodynamics. Angew. Chem, 1 16(15), 4438-4441 , 2004).  A simpler and easier process has been proposed by Jiang and colleagues. The surface roughness required to obtain a hydrophobic surface can be achieved by randomly oriented nanofiber deposition, and low surface energy can be achieved using polystyrene (PS). The electrophony technique was used to obtain the nanomembrane. The water contact angle (AC) presented ranged from 139 ° to 162 ° as a function of matrix / solvent ratio. The best reported result was a mixture of nanofibers and microspheres, but due to the dispersion of microspheres, surface homogeneity cannot be guaranteed (Jiang, L. et al. A Lotus-Leaf-like Superhydrophobic Surface: A Porous Microsphere / Nanofiber Composite Film Prepared by Electrohydrodynamics (Angew Chem, 16 (15), 4438-4441, 2004).
Kang e colaboradores usou também eletrofiação e poliestireno, mas com diferentes parâmetros operacionais. Considerando uma proporção matriz/solvente muito maior, este valor atingiu 35% enquanto no artigo de Jiang esse valor foi limitado a 25%. Kang obteve um conjunto mais uniforme de nanofibras. O CA da água, no entanto, atingiu o valor máximo de 154°. Esta limitação se deve aos diâmetros e morfologia das nanofibras que podem ser influenciadas por diferentes solventes utilizados, como por exemplo, clorofórmio (CHCI3), Ν,Ν'-dimetilformamida (DMF) e tetrahidrofurano (THF) e suas razões de fluxo (KANG, M. et al. Preparation of Superhydrophobic Polystyrene Membranes by Electrospinning. Colloids and Suríaces A. Physicochemistry Engineering Aspects, 313-314(2), 41 1 -41 , 2008). Kang et al. Also used electroporation and polystyrene, but with different operating parameters. Considering a much higher matrix / solvent ratio, this figure reached 35% while in Jiang's article this value was limited to 25%. Kang obtained a more uniform set of nanofibers. The water AC, however, reached the maximum value of 154 °. This limitation is due to nanofiber diameters and morphology that may be influenced by different solvents used, such as chloroform (CHCl 3 ), Ν, Ν'-dimethylformamide (DMF) and tetrahydrofuran (THF) and their flow ratios (KANG). , M. et al., Preparation of Superhydrophobic Polystyrene Membranes by Electrospinning, Colloids and Surfaces A. Physicochemistry Engineering Aspects, 313-314 (2), 41 1-41, 2008).
Miyauchi e colaboradores descreveram o processo de obtenção de uma membrana auto-limpante de caráter super-hidrofóbico à base de uma solução de poliestireno 30% pt em taxas diversas de DM F/TH F - 4/0 , 3/1 , 2/2, 1/3 e 0/4, respectivamente. Após a solubilização do polímero, a mistura foi exposta à técnica de eletrofiação. O material obtido apresentou CA superiores a 159,5°, o que caracteriza a super-hidrofobicidade da membrana. Entretanto, as nanofibras obtidas pelo uso de DM F/PS não foram completamente homogéneas, havendo formação de microesferas de PS o que limita o seu caráter de super-hidrofobicidade. Vale a pena ressaltar também que o valor máximo de CA (159,5°) foi obtido somente para a mistura de THF/DMF à taxa de 1/3 para 30% em peso de PS (Miyauchi, Y. et al. Fabrication of a silver- ragwort-leaf-like super-hydrophobic micro/nanoporous fibrous mat surface by electrospinning. Nanotechnology, 17, 5151-5156, 2006). Miyauchi and colleagues described the process of obtaining a super-hydrophobic self-cleaning membrane based on a 30% polystyrene solution at varying DM F / TH rates F - 4/0, 3/1, 2/2 , 1/3 and 0/4, respectively. After solubilization of the polymer, the mixture was exposed to the electrophony technique. The obtained material presented AC higher than 159.5 °, which characterizes the superhydrophobicity of the membrane. However, the nanofibers obtained by the use of DM F / PS were not completely homogeneous, with formation of PS microspheres which limits their superhydrophobicity character. It is also worth noting that the maximum value of CA (159.5 °) was obtained only for the THF / DMF mixture at the rate of 1/3 to 30 wt% PS (Miyauchi, Y. et al. Fabrication of a silver-ragwort-leaf-like superhydrophobic micro / nanoporous fibrous mat surface by electrospinning (Nanotechnology, 17, 5151-5156, 2006).
O pedido de patente US2002150723 intitulado "Suríaces which are self- cleanig by hydrophobic structures, and a process for their production" descreve o processo de obtenção de estruturas hidrofóbicas micrométricas a partir da utilização de polímeros, dentre esses, o poliestireno, para a produção de superfícies com características "auto-limpantes". Na tecnologia foram introduzidas, ao polímero, partículas de sílica, óxido de alumínio e silicatos, previamente tratados com substâncias hidrofóbicas, como, por exemplo, cera, óleo, dentre outros. O material obtido não se mostrou super-hidrofóbico e não apresentou propriedades anti-congelantes.  US2002150723 entitled "Suraces which are self-cleaning by hydrophobic structures, and a process for their production" describes the process of obtaining micrometric hydrophobic structures from the use of polymers, including polystyrene, for the production of surfaces with "self-cleaning" characteristics. In the technology were introduced to the polymer, silica particles, aluminum oxide and silicates, previously treated with hydrophobic substances, such as wax, oil, among others. The material obtained was not superhydrophobic and did not have antifreeze properties.
O pedido de patente KR201 10059173 intitulado "Superhydrophobic coating composition, superhydrophobic coating film using the same, and method of manufacturing thereof" descreve o processo de obtenção de composições de revestimento super-hidrofóbico através da deposição de óxido de grafeno à estrutura de um polímero hidrofóbico contendo flúor, podendo ser utilizadas como revestimento auto-limpante e anti-incrustante. Essa tecnologia, contudo, utiliza a porcentagem em peso de grafeno de 3,0% a 30%, o que difere do presente pedido, que é de 0,5%. Além disso, o filme super-hidrofóbico obtido do supracitado pedido de patente não possui propriedades anticongelantes .  Patent Application KR201 10059173 entitled "Superhydrophobic coating composition, using the same, and method of manufacturing thereof" describes the process of obtaining superhydrophobic coating compositions by depositing graphene oxide on the structure of a hydrophobic polymer. containing fluoride and can be used as a self-cleaning and antifouling coating. This technology, however, uses the graphene weight percentage from 3.0% to 30%, which differs from the present application, which is 0.5%. In addition, the superhydrophobic film obtained from the above patent application has no antifreeze properties.
O pedido de patente EP2484431 descreve o processo de obtenção de nanomembranas hidrofóbicas através da utilização de uma mistura de pelo menos dois tipos de polímeros lipofílicos selecionados do grupo dos seguintes polímeros: poliestireno, polietileno, poliuretano, nylon, poliacrinonitrila, polimetilmetacrilato, policloreto de vinila, dissolvidos em solventes orgânicos e expostos à técnica de eletrofiação para obtenção de fibras nanométricas de caráter hidrofobico. Entretanto, a citada tecnologia exige um tratamento por plasma para conferir a hidrofobicidade na nanomembrana e, mesmo assim.a nanomembrana obtida não é super-hidrofóbica. EP2484431 describes the process of obtaining hydrophobic nanomembranes by using a mixture of at least two types of lipophilic polymers selected from the group of the following: Polymers: polystyrene, polyethylene, polyurethane, nylon, polyacrylonitrile, polymethyl methacrylate, polyvinyl chloride, dissolved in organic solvents and exposed to electrophilization technique to obtain hydrophobic nanometric fibers. However, said technology requires a plasma treatment to check the hydrophobicity in the nanomembrane and yet the nanomembrane obtained is not superhydrophobic.
Os pedidos de patentes US2007166464, KR20060041314 e KR20120018521 descrevem o processo de obtenção de nanofibras super- hidrofóbicas a partir de um polímero hidrofobico, podendo este ser o poliestireno, previamente dissolvido em solvente orgânico e exposto à técnica de eletrofiação para a obtenção das fibras nanométricas super-hidrofóbicas. Entretanto, o caráter super-hidrofóbico da respectiva nanofibra é atribuído a adição de um fluoropolímero ou um siloxano à solução PS/solvente. Além disso, não são relatados nos pedidos supracitados o uso da nanomembrana para um sistema de anti-congelamento.  US2007166464, KR20060041314 and KR20120018521 describe the process of obtaining superhydrophobic nanofibers from a hydrophobic polymer, which may be polystyrene previously dissolved in an organic solvent and exposed to the electrophony technique for obtaining super nanometric fibers. -hydrophobic. However, the superhydrophobic character of the respective nanofiber is attributed to the addition of a fluoropolymer or siloxane to the PS / solvent solution. In addition, the above applications do not report the use of nanomembrane for an anti-freeze system.
Os pedidos de patentes US20110168980, KR20 00105179 e KR20100105179 descrevem o processo de obtenção de um compósito de nanofibras e de películas transparentes formadas por um polímero hidrofobico através da técnica de eletrofiação, podendo esse polímero ser o poliestireno, sendo que é adicionado a esse polímero um material orgânico semicondutor, podendo esse material ser nanotubo de carbono ou grafeno. Contudo, a adição de grafeno ou de nanotubos de carbono têm o objetivo de prover propriedades elétricas e ópticas ao material referido, ou seja, não são súper-hidrofóbicos nem apresentam a finalidade anti-congelante..  US20110168980, KR20 00105179 and KR20100105179 describe the process of obtaining a composite of nanofibers and transparent films formed by a hydrophobic polymer by the electrophony technique, which polymer may be polystyrene, and a polymer is added thereto. semiconductor organic material, which material may be carbon nanotube or graphene. However, the addition of graphene or carbon nanotubes is intended to provide electrical and optical properties to the material referred to, ie, they are not superhydrophobic or anti-freeze.
O pedido de patente KR746643 intitulado "Method for producing superhydrophobic fibrous membrane by electrospinning a solution prepared by dissolving polystyrene into a non-volatile solvent, and superhydrophobic fibrous membrane produced by the method" descreve o processo de obtenção de uma membrana polimérica super-hidrofóbica a partir de um polímero hidrofobico, o poliestireno, dissolvido em solvente orgânico DMF para ser eletrofiado. O documento supracitado relata a utilização apenas do poliestireno para a obtenção da membrana super-hidrofóbica, e o ângulo de contato com a água (CA) obtido é em tomo de 150°. A faixa de concentração de PS utilizado situou- se entre 30 a 40% em partes por peso e a membrana obtida não tem utilização como um sistema eficiente de anti-congelamento. Patent Application KR746643 entitled "Method for producing superhydrophobic fibrous membrane by electrospinning a solution prepared by dissolving polystyrene into a non-volatile solvent, and superhydrophobic fibrous membrane produced by the method" describes the process of obtaining a superhydrophobic polymeric membrane to From a hydrophobic polymer, polystyrene, dissolved in DMF organic solvent to be electrophilized. The above document reports the use of polystyrene only to obtain the superhydrophobic membrane, and the contact angle with water. (CA) obtained is about 150 °. The concentration range of PS used was between 30 and 40% in parts by weight and the obtained membrane has no use as an efficient antifreeze system.
O pedido de patente PI0903844 intitulado "Método e aparelho para produzir mantas de micro e/ou nanofibras a partir de polímeros, seus usos e métodos de revestimento" descreve um processo para obtenção de nano e micro fibras a partir de um grupo de polímeros entre esses, o poliestireno, previamente dissolvido em um solvente orgânico, que podem ser carregados com partículas orgânicas como nanofibras de carbono ou inorgânicas, como exemplo, o ZnO. Para a obtenção das fibras nanométricas são usados jatos de ar em alta velocidade. Entretanto, o uso desta membrana hidrofóbica limita-se principalmente à impermeabilização: utensílios de limpeza, em roupas impermeáveis e protetoras contra agentes químicos, biológicos, não sendo utilizável como uma barreira para congelamento.  Patent application PI0903844 entitled "Method and apparatus for producing micro and / or nanofiber blankets from polymers, their uses and coating methods" describes a process for obtaining nano and micro fibers from a group of polymers between them. polystyrene, previously dissolved in an organic solvent, which may be charged with organic particles such as carbon nanofibers or inorganic, for example, ZnO. To obtain the nanometric fibers, high speed air jets are used. However, the use of this hydrophobic membrane is mainly limited to waterproofing: cleaning utensils, in impervious clothing and protective against biological and chemical agents, not being usable as a barrier for freezing.
Apesar da utilização da técnica de eletrofiação de uma solução poliestireno/solvente para obtenção de estruturas de dimensões nanométricas, hidrofóbicas e super-hidrofóbicas ser bem conhecido na literatura, o processo de produção de nanomembranas proposto no presente pedido gera nanomembranas de poliestireno super-hidrofóbicas com valores de CA superiores a 150° que provém excelente resistência à adesão ou interação da água com a superfície recoberta pela nanomembrana. Além do uso como impermeabilizantes e anti-incrustantes, as nanomembranas super-hidrofóbicas obtidas também possuem propriedades anti-congelantes, dentre outros.  Although the use of the electrophony technique of a polystyrene / solvent solution to obtain nanometric, hydrophobic and superhydrophobic structures is well known in the literature, the nanomembrane production process proposed in the present application generates superhydrophobic polystyrene nanomembranes with AC values above 150 ° provide excellent resistance to adhesion or interaction of water with the surface covered by the nanomembrane. In addition to being used as waterproofing and antifouling, the superhydrophobic nanomembranes obtained also have antifreeze properties, among others.
DESCRIÇÃO DAS FIGURAS A Figura 01 mostra um gráfico das medições da viscosidade dinâmica da solução PS/DMF, com ou sem inserção de nanopartículas, durante a técnica de eletrofiação. DESCRIPTION OF THE DRAWINGS Figure 01 shows a graph of the dynamic viscosity measurements of the PS / DMF solution, with or without nanoparticle insertion, during the electrophony technique.
A Figura 02 mostra os valores dos ângulos de contacto com a água (CA) para todos os nove grupos de experimentos. A Figura 03 mostra a imagem em microscopia eletrônica de varreduraFigure 02 shows the water contact angle (AC) values for all nine experiment groups. Figure 03 shows the scanning electron microscopy image
(SEM) da nanomembrana de PS/DMF. A Figura 04 mostra uma gota de água sobre a nanomembrana de PS/DMF. (SEM) of the PS / DMF nanomembrane. Figure 04 shows a drop of water on the PS / DMF nanomembrane.
A Figura 05 mostra uma imagem em microscopia (SEM) em alta ampliação da superfície da nanomembrana de PS/DMF ressaltando as suas rugosidades. Figure 05 shows a high magnification microscopy (SEM) image of the surface of the PS / DMF nanomembrane highlighting its roughness.
A Figura 06 mostra a imagem de uma gota de água sobre as nanofibras PS/DM F/grafeno. Figure 06 shows the image of a drop of water on PS / DM F / graphene nanofibers.
A Figura 07 mostra uma imagem em microscopia (SEM) da nanomembrana de PS/DMF/grafeno. A Figura 08 mostra uma imagem em microscopia (SEM) em alta ampliação das rugosidades da nanofibra de PS/DMF/grafeno. Figure 07 shows a microscopic (SEM) image of the PS / DMF / graphene nanomembrane. Figure 08 shows a high magnification microscopy (SEM) image of the PS / DMF / graphene nanofiber roughness.
A Figura 09 mostra uma imagem em microscopia (SEM) de uma gota de água "sentada" em feixes de nanosílica sobre a nanomembrana de PS/DMF/nanosílica. A Figura 10 mostra as nanofibras obtidas pela dispersão de nanosílica à solução PS/DMF. Figure 09 shows a microscopic (SEM) image of a water droplet "sitting" in nanosilic bundles on the PS / DMF / nanosilic nanomembrane. Figure 10 shows the nanofibers obtained by dispersing nanosilicide to the PS / DMF solution.
A Figura 11 mostra uma imagem em microscopia (SEM) em alta ampliação da superfície rugosa de PS/DMF/nanosílica com partículas de nanosílica incrustadas. A Figura 12 apresenta a imagem de uma gota de água sobre a superfície da nanomembrana de PS/DMF/CdS. Figure 11 shows a high magnification microscopy (SEM) image of the rough surface of PS / DMF / nanosilum with encrusted nanosilic particles. Figure 12 shows the image of a drop of water on the surface of the PS / DMF / CdS nanomembrane.
A Figura 13 mostra uma imagem em microscopia (SEM) das nanofibras de PS/DMF/CdS com alguns agrupamentos de sulfeto de cádmio (partículas brancas brilhantes) que podem ser vistos entre as fibras.A Figura 14 mostra a rugosidade de uma nanofibra de PS/DM F/CdS em que a nanofibra de poliestireno recobre parcialmente o CdS. Figure 13 shows a microscopic (SEM) image of PS / DMF / CdS nanofibers with some cadmium sulfide clusters (bright white particles) that can be seen between the fibers. Figure 14 shows the roughness of a PS nanofiber. / DM F / CdS where polystyrene nanofiber partially covers the CdS.
A Figura 15 mostra a imagem em microscopia (SEM) da nanomembrana de PS/DMF/ZnS com 5,0% m/m. A Figura 16 mostra uma imagem em microscopia (SEM) da nanomembrana de PS/DMF/ZnS com 10,0% m/m. Figure 15 shows the microscopic (SEM) image of the 5.0% w / w PS / DMF / ZnS nanomembrane. Figure 16 shows a microscopic (SEM) image of the 10.0% w / w PS / DMF / ZnS nanomembrane.
A Figura 17 mostra uma imagem em microscopia (SEM) da nanomembrana de PS/DMF/ZnS com 15,0% m/m. A Figura 18 mostra uma gota de água sobre a superfície da nanomembrana obtida a partir do Grupo 09. Figure 17 shows a microscopic (SEM) image of the 15.0% w / w PS / DMF / ZnS nanomembrane. Figure 18 shows a drop of water on the nanomembrane surface obtained from Group 09.
A Figura 19 mostra os valores para a energia superficial, considerando o modelo de Neumann para cada conjunto de membranas testadas. Figure 19 shows the values for surface energy, considering the Neumann model for each set of membranes tested.
A Figura 20 mostra uma gota de água em forma líquida a -7 °C situado sobre as nanomembranas. Figure 20 shows a drop of liquid water at -7 ° C situated on the nanomembranes.
DESCRIÇÃO DETALHADA DA TECNOLOGIA DETAILED DESCRIPTION OF TECHNOLOGY
As nanomembranas super-hidrofóbicas, objetos da presente invenção, são obtidas pela técnica de eletrofiação. Esta técnica permite a preparação de fibras de diâmetros nanométricos, variando entre 1 ,37 a 4,13 μιτι através da aplicação de um campo elétrico entre a solução polímero/solvente e o substrato alvo. As soluções polímero/solvente possuem concentrações que podem variar entre 20 a 35% m/m de polímero e, são preparadas pela adição do polímero ao solvente sob agitação constante de 200 rpm e aquecimento a 40°C.  The superhydrophobic nanomembranes, objects of the present invention, are obtained by the electrophony technique. This technique allows the preparation of fibers of nanometric diameters, ranging from 1.37 to 4.13 μιτι by applying an electric field between the polymer / solvent solution and the target substrate. Polymer / solvent solutions have concentrations ranging from 20 to 35% w / w polymer and are prepared by adding the polymer to the solvent under constant stirring at 200 rpm and heating at 40 ° C.
Quando o polímero é totalmente solubilizado, a solução, então, é resfriada até atingir a temperatura ambiente (entre 20 e 25°C). Em seguida, as nanopartículas são adicionadas, separadamente, à solução e esta é sonificada. When the polymer is fully solubilized, the solution is then cooled to room temperature (between 20 and 25 ° C). Then the nanoparticles are added separately to the solution and the solution is sonicated.
A técnica de eletrofiação utilizada na obtenção das nanomembranas é um processo consideravelmente eficiente, rápido e não oneroso na fabricação de materiais de dimensões nanométricas e ou micrométricas. O equipamento de eletrofiação utilizado para a obtenção das nanomembranas é composto basicamente por uma fonte de alta tensão, uma bomba de infusão, um tubo capilar de aço inoxidável e um cilindro rotativo. A solução polímero/solvente/nanopartícula é inserida no aparelho de eletrofiação através de uma pequena entrada (orifício metálico) e submetida a uma diferença de potencial elétrico em relação a um alvo coletor, também metálico. O solvente é separado do polímero à medida que a mistura é ejetada formando, assim, fibras nanométricas, que se depositam no anteparo/substrato. The electrophony technique used to obtain nanomembranes is a considerably efficient, fast and inexpensive process in the manufacture of nanometer and / or micrometer sized materials. The electrophony equipment used to obtain the nanomembranes is basically composed of a high voltage source, an infusion pump, a stainless steel capillary tube and a rotary cylinder. The polymer / solvent / nanoparticle solution is inserted into the electrophony apparatus through a small inlet (metal hole) and subjected to an electrical potential difference from a collecting target, also metallic. The solvent is separated from the polymer as the mixture is ejected, thus forming nanometric fibers that deposit on the bulkhead / substrate.
O processo é controlado pelo campo elétrico estabelecido (mantido constante nesse caso) pela bomba de infusão e pela viscosidade do fluido. O alvo coletor representa o anteparo metálico onde a malha composta por fibras formadas é coletada durante o processo. Após o término do processo, esta membrana é colocada sobre uma superfície de alumínio.  The process is controlled by the electric field established (kept constant in this case) by the infusion pump and the fluid viscosity. The collecting target represents the metallic bulkhead where the mesh composed of formed fibers is collected during the process. Upon completion of the process, this membrane is placed on an aluminum surface.
Os solventes que podem ser utilizados no processo são selecionados do grupo compreendendo tetracloreto de carbono, clorofórmio, dimetilsulfóxido (DMSO), hexano, tolueno, benzeno, preferencialmente, dimetilformamida (DMF) ou o tetrahidrofurano (THF).  The solvents that may be used in the process are selected from the group comprising carbon tetrachloride, chloroform, dimethyl sulfoxide (DMSO), hexane, toluene, benzene, preferably dimethylformamide (DMF) or tetrahydrofuran (THF).
Dentre os polímeros hidrofóbicos de significativa importância, para obtenção de membranas super-hidrofóbicas, podem ser citados o poliuretano (PU), o polióxido de etileno (PEO), o politeraftalato de etileno (PET), o polifluoreto de vinilideno (PVDF) e o poliestireno (PS) devido à baixa tensão superficial desse polímero, o que o caracteriza naturalmente como hidrofóbico.  Among the hydrophobic polymers of significant importance, to obtain superhydrophobic membranes, polyurethane (PU), ethylene polyoxide (PEO), polyethylene terephthalate (PET), vinylidene polyfluoride (PVDF) and polystyrene (PS) due to the low surface tension of this polymer, which characterizes it naturally as hydrophobic.
Os materiais super-hidrofóbicas obtidos na presente invenção, na forma de membranas ou de películas são constituídos por nanofibras tramadas como um tipo de "pele" através da técnica de eletrofiação, a partir de um polímero, preferencialmente o PS. As espessuras das nanomembranas podem variar, , dependendo do tipo das nanopartículas utilizadas, que podem ser metálicas ou não metálicas.  The superhydrophobic materials obtained in the present invention in the form of membranes or films are nanofibers woven as a type of "skin" by the technique of electrophony from a polymer, preferably PS. Nanomembrane thicknesses may vary depending on the type of nanoparticles used, which may be metallic or non-metallic.
As nanopartículas utilizadas como agentes dopantes na obtenção das nanomembranas super-hidrofóbicas adicionadas à solução de polímero/solvente compreendem grafeno, nanosílica, sulfeto de cádmio (CdS) e sulfeto de zinco (ZnS). Vale salientar que o grafeno foi obtido segundo processo descrito por Ávila e colaboradores (Ávila, A.F. et al. Composites. Part B, 41 (2), 380-387, 2010). As concentrações das soluções empregadas com nanopartículas variaram entre 0,1 a 20,0% preferencialmente 0,5% m/m de grafeno, 0,5 a 1 ,0% m/m de nanosílica, 5,0% de CdS, e 10 a 15% m/m de ZnS.  Nanoparticles used as doping agents to obtain superhydrophobic nanomembranes added to the polymer / solvent solution comprise graphene, nanosilium, cadmium sulfide (CdS) and zinc sulfide (ZnS). It is noteworthy that graphene was obtained according to the process described by Ávila and colleagues (Ávila, A.F. et al. Composites. Part B, 41 (2), 380-387, 2010). The concentrations of the nanoparticle solutions employed ranged from 0.1 to 20.0%, preferably 0.5% w / w graphene, 0.5 to 1.0% w / w nanosilica, 5.0% CdS, and 10 to 15% w / w ZnS.
Todas as nanopartículas foram adicionadas separadamente à solução de PS/solvente e eletrofiadas, conforme mencionado anteriormente. Após a formação da nanomembrana, a mesma foi depositada diretamente sob um substrato de alumínio. Testes de hidrofobicidade foram realizados, e como resultado, os ângulos de contatos com a água (CA) variaram entre 150 e 168°. A Figura 18 mostra uma gota de água sobre a superfície da nanomembrana obtida a partir pela inserção de 15,0% m/m de ZnS, sendo que o valor do ângulo de contato superior a 167°. All nanoparticles were added separately to the PS / solvent solution and electroplated as mentioned above. After nanomembrane formation, it was deposited directly under an aluminum substrate. Hydrophobicity tests were performed, and as a result, water contact angles (AC) ranged from 150 to 168 °. Figure 18 shows a drop of water on the nanomembrane surface obtained from the insertion of 15.0% w / w ZnS, with the contact angle value exceeding 167 °.
Visto que a rugosidade é uma característica importante na busca de se obter uma superfície hidrofóbica, a inserção das nanopartículas à solução de polímero/solvente eletrofiados proporcionou a formação de rugosidades nanométricas nas fibras de poliestireno obtidas. Isso pode ser visualizado na Figura 8, cuja imagem em microscopia eletrônica de varredura de alta ampliação da nanofibra de poliestireno dopada com grafeno revelou uma superfície descontínua e rugosa com cavidades nanométricas de 120 ± 5 nm em comprimento por 7 ± 0,8 nm de largura. Nas Figuras 15 e 16 pode-se perceber que a adição de ZnS 10% e 15 % m/m, respectivamente, gerou um acúmulo de nanopartículas de ZnS, o que ocasionou o aumentou da rugosidade da nanofibra e, consequentemente, o aumento do ângulo de contato com a água. Para essas concentrações de ZnS, os valores de CA aferidos foram: (163,49 ± 4,93)° e (168,22 ± 3,19)° para adição de 10% e 15% m/m de ZnS respectivamente.  Since roughness is an important feature in the pursuit of a hydrophobic surface, the insertion of nanoparticles into the electroplated polymer solution / solvent provided the formation of nanometric roughness in the obtained polystyrene fibers. This can be seen in Figure 8, whose high-magnification scanning electron microscopy image of graphene-doped polystyrene nanofiber revealed a rough, discontinuous surface with nanometric cavities of 120 ± 5 nm in length by 7 ± 0.8 nm in width. . In Figures 15 and 16 it can be seen that the addition of 10% and 15% w / w ZnS, respectively, generated an accumulation of ZnS nanoparticles, which increased the nanofiber roughness and, consequently, increased the angle. contact with water. For these ZnS concentrations, the measured AC values were: (163.49 ± 4.93) ° and (168.22 ± 3.19) ° for the addition of 10% and 15% w / w ZnS respectively.
Como já mencionado, as nanomembranas super-hidrofóbicas têm interação muito baixa com a água, e isto evita que a água ou umidade se deposite e congele em determinadas superfícies. Por esse motivo, as nanomembranas super-hidrofóbicas podem ser aplicadas como sistemas anti- congelamento em equipamentos de refrigeração, superfícies de aeronaves e fios de alta tensão, e também na impermeabilização de superfícies. Assim, a Figura 20 mostra uma gota de água em forma líquida a -7 °C situada sobre as nanomembranas dopadas com 15% m/m de ZnS. Devido à super- hidrofobicidade da membrana obtida, a interação da gota de água com a superfície se torna insignificante evitando, portanto, que a água se congele e fique incrustada sobre a superfície. Esta invenção pode ser mais bem compreendida através dos seguintes exemplos, não limitantes. As already mentioned, superhydrophobic nanomembranes have very low interaction with water, and this prevents water or moisture from settling and freezing on certain surfaces. For this reason, superhydrophobic nanomembranes can be applied as anti-freeze systems in refrigeration equipment, aircraft surfaces and high voltage wires, as well as in waterproofing surfaces. Thus, Figure 20 shows a drop of water in liquid form at -7 ° C situated on the doped nanomembranes containing 15% w / w ZnS. Due to the superhydrophobicity of the membrane obtained, the interaction of the water droplet with the surface becomes insignificant, thus preventing water from freezing and becoming embedded in the surface. This invention may be better understood by the following non-limiting examples.
EXEMPLO 1 - Processo geral de preparação das nanomembranas  EXAMPLE 1 - General Process of Nanomembrane Preparation
Em uma primeira etapa, o PS (190,000 g/mol) foi adicionado a um solvente orgânico (DMF), sob leve agitação (200 rpm) à temperatura de 40°C, por um período de tempo variando entre 30 a 60 minutos. Optou-se por utilizar uma concentração entre 35% de percentagem em massa como limite superior e 20% de percentagem em massa como limite inferior.  In a first step, PS (190,000 g / mol) was added to an organic solvent (DMF) under gentle stirring (200 rpm) at 40 ° C for a period of time ranging from 30 to 60 minutes. A concentration between 35% by weight as the upper limit and 20% by weight as the lower limit was chosen.
Após a solução PS/DM F atingir a temperatura ambiente (20 a 25 °C) adiciona-se a nanopartícula (sulfeto de zinco, sulfeto de cádmio, grafeno ou nanosílica). Para a solubilização completa foi usado um sonicador, a uma frequência de 20 KHz durante um período variando entre 30 e 60 minutos.  After the PS / DM F solution reaches room temperature (20 to 25 ° C) the nanoparticle (zinc sulfide, cadmium sulfide, graphene or nanosilic) is added. For complete solubilization a sonicator was used at a frequency of 20 KHz for a period ranging from 30 to 60 minutes.
Já a adição dos núcleos metálicos de zinco e de cádmio proporcionaram uma maior rugosidade à estrutura do poliestireno, o que propiciou à estrutura da nanomembrana um carácter hidrofóbico mais intenso (Carré e Adhes, 2007).  The addition of zinc and cadmium metal cores provided greater roughness to the polystyrene structure, which gave the nanomembrane structure a more intense hydrophobic character (Carré and Adhes, 2007).
Após a dissolução das nanopartículas na solução de PS/DMF, foi utilizada a técnica de eletrofiação descrita segundo Andrady e KO (Andrady, A. After dissolution of the nanoparticles in the PS / DMF solution, the electroporation technique described according to Andrady and KO (Andrady, A.) was used.
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Electrospinning for Tissue Engineering. in Nanofibers and Nanotechnology inElectrospinning for Tissue Engineering. in Nanofibers and Nanotechnology in
Textiles. Woodhead Publishing, 22-44, 2008). Textiles Woodhead Publishing, 22-44, 2008).
O aparelho de eletrofiação utilizado é composto por um fornecedor de alta tensão, uma bomba de infusão, um tubo capilar de aço inoxidável e um cilindro rotativo. A taxa de fluxo utilizada foi estabelecida entre 17 a 33 pL/min a uma tensão aplicada de 15 KV. A densidade do campo elétrico aplicado foi de The electrophony apparatus used consists of a high voltage supplier, an infusion pump, a stainless steel capillary tube and a rotary cylinder. The flow rate used was set at 17 to 33 pL / min at an applied voltage of 15 KV. The density of the applied electric field was
150 KV/m e foi mantido constante nos experimentos. A distância entre a extremidade da agulha e a placa foi cerca de 10 cm. 150 KV / m and was kept constant in the experiments. The distance between the needle tip and the plate was about 10 cm.
Para medir o ângulo de contato com a água foi utilizado uma micropipeta (0,1 -1 ,0) μΐ_ e água destilada. Um microscópio metalográfico com uma câmera digital (3,0 MP) coletou as imagens. A morfologia de nanofibras foi investigada por microscópio eletronico de varredura. As imagens foram processadas por software. Foram avaliadas as alterações da morfologia da nanomembrana após dopagem com as diferentes nanopartículas já referenciadas através da medição da viscosidade. To measure the contact angle with water was used a micropipette (0.1 -1, 0) μΐ_ and distilled water. A metallographic microscope with a digital camera (3.0 MP) collected the images. Nanofiber morphology was investigated by scanning electron microscope. The images were processed by software. Changes in nanomembrane morphology after doping with different nanoparticles already referenced were evaluated by measuring viscosity.
EXEMPLO 2 - Escolha dos diferentes grupos de testes EXAMPLE 2 - Choice of Different Test Groups
Para avaliar os valores obtidos dos CA's das nanomembranas de poliestireno, optou-se por separar as membranas em grupos de 01 a 09 onde todos contêm a matriz de poliestireno e diferentes materiais de dopagem em diferentes concentrações (zinco, cádmio, grafeno esfoliado ou nanosílica). As taxas de solução PS/DMF utilizadas foram de 33 pL/min para as nanomembranas sem adição de nanopartículas e 17 pL/min para nanomembranas dopadas com nanopartículas.  In order to evaluate the CA values obtained from polystyrene nanomembranes, we chose to separate the membranes into groups from 01 to 09 where they all contain the polystyrene matrix and different doping materials in different concentrations (zinc, cadmium, exfoliated graphene or nanosilic). . The PS / DMF solution rates used were 33 pL / min for nanoparticles without nanoparticles and 17 pL / min for nanoparticle doped nanomembranes.
a) Grupos 01 e 02  a) Groups 01 and 02
No grupo 01 , foi utilizada a proporção de 20% em peso de poliestireno e 80% em peso de DMF. Já no grupo 02, utilizou-se 35% em peso de poliestireno e 65% em peso de DMF.  In group 01, the proportion of 20 wt% polystyrene and 80 wt% DMF was used. In group 02, 35 wt% polystyrene and 65 wt% DMF were used.
b) Grupo 03  b) Group 03
Foi utilizada a proporção 20% em peso de PS e 80% em peso de DMF. Para esse grupo, adicionou-se o grafeno esfoliado na proporção de 0,5% em massa, com a finalidade de evitar o aumento da viscosidade da nanomembrana.  The ratio 20 wt% PS and 80 wt% DMF were used. For this group, the exfoliated graphene was added in the proportion of 0.5% by mass, in order to avoid the increase of nanomembrane viscosity.
c) Grupos 04 e 05  c) Groups 04 and 05
Foi utilizada a proporção 20% em peso de PS e 80% em peso de DMF. Para esse grupo, adicionou-se a nanosílica esfoliada na proporção de 0,5% em peso para o grupo 04, e 1 ,0% em peso para o grupo 05.  The ratio 20 wt% PS and 80 wt% DMF were used. For this group, the exfoliated nanosilicide was added at 0.5 wt% for group 04 and 1.0 wt% for group 05.
d) Grupo 06  d) Group 06
Foi utilizada a proporção 20% em peso de PS e 80% em peso de DMF, e 5,0% em peso de CdS.  The ratio 20 wt% PS and 80 wt% DMF, and 5.0 wt% CdS were used.
e) Grupos 07, 08 e 09  e) Groups 07, 08 and 09
Foi utilizada a proporção 20% em peso de PS e 80% em peso de DMF. Para esse grupo, adicionou-se as proporções de 5,0% em peso de ZnS para o grupo 07, 10% e 15% em peso de ZnS respectivamente para os grupos 08 e 09. A tabela 1 resume cada conjunto de experiências realizadas e o parâmetro principal no que diz respeito ao processo de eletrofiação. A densidade do campo elétrico aplicado à técnica de eletrofiação foi mantida constante e igual a 150 KV/m em todos os nove conjuntos de experimentos. A tabela 1 mostra, também, as concentrações dos reagentes e as suas taxas de fluxo. The ratio 20 wt% PS and 80 wt% DMF were used. For this group, the proportions of 5.0 wt% ZnS were added for group 07, 10% and 15 wt% ZnS respectively for groups 08 and 09. Table 1 summarizes each set of experiments performed and the main parameter with regard to the process of electroporation. The electric field density applied to the electrophony technique was kept constant and equal to 150 KV / m in all nine sets of experiments. Table 1 also shows the reagent concentrations and their flow rates.
Tabela 1 . Concentração dos reagentes e taxa de fluxo, utilizadas no processo de eletrofiação.  Table 1 Concentration of reagents and flow rate used in the electroporation process.
Figure imgf000018_0001
A Figura 1 mostra os valores das viscosidades dinâmicas para cada conjunto de experiências realizadas. Como pode ser observado, com o aumento da rotação (altas taxas de cisalhamento), a viscosidade dinâmica diminui. No entanto, como comentado por Guerrini e colaboradores, durante os processos de eletrofiação pequenas taxas de cisalhamento são desenvolvidas devido à reduzida taxa de fluxo (Guerrini, L.M. et al. Electrospinning and Characterization of Polyamide 66 Nanofibers with Different Molecular Weights. Materials Research, 181 -190, 2009). Assim, como o valor da viscosidade dinâmica para o grupo 02 é mais elevada do que as dos outros grupos, a sua taxa de fluxo foi aumentada para manter a mesma força eletrostática em todos os casos. A mesma taxa de fluxo foi usada para o grupo 01 para fins de comparação. EXEMPLO 3 - Investigação da influência da morfologia e hidrofobicidade das nanomembranas de poliestireno através da adição das nanopartículas (Grupos 01 a 09)
Figure imgf000018_0001
Figure 1 shows the dynamic viscosity values for each set of experiments performed. As can be seen, with increasing rotation (high shear rates), the dynamic viscosity decreases. However, as commented by Guerrini et al., During shear processes low shear rates are developed due to reduced flow rate (Guerrini, LM et al. Electrospinning and Characterization of Polyamide 66 Nanofibers with Different Molecular Weights. Materials Research, 181 -190, 2009). Thus, as the dynamic viscosity value for group 02 is higher than those of the other groups, its flow rate has been increased to maintain the same electrostatic force in all cases. The same flow rate was used for group 01 for comparison purposes. EXAMPLE 3 - Investigation of the influence of morphology and hydrophobicity of polystyrene nanomembranes by the addition of nanoparticles (Groups 01 to 09)
Para estabelecer uma base de comparação, todos os parâmetros operacionais de eletrofiação (vazão, tensão aplicada, razão) foram baseados em experimentos segundo Ko and Gandhi, 2007 e foram mantidos constantes.  In order to establish a basis of comparison, all the electropower operating parameters (flow, applied voltage, ratio) were based on experiments according to Ko and Gandhi, 2007 and were kept constant.
Um resumo de todos os valores de ângulo de contato com a água (CA) é mostrado na Figura 2. A análise estatística (teste de Levene) indica que todos os nove conjuntos são significativamente diferentes para um p-valor crítico de 0,05. As grandes variações nas medidas de CA poderiam ser devidas à distribuição aleatória das fibras que criam uma superfície irregular. Conforme a hidrofobicidade na interface gotícula de água-nanomembrana aumenta, o desvio padrão de medições de CA diminuem. Como pode ser notado, o grupo 01 apresentou um maior CA (147,96 ± 8,51 )° do que o grupo 02 (143,01 ± 7,88) °. Isto pode ser devido ao aumento da viscosidade, como mostrado na Figura 1 , que pode conseguir reter o solvente residual (DMF) na superfície das fibras. Nota-se que, de acordo com Lee e colaboradores, DMF tem uma tensão superficial de 44 mN/m, enquanto a tensão superficial PS relatados por Shimizu e Demarquette é cerca de 30,3 mN/m. (Lee, K. H. et al. Influence of a Mixing Solvent with Tetrahydrofuran and Ν,Ν-Dimethylformamide on Electrospun Poly(vinyl chloride) Nonwoven Mats. Journal of Polymer Science: Part B: Polymer Physics, 2259-2268, 2002; Shimizu, R.N; Demarquette, N.R. Evaluation of Surface Energy of Solid Polymer using Different Models. Journal of Applied Polymer Science, 1831 -1845, 2000). a) Grupo 01 e 02: Nanomembranas de PS/DMF  A summary of all water contact angle (AC) values are shown in Figure 2. Statistical analysis (Levene's test) indicates that all nine sets are significantly different to a critical p-value of 0.05. The large variations in AC measurements could be due to the random distribution of fibers that create an uneven surface. As hydrophobicity at the water-nanomembrane droplet interface increases, the standard deviation of AC measurements decreases. As can be seen, group 01 had a higher AC (147.96 ± 8.51) ° than group 02 (143.01 ± 7.88) °. This may be due to the increase in viscosity, as shown in Figure 1, which may be able to retain residual solvent (DMF) on the fiber surface. Note that, according to Lee and colleagues, DMF has a surface tension of 44 mN / m, while the surface tension PS reported by Shimizu and Demarquette is about 30.3 mN / m. (Lee, KH et al. Influence of a Solvent Mixing with Tetrahydrofuran and Ν, Ν-Dimethylformamide on Electrospun Poly (vinyl chloride) Nonwoven Mats. Journal of Polymer Science: Part B: Polymer Physics, 2259-2268, 2002; Shimizu, RN Demarquette, NR Evaluation of Surface Energy of Solid Polymer using Different Models (Journal of Applied Polymer Science, 1831-1845, 2000). a) Group 01 and 02: PS / DMF nanomembranes
A imagem obtida em Microscopia Óptica de Varredura (SEM) para o grupo 01 (Figura 3) mostra fibras dispersas numa orientação aleatória. Tal orientação faz com que existam muitos locais onde o ar possa ser preso, o que pode levar a hidrofobicidade considerando o modelo Cassie. De acordo com Carré, isso se deve a baixa energia de superfície do PS (CARRÉ, A. Polar Interactions at Liquid/Polymer Interfaces. J. Adhes. Sei. Tech, 21 (10):961 -981 , 2007). O ângulo de contato da água de (144 ± 4)° pode ser explicado por uma combinação dos modelos, Cassie e Wenzel, já que parece ser praticamente impossível a gota de água ficar completamente "sentada" sob uma bolha de ar. Segundo Cheng e Rodak, um ângulo de contato da água em torno deste valor tipifica uma superfície hidrofóbica (CHENG, Y.T; RODAK, D.E. "Is the Lotus leaf Superhydrophobic?" Applied Physics Letters, 86(14):144101 -03, 2005.). The Scanning Optical Microscopy (SEM) image for group 01 (Figure 3) shows scattered fibers in a random orientation. Such orientation means that there are many places where air can be trapped, which can lead to hydrophobicity considering the Cassie model. According to Carré, this is due to the low surface energy of PS (CARRÉ, A. Polar Interactions at Liquid / Polymer Interfaces. J. Adhes. Sci. Tech, 21 (10): 961-981, 2007). The water contact angle of (144 ± 4) ° can be explained by a Cassie and Wenzel, as it seems almost impossible for a drop of water to be completely "sitting" under an air bubble. According to Cheng and Rodak, a water contact angle around this value typifies a hydrophobic surface (CHENG, YT; RODAK, DE "Is the Lotus leaf Superhydrophobic?" Applied Physics Letters, 86 (14): 144101 -03, 2005. ).
Como pode ser observada na Figura 4, uma gota de água de 0,5 ml_ está "encaixada" sob um grande número de nanofibras e bolhas de ar. Alguns feixes de nanofibras são visíveis perto da base da gota de água. Além disso, as fibras eletrofiadas têm um diâmetro médio de (3,51 ± 0,62)pm. A alta ampliação da imagem em microscopia SEM destas fibras revela uma superfície rugosa que também pode contribuir para a hidrofobicidade (Figura 5). Este padrão de superfície pode ser devido à evaporação de DMF durante a eletrofiação. b) Grupo 03: Nanomembrana de PS/D F/grafeno  As can be seen in Figure 4, a 0.5 ml drop of water is "nested" under a large number of nanofibers and air bubbles. Some bundles of nanofibers are visible near the base of the water droplet. In addition, the spun fibers have an average diameter of (3.51 ± 0.62) pm. High magnification of the SEM microscopy image of these fibers reveals a rough surface that may also contribute to hydrophobicity (Figure 5). This surface pattern may be due to evaporation of DMF during electroporation. b) Group 03: PS / D F / Graphene nanomembrane
As medições dos ângulos de contato de água mostraram um valor médio de (153 ± 5,35)°, o qual é considerado super-hidrofóbico (Figura 6). Este comportamento deve-se ao aumento da condutividade elétrica da solução PS/DMF e, consequentemente, uma diminuição no diâmetro das fibras. Diâmetros de fibra menores (2,08 ± 0,30)pm geram mais locais para o aprisionamento de ar (Figura 7). Também é possível observar alguns acúmulos de grafeno dentro das nanofibras (fibras de expansão súbita). Além disso, a porosidade das nanofibras parece ser afetada pela dispersão de grafeno. A Figura 8 mostra uma grande ampliação da nanomembrana de PS/DMF/grafeno. Novamente, essas irregularidades/rugosidades das superfícies parecem trabalhar a favor da hidrofobicidade. Embora os resultados possam sugerir que o aumento das concentrações de grafeno possam gerar valores ainda melhores de CA, existe uma desvantagem em relação ao uso de altas concentrações dessa nanopartícula. Devido à baixa densidade do grafeno (<0,5 g/cm3 na forma pulverizada,"pó"), um aumento da sua percentagem em peso irá produzir um grande aumento da viscosidade da solução. Assim, para obtenção da membrana super-hidrofóbica, o peso de 0,5 % em peso de grafeno é o limite máximo a ser utilizado no preparo das soluções PS/DMF em 20/80% m/m. c) Grupo 04 e 05: Nanomembranas de PS/DMF/nanosilica Measurements of water contact angles showed an average value of (153 ± 5.35) °, which is considered superhydrophobic (Figure 6). This behavior is due to the increase in electrical conductivity of the PS / DMF solution and, consequently, a decrease in fiber diameter. Smaller fiber diameters (2.08 ± 0.30) pm generate more air trap locations (Figure 7). It is also possible to observe some accumulations of graphene within the nanofibers (sudden expanding fibers). In addition, the porosity of nanofibers appears to be affected by graphene dispersion. Figure 8 shows a large magnification of PS / DMF / graphene nanomembrane. Again, these surface roughness / roughness seems to work in favor of hydrophobicity. Although the results may suggest that increasing graphene concentrations may generate even better AC values, there is a disadvantage compared to the use of high concentrations of this nanoparticle. Due to the low density of graphene (<0.5 g / cm 3 in powdered form, "powder"), an increase in its weight percent will produce a large increase in solution viscosity. Thus, to obtain the superhydrophobic membrane, the weight of 0.5% by weight of graphene is the upper limit to be used in the preparation of the PS / DMF solutions at 20/80% w / w. c) Group 04 and 05: PS / DMF / nanosilica nanomembranes
A porcentagem em peso de nanosílica utilizada foi de 0,5% para o grupo 04 e 1 ,0% em peso para o grupo 05. O ângulo de contato da água (CA) obtido foi de (149,79 ± 7,85)° para o grupo 04 e (153,09 ± 6,58)° para o grupo 05. Há um pequeno decréscimo dos valores de CA quando comparado com as amostras com grafeno, mas, maior do que a solução de PS/DMF sem adição da nanopartícula. A Figura 9 mostra a gota de água "sentada" em feixes de fibras de nanosílica. Esta superfície super-hidrofóbica é o resultado de um processo de dobra dupla. Como pode ser vista na Figura 10, a dispersão de nanosílica em solução PS/DMF levou a menores diâmetros de fibras (2,95 ± 0,44)μιτι, que são maiores do que aquele com o grafeno, mas menores do que o de PS/DMF sem nanopartícula. Além disso, a rugosidade da superfície da fibra foi aumentada pela presença de nano-poros e nanosílica na superfície, como mostrado na Figura 11. A presença de nanosílica sobre a superfície externa das nanofibras é uma indicação da incompatibilidade química entre o solvente e a nanosílica em si.  The percentage by weight of nanosilic used was 0.5% for group 04 and 1.0% by weight for group 05. The contact angle of water (AC) obtained was (149.79 ± 7.85). ° for group 04 and (153.09 ± 6.58) ° for group 05. There is a slight decrease in CA values when compared to graphene samples, but higher than PS / DMF solution without addition of the nanoparticle. Figure 9 shows the drop of water "sitting" on bundles of nanosilica fibers. This superhydrophobic surface is the result of a double fold process. As seen in Figure 10, the dispersion of nanosilica in PS / DMF solution led to smaller fiber diameters (2.95 ± 0.44) μιτι, which are larger than graphene but smaller than PS / DMF without nanoparticle. In addition, the surface roughness of the fiber was increased by the presence of nano pores and nanosilic on the surface, as shown in Figure 11. The presence of nanosilic on the outer surface of nanofibers is an indication of the chemical incompatibility between solvent and nanosilic. in itself.
d) Grupo 06: Nanomembrana de PS/DMF/CdS  d) Group 06: PS / DMF / CdS nanomembrane
Sulfeto de cádmio (CdS) em 5% em peso foi disperso na solução de PS/DMF. Os mesmos parâmetros operacionais de eletrocirculação foram aplicados, entretanto a taxa de fluxo foi de cerca de 1 ,0 mLVh, metade da dos anteriores.  Cadmium sulfide (CdS) at 5 wt% was dispersed in the PS / DMF solution. The same electrocirculation operating parameters were applied, however the flow rate was about 1.0 mLVh, half of the previous ones.
O ângulo de contato da água para a superfície de PS/DMF/CdS foi de (152 ± 7)°, muito próximo ao medido para a superfície de PS/DM F/nanosílica. A Figura 12 mostra a gota de água "encaixada" nesta superfície super- hidrofobica. Embora o ângulo de contato da água fosse quase o mesmo, a gota de água, neste caso foi de 2,0 ml_. Ainda, de acordo com Lafuma e Quéré, (2003) gotas maiores de água podem ser achatadas por gravidade. Uma possível explicação para a presença de grandes gotas de água esféricas é a existência de nanofibras ao redor da base da gota de água. Esta hipótese pode ser corroborada por observações em microscopia SEM. Na Figura 13, além das nanopartículas de sulfeto de cádmio dentro das nanofibras, alguns agrupamentos de sulfeto de cádmio (partículas brancas brilhantes) podem ser vistos entre as fibras. O diâmetro médio da fibra foi de (2,32 ± 0,35) pm. A diminuição do diâmetro das fibras pode ser devido ao melhoramento da condutividade elétrica da solução de PS/DMF. Outro fator que provavelmente contribuiu para a super-hidrofobicidade foi a rugosidade da superfície das fibras. Novamente, aglomerados de nanopartículas, foram localizados fora das fibras e, até mesmo, parcialmente envolvidos pelas nanofibras de PS (Figura 14). The water contact angle for the PS / DMF / CdS surface was (152 ± 7) °, very close to that measured for the PS / DM F / nanosilicon surface. Figure 12 shows the drop of water "fitted" to this superhydrophobic surface. Although the contact angle of the water was almost the same, the drop of water in this case was 2.0 ml. Also, according to Lafuma and Quéré, (2003) larger drops of water can be flattened by gravity. A possible explanation for the presence of large spherical water droplets is the existence of nanofibers around the base of the water droplet. This hypothesis can be corroborated by observations in SEM microscopy. In Figure 13, in addition to cadmium sulfide nanoparticles within nanofibers, some cadmium sulfide clusters (bright white particles) can be seen between the fibers. The average fiber diameter was (2.32 ± 0.35) pm. The decrease in fiber diameter may be due to improved electrical conductivity of the PS / DMF solution. Another factor that probably contributed to the superhydrophobicity was the surface roughness of the fibers. Again, clumps of nanoparticles were located outside the fibers and even partially enveloped by the PS nanofibers (Figure 14).
e) Grupos 07, 08 e 09: Nanomembranas de PS/DMF/ZnS  e) Groups 07, 08 and 09: PS / DMF / ZnS nanomembranes
Adicionou-se ZnS (sulfeto de zinco) 5% em peso a uma taxa de fluxo de 1 ,0 mL/h. Semelhantemente às outras experiências, todos os outros parâmetros operacionais de eletrofiação foram mantidos constantes.  5 wt% ZnS (zinc sulfide) was added at a flow rate of 1.0 mL / h. Similar to other experiments, all other electropower operating parameters were kept constant.
Uma análise sobre os grupos 06 a 09 revelaram um aumento não-linear nos valores de CA. A adição de ZnS originou diferentes valores de CA: (153,20 ± 7,47) °, (163,49 ± 4,93)° e (168,22 ± 3,19)° para 5% m/m, 10% m/m e 15% m/m, respectivamente. O diâmetro médio das fibras foi de (1 ,82 ± 0,45) pm. Este padrão pode ser atribuído às nanopartículas, principalmente situadas em tomo da superfície das fibras (Figuras 15, 16 e 17). As variações nos diâmetros das nanofibras devido as adições de cádmio (284,39 ± 8,71 )nm e zinco (323,34 ± 6,98)nm e das distribuições das fibras poderiam ser a razão para as diferenças nos valores de CA. O aumento adicional de CA para grupos 08 e 09 pode ser devido à aglomeração de nanopartículas de Zn através das paredes das nanofibras de PS. Estes aglomerados são da ordem de (378,92 ± 8,78)nm para adição de ZnS 10% m/m (grupo 08) e (561 ,31 ± 11 ,94)nm para a adição de ZnS 15% m/m (grupo 09), respectivamente. Com o aumento da concentração das nanopartículas de zinco, a rugosidade obtida na superfície da fibra torna-se maior e, consequentemente, um maior valor de CA é obtido. Finalmente, a Figura 18 mostra uma gota de água sobre a superfície a partir do grupo 09. Com base nos valores obtidos de CA, é possível categorizar o grupo 09 (adição de 15% m/m de ZnS) como nanomembranas hiper-hidrofóbicas. Tabela 2. Valores de CA's obtidos para os diferentes grupos. Grupo de Teste Agente Dopante (%) CA (°) An analysis of groups 06 to 09 revealed a nonlinear increase in AC values. Addition of ZnS gave different CA values: (153.20 ± 7.47) °, (163.49 ± 4.93) ° and (168.22 ± 3.19) ° to 5% w / w, 10 % m / m and 15% m / m, respectively. The average fiber diameter was (1.82 ± 0.45) pm. This pattern can be attributed to nanoparticles, mainly located around the fiber surface (Figures 15, 16 and 17). Variations in nanofiber diameters due to cadmium (284.39 ± 8.71) nm and zinc (323.34 ± 6.98) nm additions and fiber distributions could be the reason for differences in CA values. The additional increase in CA for groups 08 and 09 may be due to agglomeration of Zn nanoparticles through the walls of PS nanofibers. These agglomerates are of the order of (378.92 ± 8.78) nm for the addition of 10% w / w ZnS (group 08) and (561.31 ± 11.94) nm for the addition of 15% w / w ZnS (group 09), respectively. With increasing concentration of zinc nanoparticles, the roughness obtained on the fiber surface becomes larger and consequently a higher CA value is obtained. Finally, Figure 18 shows a drop of water on the surface from group 09. Based on the obtained CA values, it is possible to categorize group 09 (addition of 15% w / w ZnS) as hyperhydrophobic nanomembranes. Table 2. AC values obtained for the different groups. Doping Agent Test Group (%) CA (°)
(percentagem em peso)  (percentage by weight)
01 Não 147,96±8,51  01 No 147.96 ± 8.51
02 Não 143,01±7,88  02 No 143.01 ± 7.88
03 0,5 em grafeno 152,09±5,35  03 0.5 in graphene 152.09 ± 5.35
04 0,5 em nanosílica 149,79±7,85  04 0.5 in nanosilic 149.79 ± 7.85
05 1 ,0 em nanosílica 153,09±6,58  05 1.0 on nanosilica 153.09 ± 6.58
06 5,0 em CdS 151 ,22±6,80  06 5.0 at CdS 151, 22 ± 6.80
07 5,0 em ZnS 153,20±7,47  07 5.0 in ZnS 153.20 ± 7.47
08 10,0 em ZnS 163,49±4,93  08 10.0 in ZnS 163.49 ± 4.93
09 15,0 em ZnS 168,22±3,19  09 15.0 in ZnS 168.22 ± 3.19
Como descrito por Antonini e colaboradores, superfícies super-hidrofóbicas têm energia de superfície pequena, que levam a forças de adesão pequenas (Antonini, C. et al. Understanding the Effect of Superhydrophobic Coating on Energy Reduction in Anti-lcing Systems. Cold Regions Science and Technology, 58-67, 201 1 ). A Figura 19 mostra a energia superficial, considerando o modelo de Neumann para cada conjunto de membranas testadas. Além disso, como relado por Tourkine e colaboradores também há um atraso no congelamento quando materiais repelentes de água são empregados (Tourkine, P. et al. Delayed Freezing on Water Repellent Materials. Langmuir Letter, 7214-7216, 2009). Nos experimentos descritos nesse pedido, uma gota de água de 10 μΙ_ ainda estava em forma líquida a -7°C (Figura 20 ). Este fenómeno pode ser explicado com a quantidade de ar aprisionado no interior da membrana, a qual funciona como uma barreira térmica. As described by Antonini et al., Superhydrophobic surfaces have small surface energy, which leads to small adhesion forces (Antonini, C. et al. Understanding the Effect of Superhydrophobic Coating on Energy Reduction in Anti-Systems. Cold Regions Science and Technology, 58-67, 2011). Figure 19 shows the surface energy, considering the Neumann model for each set of membranes tested. In addition, as reported by Tourkine and colleagues there is also a delay in freezing when water repellent materials are employed (Tourkine, P. et al. Delayed Freezing on Water Repellent Materials. Langmuir Letter, 7214-7216, 2009). In the experiments described in this application, a 10 μΙ_ drop of water was still in liquid form at -7 ° C (Figure 20). This phenomenon can be explained by the amount of air trapped inside the membrane, which acts as a thermal barrier.
De acordo com Garcia-Cordiovilla e colaboradores a tensão de superfície de uma superfície de alumínio é cerca de 1 100 MJ/m2, quatro ordens de grandeza maior do que o apresentado pelo grupo 09, que foi de cerca de 0,03 MJ/m2 (Garcia-Cordiovilla, C. et al. The Surface Tension of Liquid Pure Aluminum and Aluminum-Magnesium Alloy. Journal of Materials Science, 2787- 2792, 1986). According to Garcia-Cordiovilla and colleagues, the surface tension of an aluminum surface is about 1,100 MJ / m 2 , four orders of magnitude higher than that of group 09, which was about 0.03 MJ / m 2 . m 2 (Garcia-Cordiovilla, C. et al. The Surface Tension of Liquid Pure Aluminum and Aluminum-Magnesium Alloy. Journal of Materials Science, 2787-2792, 1986).

Claims

REIVINDICAÇÕES
1- Processo de preparação de nanomembranas super-hidrofóbicas, caracterizado por compreender as seguintes etapas:  Process for preparing superhydrophobic nanomembranes, comprising the following steps:
a- Dissolução do polímero, preferencialmente o poliestireno, em solvente orgânico, com concentração entre 20 e 35% m/m sob agitação a temperatura de 40°C, preferencialmente;  Dissolving the polymer, preferably polystyrene, in an organic solvent, with a concentration between 20 and 35% w / w under stirring at 40 ° C, preferably;
b- Resfriamento a temperatura entre 20 e 25°C;  b- Cooling at a temperature between 20 and 25 ° C;
c- Adição das nanopartículas, metálicas ou não, e agitação da solução através do uso de um sonicador, preferencialmente a 20 KHz, durante um período de tempo entre 30 a 60 minutos;  c) Addition of the nanoparticles, metallic or not, and stirring of the solution by the use of a sonicator, preferably at 20 KHz, for a period of 30 to 60 minutes;
d- Eletrofiaçao da solução obtida em "c".  d- Electrophytion of the solution obtained in "c".
2- Processo de preparação de nanomembranas super-hidrofóbicas, de acordo com a reivindicação 1 , etapa "a", caracterizado pelo solvente orgânico utilizado ser: tolueno, clorofórmio, ciclohexano, dimetil sulfóxido (DMSO), tetrahidrofurano (THF), preferencialmente dimetilformamida (DMF), ou a mistura desses. Process for the preparation of superhydrophobic nanomembranes according to claim 1, step "a", characterized in that the organic solvent used is: toluene, chloroform, cyclohexane, dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), preferably dimethylformamide ( DMF), or the mixture thereof.
3- Processo de preparação de nanomembranas super-hidrofóbicas, de acordo com a reivindicação 1 , etapa "c", caracterizado pelas nanopartículas, metálicas ou não, serem selecionadas do grupo compreendendo sulfeto de cádmio, sulfeto de zinco, grafeno e nanosílica. Process for the preparation of superhydrophobic nanomembranes according to claim 1, step "c", characterized in that nanoparticles, metallic or not, are selected from the group comprising cadmium sulfide, zinc sulfide, graphene and nanosilicon.
4- Processo de preparação de nanomembranas super-hidrofóbicas, de acordo com a reivindicação 1, etapa "c", caracterizado pela concentração das nanopartículas serem de 0,1 a 20% m/m, sendo que, preferencialmente a concentração de nanopartículas de grafeno não excede 0,5% m/m; a concentração da nanosílica está compreendida entre 0,5 e 1 % m/m; a concentração da nanopartícula de sulfeto de cádmio não excede 5% m/m; e a concentração da nanopartícula de sulfeto de zinco está compreendida entre 5 e 15% m/m. Process for preparing superhydrophobic nanomembranes according to claim 1, step "c", characterized in that the concentration of the nanoparticles is from 0.1 to 20% w / w, preferably the concentration of graphene nanoparticles does not exceed 0.5% w / w; the nanosilic concentration is between 0.5 and 1% w / w; cadmium sulfide nanoparticle concentration does not exceed 5% w / w; and the concentration of zinc sulfide nanoparticle is between 5 and 15% w / w.
5- Processo de preparação de nanomembranas super-hidrofóbicas, de acordo com a reivindicação 1 , etapa "e", caracterizado pela eletrofiação da solução obtida em "c" utilizar, preferencialmente, um fluxo entre 17 e 33 pl_/h a uma tensão aplicada de 15 KV, densidade de campo elétrico aplicado de 150 KV/m e distância entre a extremidade da agulha e a placa preferencialmente de 10 cm. Process for preparing superhydrophobic nanomembranes according to claim 1, step "e", characterized in that the electrophony of the solution obtained in "c" preferably uses a flow between 17 and 33 pl_ / ha an applied voltage of 15 KV, applied electric field density 150 KV / m and the distance between the needle end and the plate preferably 10 cm.
6- Nanomembrana super-hidrofóbica, caracterizada por compreender o polímero, preferencialmente o poliestireno, numa faixa de concentração entreSuperhydrophobic nanomembrane, characterized in that it comprises the polymer, preferably the polystyrene, in a concentration range between
20 a 35% m/m, dissolvido em um solvente orgânico e dopado com nanopartículas, metálicas ou não, resultantes do processo das reivindicações 1 a 5. 20 to 35% w / w, dissolved in an organic solvent and doped with nanoparticles, metallic or not, resulting from the process of claims 1 to 5.
7- Nanomembrana super-hidrofóbica, de acordo com a reivindicação 6 caracterizada por apresentar fibras com diâmetro médio, preferencialmente entre 1 ,37 a 4,13 μιη. Superhydrophobic nanomembrane according to Claim 6, characterized in that it has fibers of average diameter, preferably between 1.37 and 4.13 μιη.
8- Nanomembrana super-hidrofóbica, de acordo com a reivindicação 6, caracterizada por apresentar a superfície irregular com pontos de ranhura descontínuas variando, preferencialmente, entre 1 15 a 125 nm de comprimento e 6,2 a 7,8 nm de largura. Superhydrophobic nanomembrane according to claim 6, characterized in that it has an irregular surface with discontinuous groove points preferably ranging from 1115 to 125 nm in length and 6.2 to 7.8 nm in width.
9- Nanomembrana super-hidrofóbica, de acordo com a reivindicação 7 caracterizada por apresentar o ângulo de contato com a água (CA) entre 150 a 172°. Superhydrophobic nanomembrane according to claim 7, characterized in that the contact angle with water (CA) is between 150 and 172 °.
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