CN111019473A

CN111019473A - Preparation of coatings with excellent mechanical and chemical stability

Info

Publication number: CN111019473A
Application number: CN201911348771.9A
Authority: CN
Inventors: 刘利彬; 张海龙; 李学林; 郑良; 任金瓶
Original assignee: Qilu University of Technology
Current assignee: Qilu University of Technology
Priority date: 2019-12-24
Filing date: 2019-12-24
Publication date: 2020-04-17
Anticipated expiration: 2039-12-24
Also published as: CN111019473B

Abstract

The invention relates to the preparation of coatings with excellent mechanical and chemical stability, suspensions of Silica (SiO) grafted with 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane (FAS)₂) And α -cellulose and hexafluorobutyl acrylate (HFBA) as a binder monomer (FIG. 1 a.) the present application produces a super-amphiphobic coating by a spray coating process that is low cost and can be mass producedSurface energy of only 12.98mN m^‑1. Can reduce the surface tension to 21mN m^‑1And various organic liquids having a viscosity as high as 297.8mPa s rebound. The coating can be applied to different substrates due to the in situ formed binder and subjected to high pressure water impingement (27.8m s)^‑1) The adhesive tape shows excellent performance in abrasion and tape stripping tests, and can maintain excellent performance in high-corrosivity aqua regia, extreme low/high temperature and severe environments such as ultraviolet irradiation.

Description

Preparation of coatings with excellent mechanical and chemical stability

Technical Field

The invention belongs to the field of preparation of super-amphiphobic coatings, and particularly relates to a multifunctional and mechanochemical stable super-amphiphobic coating which is sprayed by low-cost suspension liquid and can make organic liquid drops bounce and can be industrialized.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The super-amphiphobic surface for repelling water drops and oil drops is a special anti-wetting state in the field of interface science, and has wide application in the fields of droplet manipulation, self-cleaning, heat transfer, anti-icing, liquid-liquid separation and the like. The study of super-amphiphobic surfaces has been continuously updated since the first oil droplet repellent surfaces were manufactured in 1997. For industrial production, the use of low-cost raw materials and simple production processes should be considered. For achieving super-amphiphobicity of a surface, a rough surface and a low surface energy material are required, but the mechanism for structuring a super-amphiphobic surface is still unclear. Due to organic liquid (20-50mN m)^-1) Is much lower than that of water (72.2mN m)^-1) And thus it is very difficult to manufacture a super-amphiphobic surface having a Contact Angle (CA) of the organic liquid of more than 150 ° and a Sliding Angle (SA) of less than 10 °. The required morphology and structure for designing a super-amphiphobic material is more complex. In view of this, the reentrant structure proposed by Tuteja et al, Liu and Kim in 2007 proposed a dual entry structure that provided valuable guidance for the development of a super-amphiphobic coating. However, the manufacturing process of these different multi-level micro/nano structures is complex and energy consuming, e.g. the use of pure gas in liquid flame is required in the manufacturing process of super-amphiphobic structures: (E.g., oxygen, methane or hydrogen), etching in photolithographic processes and templating have all limited commercial production that can be produced on a large scale.

In addition to a simple manufacturing process, another requirement for the practical application of the super-amphiphobic materials is that the coatings possess good properties. The superamphiphobic materials should not only be completely repellent to liquids (water and various organic liquids), but also have good mechanical and chemical stability, and more importantly, the droplets can roll or rebound on their surface. The super-amphiphobic coating at the present stage has weaker mechanical strength with the interface. Enhancing interfacial adhesion strength requires polar groups to interact with the substrate, but the addition of polar groups will inevitably consume the lyophobicity of the coating. The reported super-amphiphobic coatings have only low adhesive strength and lack robustness. In contrast, most good durable droplet-repellent surfaces are generally superhydrophobic coatings, but they can only repel water droplets completely. It is important to select a suitable binder in view of the fact that an increase in the adhesive strength reduces the lyophobicity of the coating. In addition, liquid bounce is an important indicator for characterizing superamphiphobic performance. To date, research on droplet bounce has focused primarily on super-hydrophobic surfaces, while much less has been explored on the bouncing mechanics of organic droplets on super-amphiphobic surfaces. A coating with excellent properties has been recently reported to not only have an excellent repulsive force to solvents, acids and bases, but also rebound a liquid with a very low surface tension. However, dichloropentafluoropropane is used as a solution in the production process, and is highly corrosive. Therefore, it remains a great challenge to produce a super-amphiphobic material with good properties by simple, inexpensive materials and methods.

Disclosure of Invention

To overcome the above problems, the present invention provides a multifunctional, mechanochemical stable, industrially applicable super-amphiphobic coating for bouncing organic droplets by low cost suspension spraying. The super-amphiphobic coating is prepared by a low-cost and large-scale preparation method. Suspensions of Silica (SiO) grafted with 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane (FAS)₂) And α -celluloseAnd hexafluorobutyl acrylate (HFBA) as a binder monomer (a in fig. 1). By spraying, super-amphiphobic coatings with multi-level micro/nano roughness structures can be applied to different substrates (e.g. iron sheet, ceramic tile, wood and cotton fabrics). Adhesives formed by HFBA in situ self-polymerization (poly-HFBA) provide coatings with excellent mechanical and chemical durability, e.g., resistance to high velocity liquid impact, abrasion, aqua regia corrosion, high/low temperature environments. Importantly, the coating can repel surface tensions as low as 21mN m^-1And various organic liquids having a viscosity of up to 297.8mPa s. More importantly, the organic liquid bouncing dynamics were also studied in relation to impact velocity and the inherent properties of the liquid (viscosity, surface tension and density).

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

a preparation method of a super-amphiphobic coating comprises the following steps:

mixing SiO₂Dispersing the nano-particles and α -cellulose in an ethanol/ammonia water solution, then sequentially dropwise adding tetraethyl silicate and 1H, 1H, 2H, 2H-perfluorodecyl trimethoxy silane for hydrolysis, and adding the mixture into SiO₂Nanoparticle and α -cellulose coated with SiO₂；

Tetraethyl silicate and 1H, 1H, 2H, 2H-perfluorodecyl trimethoxy silane are added into a solvent system at one time to react to generate polysiloxane, so that suspension is formed;

and adding hexafluorobutyl acrylate into the suspension for self-polymerization reaction, and spraying to obtain the super-amphiphobic coating.

The present application utilizes tetraethyl silicate to successively pair SiO₂SiO of nanoparticle and α -cellulose mixture₂Coating and polysiloxane generation are carried out to construct a micro-nano structure with multi-level roughness, and the micro-nano structure is matched with an adhesive (poly-HFBA) formed by HFBA in-situ self-polymerization, so that the prepared coating has excellent mechanical and chemical durability, such as high-speed liquid impact resistance, abrasion resistance, aqua regia corrosion resistance and high/low temperature environment resistance. The coating can repel the surface tension as low as 21mN m^-1And various organic liquids having a viscosity of up to 297.8mPa s. More importantly, the organic liquid bounce dynamics and impact are also researchedSpeed and the inherent properties of the liquid (viscosity, surface tension and density).

In some embodiments, the SiO₂The mass ratio of the nano particles to α -cellulose is 2: 3-5, and a short rod-shaped structure of the cellulose is utilized to form SiO₂And (3) loading the nano particles so as to be beneficial to the subsequent construction of a micro-nano structure with multilevel roughness.

In some embodiments, the suspension is SiO₂The concentration of (2) is 30-50 wt% to improve the hardness of the coating and construct a micro-nano structure with multi-level roughness.

In some embodiments, the volume ratio of tetraethyl silicate, 1H, 2H, 2H-perfluorodecyltrimethoxysilane to hexafluorobutyl acrylate is 2-3: 1-1.5: 2. hydrolysis of TEOS can provide SiO at 500nm₂Nanoparticles, FTIR and XPS show that FAS is successfully grafted to SiO by forming Si-O-Si bonds due to the low surface energy of the fluorine chains₂And forms the outermost layer of the coating.

In some embodiments, the conditions for coating are: mechanically mixing the mixture in a water bath at the temperature of 50-55 ℃ for 6-8 h; the polysiloxane is generated under the condition of mechanical mixing in a water bath at 50-55 ℃ for 5-10 min so as to form a micro-nano structure with multi-level roughness.

In some embodiments, the conditions of the self-polymerization reaction are: mechanically mixing for 1.5-3 h at 50-55 ℃; and a uniform coating with high adhesive force is obtained under the condition of not damaging the super-lyophobicity of the coating.

In some embodiments, the spray coating employs a spray gun to spray 2mL of suspension onto a horizontally positioned substrate surface from a distance of 10cm vertically to improve spray efficiency and coating uniformity.

In some embodiments, the coating is dried at 75-90 ℃ for 5-8 hours after the spraying is finished, and the coating is cured to form a surface structure with excellent mechanical and chemical durability.

The invention also provides a super-amphiphobic coating prepared by any one of the methods.

The invention also provides the application of the super-amphiphobic coating in the fields of droplet manipulation, self-cleaning, heat transfer, anti-icing or liquid-liquid separation.

The invention has the beneficial effects that:

(1) the present application produces a super-amphiphobic coating by a spray coating process that is low cost and can be produced on a large scale. The sprayed super-amphiphobic coating can form a multi-stage micro/nano structure with very low surface energy of only 12.98mNm^-1. The coating can reduce the surface tension to 21mN m^-1And various organic liquids having a viscosity as high as 297.8mPa s rebound. More particularly, the coating can be applied to various substrates and subjected to high pressure water impingement (27.8m s) due to the in situ formed binder^-1) The adhesive tape shows excellent performance in abrasion and tape peeling tests, and can maintain excellent performance in high-corrosivity aqua regia, extreme low/high temperature and severe environments such as ultraviolet irradiation. And for the first time the relationship between organic liquid bounce dynamics and impact velocity and liquid properties was discussed. By virtue of the simple preparation method and the excellent properties of the coating, the coating of the present application paves the way for real industrial applications.

(2) The operation method is simple, low in cost, universal and easy for large-scale production.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.

FIG. 1 is a schematic diagram of the preparation process of the super-amphiphobic suspension (a) and the spraying method (b). SEM images of side (c up) and top (c down) views of a super-amphiphobic coating with micron dimensions. (d) High magnification SEM images of coatings with nanometer dimensions. Schematic representation of three different size coatings: (e) FAS grafted SiO₂(15nm and 500nm) and cellulose, (f, up) FAS grafted SiO₂(500nm) and cellulose, (f, down) FAS grafted SiO₂(15nm) and cellulose. The multi-level micro/nano-structure of coating (e) has the best performance among the three coatings and can completely repel the droplets. (g) photographs of yogurt, cola, coffee, n-octane, n-hexadecane and water, respectively standing on coated steel chips, tiles, wood, cotton fabric.

Figure 2. drop bounce experiments. (a) Maximum break-up height of different droplets with a volume of 6. mu.L. (b) Taking n-hexadecane as an example, the whole bouncing process of the liquid drop is adopted, and the yellow area corresponds to the first bouncing process. (c) The contact time of the water and organic liquid released at different heights. The water has the same contact time with the solid surface at different release heights, and the organic liquid has different contact times with the solid surface at different release heights. (d) A photograph of the first bounce process of n-hexadecane. The contact time includes the spreading time (t)_s) And retraction time (t)_r). Maximum spreading diameter (Dmax) at which the droplet spreads to the maximum spreading diameter. The droplets are expressed as v₁Is in contact with the surface at a velocity of v₁The velocity of' is away from the surface. The velocity of the second impact surface is upsilon₂。

FIG. 3 viscosity test. (a) Contact time of three groups of liquids with similar viscosity and different surface tension. (b) Effect of liquid viscosity on contact time. (c) Contact time of different liquids at different weber numbers. (d) Contact time and number of bounces of high viscosity glycerol with viscosity from 25.6 to 154mPa s at different temperatures. (e) Photograph of the bouncing process of a glycerol droplet having a viscosity of 297.8mPas at 40 ℃. The time interval is 8 mm.

FIG. 4 mechanical strength of the super-amphiphobic coating. (a) Schematic representation of the effect of high velocity water impact on the super-amphiphobic coating. (b) The number of bounces of n-hexadecane on the impact surface after different impact times. (c) SEM image of the surface of the coating after water impact for 14 minutes. (d) The coating has a repulsive force to the hot fluid and the change in CA and SA of water, diiodomethane and n-hexadecane after the coating has been impacted for 14 minutes. (e) Abrasion and (f) effect of tape stripping on the performance of the super-amphiphobic coating.

FIG. 5 chemical stability of the super-amphiphobic coating. (a) The effect of aqua regia corrosion time on the coating. (b) SEM image of coated glass after immersion in aqua regia for 60 minutes. (c) The coated glass was treated in low and high temperature environments and the high and low temperature resistance of the coating was examined using CA and SA of n-hexadecane. (d) SEM image of the coating after 6 hours of treatment at 220 ℃.

FIG. 6 application of a super-amphiphobic coating. (a) Photographs of the original boat (left) and the coated boat (right). (b) The original and coated boats were immersed in water and peanut oil to a depth. (c) The original boat, carrying 100 grams, was submerged (top panel) and the coated boat, carrying 360 grams, was floated on the water (bottom panel). (d) The depth of immersion of the original and coated vessels at different loads. (e) Stability on seawater and peanut oil for a coated boat loaded 100 grams. (f) The effect of the coating on anti-icing was investigated by spraying the suspension onto different substrates.

FIG. 7 DLS measurement of superamphiphobic suspensions. 15nm SiO₂And 25 μm cellulose, 500nm SiO₂Particles are formed by TEOS hydrolysis.

FIG. 8 FTIR spectra of superhydrophobic coatings. The band at 1160cm-1 is due to the Si-O-Si band formed by the co-condensation of hydrolyzed TEOS and FAS 1. The band at 1210cm-1 is due to C-F bonds and Si-O groups.

FIG. 9 XPS spectra of superhydrophobic coatings. XPS spectra show that FAS grafted SiO due to the low surface energy of the fluorine chains₂Forming the outermost layer of the coating.

Fig. 10. selection of adhesive. The effect of different mass fractions and different binder selections on the coating adhesion.

FIG. 11 photo of a super-amphiphobic coating on a glass substrate. The coating is formed by making a suspension by self-polymerization of the C ═ C double bond in AIBN initiated by the addition of an initiator (azobisisobutyronitrile, AIBN). After curing, the coating was clearly visible as chapping on the glass substrate.

FIG. 12 HFBA polymerization mechanism, in alkaline suspension, OH^-Can be used as a nucleophile to attack double bonds.

Fig. 13 FTIR spectrum of C ═ C bond in HFBA.

FIG. 14 is an electron micrograph of a blank cellulose.

FIG. 15 is an electron micrograph. SEM images of the superhydrophobic-amphiphobic layers (a) and (b) at different magnifications. The super-amphiphobic coating is mapped to elements of C (c), O (d), F (e), Si (f). It can be seen that multi-level micro/nano structures are formed and four elements of C, F, Si and O are uniformly dispersed on the surface of the coating layer.

FIG. 16. schematic contact Angle (a) α -cellulose and SiO with different mass ratios₂Schematic representation of the contact angles of the coatings (b) SiO of different sizes₂Effect of nanoparticles on coating properties.

FIG. 17. extrapolation of surface energy of superhydrophobic coatings with different micro/nanostructures (a)15nm SiO₂+500nm SiO₂+ α -cellulose (b)15nm SiO₂+ α -cellulose (c)500nm SiO₂+ α -cellulose the liquid used in the extrapolation is water (72.8mN m^-1) Ethylene glycol (48mN m)^-1) Ethylenediamine (42.7mN m)^-1) N, N-dimethylformamide (34.4 mN m)^-1) N-hexadecane (27.1mN m)^-1) N-dodecane (25mN m)^-1) N-octane (21.2mN m)^-1) N-heptane (20.1mN m^-1) N-hexane (17.6 mNm)^-1) N-pentane (15.5mN m)^-1)。

Figure 18. by selecting the effect of three groups of droplets having similar surface tension but different viscosities on contact time, it can be seen that the contact time increases gradually with increasing viscosity.

FIG. 19 abrasion test. (a) Schematic diagram of abrasion test. SEM images at low (b) and high (c) magnification of the coating after 30 wear cycles.

FIG. 20 peeling experiment. (a) Schematic of peel cycle testing. Low (b) and high (c) magnified SEM images of the coating after 30 peel cycles.

FIG. 21 irradiation with n-hexadecane CA and SA was carried out at different times.

Figure 22. blank boat of 100 gram load floating on water and peanut oil.

FIG. 23 compares the time of water freezing on a bare substrate and a coated substrate. It can be clearly seen that the freezing time of water on the original substrate is within 5 minutes. In contrast, the time for water to freeze on the superamphiphobic-coated substrate increases significantly.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The present invention is described in further detail below with reference to specific examples, which are intended to be illustrative of the invention and not limiting.

Example 1:

method of producing a composite material

Preparation of super-amphiphobic coatings

0.4g of SiO are weighed₂(15nm) and 0.6g of α -cellulose (25 μm) and dispersed in a solution of 30mL of absolute ethanol mixed with 10mL of aqueous ammonia and the mixture stirred and sonicated for 20 minutes 2mL of TEOS and 0.6mL of LFAS were added dropwise to the above solution and stirred in a water bath at 50 ℃ for 6h, then 0.6mL of TEOS and 0.6mL of FAS were rapidly injected into the suspension, stirred for 5 minutes, then 2mL of HFBA was added dropwise and stirred at 50 ℃ for a further 2h to give a final homogeneous suspension, 2mL of the suspension was sprayed onto a horizontally placed substrate surface (3cm x 8cm) from a distance of 10cm in the vertical direction using a spray gun (ET4000, STAT, Germany), finally, after drying at 80 ℃ for 6h in a vacuum oven, a super-amphiphobic coating layer coated on the substrate was obtained.

Organic droplet impact process

For the maximum break-up height measurement, droplets (about 2.4mm in diameter) with the same volume were selected. The initial velocity of the drop was 0 and the impact velocity was adjusted by different release heights. In addition, the bounce mechanics was studied by releasing the same volume (6 μ L) of organic liquid at a height of 6 cm. At least ten samples from different areas of the coating were used to measure contact time and maximum fracture height. The liquid bounce process was recorded by a phantom V710L high speed camera (7400fps, Ametek, usa).

Characterization of

Static contact angle and sliding angle were measured by KR ü SSDSA25S (germany) contact angle system at least five samples from different areas of the coating were tested to obtain average values of static contact angle and sliding angle surface morphology was observed by a SUPRA TM 55 thermal field emission scanning electron microscope (SEM, germany) at a working voltage of 5 KV.

Preparation of super-amphiphobic coatings

By adding 15nm SiO to an ethanol/ammonia solution₂Nanoparticles and 25 μm α -cellulose particles, followed by addition of Tetraethylorthosilicate (TEOS) and FAS, to prepare a suspension (a in FIG. 1). The hydrolysis of TEOS, as demonstrated by DLS measurements (FIG. 7), can provide 500nm of SiO₂Nanoparticles, FTIR and XPS show that FAS is successfully grafted to SiO by forming Si-O-Si bonds due to the low surface energy of the fluorine chains₂And forms the outermost layer of the coating (fig. 8 and 9). Another major problem is the adhesion of the coating to the substrate, and the addition of a suitable binder is beneficial for the durability of the coating, but at the expense of ultralyophobicity. By systematically investigating the effect of the binder on the coating properties (see fig. 10), HFBA was chosen as the binder monomer in the present application. It should be noted that the polymerization of HFBA plays an important role in the final properties of the coating. Addition of initiator during HFBA polymerization can cause the coating to crack on the glass substrate (fig. 11). Surprisingly, a uniform coating with high adhesion can be obtained without the use of initiators. The present application therefore guesses that the autopolymerization of the C ═ C group in HFBA occurs due to the strong electron withdrawing group of the hexafluoro chain. OH-in the coating suspension can be used as nucleophile during HFBA polymerization (FIG. 12) to therebyPromoting nucleophilic addition reaction. To demonstrate this, the change in the peak of C ═ C bond was detected by dissolving HFBA in ethanol/aqueous ammonia solution. As shown in fig. 13, at 1730cm over time^-1The peak of the centered C ═ C bond disappeared, indicating OH^-Can be used as nucleophiles for attacking double bonds, the in situ formed poly-HFBA grafting FAS to SiO₂And α -cellulose adheres to the substrate, giving the coating excellent properties.

FIG. 1 is a schematic diagram of the preparation process of the super-amphiphobic suspension (a) and the spraying method (b). SEM images of side (c up) and top (c down) views of a super-amphiphobic coating with micron dimensions. (d) High magnification SEM images of coatings with nanometer dimensions. Schematic representation of three different size coatings: (e) FAS grafted SiO₂(15nm and 500nm) and cellulose, (f, up) FAS grafted SiO₂(500nm) and cellulose, (f, down) FAS grafted SiO₂(15nm) and cellulose. The multi-stage micro/nano-structure of coating (e) has the best performance among the three coatings and can completely repel droplets. (g) photographs of yogurt, cola, coffee, n-octane, n-hexadecane and water, respectively standing on coated steel chips, tiles, wood, cotton fabric.

After spraying the suspension, a multi-scale micro/nano-structure is obtained, which contributes to the super-amphiphobic properties of the coating (b in fig. 1), the side view of the coating shows hilly structures with micrometers (c in fig. 1, up), the top view shows many rough protrusions (c in fig. 1, down), the high magnification SEM image shows that the nano-and micro-scale multi-scale particles are evenly distributed on the substrate (d in fig. 1, original α -SEM image of cellulose is in fig. 14), the elemental map shows that the fluorine chains originating from FAS and HFBA are evenly present on the coating surface (fig. 15), the multi-scale micro/nano-structure is important for lyophobic properties₂Tightly bound to cellulose and firmly adhered by in-situ formed poly-HFBAOn a substrate (b and e in fig. 1). The large amount of air layer in the multi-level micro/nano structure provides the coating with excellent ability to repel organic liquid. To further demonstrate the critical role of the multilevel structure of the coating, two other coatings were prepared from (I) fluorinated SiO₂(-500 nm) and α -cellulose (f in FIG. 1, up) and (II) fluorinated SiO₂(-15 nm) and α -cellulose (f in fig. 1, bottom) the performance of the coating was examined by drop bounce, when only the two classes of micro-nano structures described above were used, dimethylsulfoxide (DMSO, surface tension, γ: 42.7mN m^-1) And ethylene glycol (EG, gamma. 48.2mN m^-1) Only a partial bounce is possible with a small fraction of EG attached to the coating. In contrast, N-dimethylformamide (DMF, γ ═ 34mN m^-1) It is possible to completely bounce on a coating with multilevel micro/nanostructures (e in fig. 1). In addition, 15nm SiO was investigated₂The effect of mass ratio on super amphiphobic performance (figure 16). It was found by studying the present application that when the suspension contains 40 wt% SiO₂(15nm) the composite coating has perfect lyophobic performance.

FAS grafted SiO with high degree of fluorination₂And a multi-layer micro/nano composite structure of poly HFBA to make the coating have lower surface energy, wherein the fluorinated SiO₂The multi-stage micro-nano structure material of (-15 nm +500nm) and α -cellulose is lower than other two coatings, and the surface energy is about 12.98mN m^-1(FIG. 17, Table 1). Nanoscale SiO₂The combination of (15nm and 500nm) and micron-sized cellulose plays a crucial role in reducing the whole solid-liquid contact area and capturing larger air cushion, the solid-liquid interface is converted into a solid-gas interface as much as possible to form a relatively stable air layer, and a Cassie-Baxter model is formed to prevent liquid drops from penetrating. The coating can also be sprayed on different substrates (e.g. iron sheet, ceramic tile, wood and cotton fabric) and completely repel different liquids (including yogurt, coffee, octane and water) (g in fig. 1). The versatility of the coating is attributed to the special adhesion properties of the poly HFBA.

Elastography of organic liquids

The bouncing of droplets on a super-amphiphobic surface is an important indicator for assessing the liquid repellency of a coating. To date, water droplets have been reportedThe bouncing behavior on superhydrophobic surfaces, but very few studies have been made on the bouncing behavior of organic droplets on superamphiphobic coatings, and the application here explores the bouncing behavior of organic droplets. Under a higher Weber number, the liquid drop can be broken when impacting the super-amphiphobic surface, which is mainly because of the competitive relationship between the internal energy of the liquid drop and the surface tension of the liquid, when the dynamic balance of the internal energy of the liquid drop and the surface tension of the liquid is broken, the liquid drop is split into broken liquid, so that the mass of the liquid drop before and after breaking is not conservative, and the energy conversion of the liquid drop bouncing process cannot be explored. For example, upon release of a DMSO droplet at 15cm, the droplet may break. Corresponding impact velocity of 1.71m s^-1(We ═ 88.4), it is therefore of practical interest to determine the maximum weber number of the liquid, i.e. the maximum release height of a volume of droplets. As shown in a of FIG. 2, the maximum height of the free fall of droplets of n-hexadecane, toluene, chlorobenzene, DMF, DMSO, EG, diiodomethane, water, etc. at a certain height was investigated. For example, EG droplets have a maximum rupture height of 37cm, which means that EG droplets can still maintain integrity and bounce when released at a height of 36cm, We 188.7. The maximum breaking height of the liquid has guiding significance to engineering practice. In the work of this application, all liquid is released below the break-up height (maximum release height) to ensure droplet integrity.

FIG. 2 (a) maximum break-up height of different droplets with a volume of 6. mu.L. (b) Taking n-hexadecane as an example, the whole bouncing process of the liquid drop is adopted, and the yellow area corresponds to the first bouncing process. (c) The contact time of the water and organic liquid released at different heights. The water has the same contact time with the solid surface at different release heights, and the organic liquid has different contact times with the solid surface at different release heights. (d) A photograph of the first bounce process of n-hexadecane. The contact time includes the spreading time (t)_s) And retraction time (t)_r). Maximum spreading diameter (Dmax) at which the droplet spreads to the maximum spreading diameter. The droplets are expressed as v₁Is in contact with the surface at a velocity of v₁The velocity of' is away from the surface. The velocity of the second impact surface is upsilon₂。

By passingThe bounce process of the organic droplets was explored by a high speed camera with a frame number of 7400fps, taking n-hexadecane as an example, and the first contact process is shown as d in fig. 2, corresponding to the yellow region in b in fig. 2. A 6 μ L droplet (R ═ 1.2mm) was released from a height of 6 cm. At the instant of contact with the surface, when t is 0, the velocity of the droplet is defined as v₁＝1.08ms^-1. The droplet starts to spread and reaches the maximum spread diameter (Dmax) when t is 2.4 ms. Then, the drop is measured at t ═ 13.8ms and v₁The speed of' retracts and leaves the surface. Contact time (t)_c) Is called spreading time (t)_s) And retraction time (t)_r) The sum of tc ═ 13.8ms for n-hexadecane. After the second impact process, the rebounding drop will be at v₂＝0.32m s^-1Is caused to strike the surface. When a drop of n-hexadecane can bounce 6 times on the super-amphiphobic coating for 251.2ms, it shows that the coating has excellent repulsion to n-hexadecane (b in fig. 2). The contact time of the liquid on the solid surface can be an important indicator of the ability of the coating to repel liquid. In this work, the contact time was only the spreading and retraction time when the first droplet was in contact with the super-amphiphobic substrate. It has previously been demonstrated that the contact time of water droplets is independent of the impact velocity over a wide range of weber numbers. Similar results were obtained in the work of the present application, where the contact time of the water droplet was about 10.2ms, and was independent of the height of release. However, the contact time of the organic liquid depends on the volume of the droplets and the intrinsic properties of the organic solvent (e.g. viscosity, surface tension and density) and the impact velocity. When controlling a volume of organic droplets (e.g., 6 μ L), the contact time will vary depending on the type of organic liquid. For any organic liquid, the higher the release height, the longer the contact time (c in fig. 2).

Furthermore, the relationship between contact time and the intrinsic properties of the organic liquid (e.g. density, viscosity and surface tension) was investigated. In order to make the measured contact time as accurate as possible, ten contact times were measured and averaged at different locations on the same super-amphiphobic surface. As shown in fig. 3 a (table 2), three groups of liquids with the same volume (6 μ L) and different surface tensions were released at the same height (6 cm). Each group of liquids with similar viscosities has similar contact times. For example, the contact times of o-dichlorobenzene and pyridine having similar viscosities of 0.9 mPas were about 14.50 and 14.42ms, respectively, indicating that the effect of surface tension on contact time was not significant. Similarly, the results of releasing three sets of liquids with similar surface tensions and different viscosities, as shown in fig. 18 (table 3), indicate that the contact time increases with increasing viscosity. Thus, during the energy dissipation phase, viscous forces are the main factors affecting the contact time. Therefore, a number of organic liquids were selected to explore the effect of viscosity on contact time (fig. 19b and table 4). It was found that two regions with a viscosity below 2mPa s and above 2mPa s were obtained. In each zone, the contact time gradually increases with increasing viscosity (b in fig. 3). It is difficult to understand the jump of the contact time in the vicinity of the viscosity of 2 mPas, which requires intensive studies. In addition, the effect of the weber number (or impact velocity) on contact time was also investigated. As shown in fig. 3c, three liquids (EG, tetrabromoethane, diiodomethane) with different viscosities are released at different heights (determine weber number or impact velocity). The contact time of the three droplets increases with increasing weber number (or impact velocity). The higher the weber number, the more pronounced the effect of viscosity on contact time (c in fig. 3). However, at very low weber numbers, the difference in contact time of the three droplets is not significant.

FIG. 3 (a) contact times for three groups of liquids with similar viscosities and different surface tensions. (b) Effect of liquid viscosity on contact time. (c) Contact time of different liquids at different weber numbers. (d) Contact time and number of bounces of high viscosity glycerol with viscosity from 25.6 to 154mPa s at different temperatures. (e) Photograph of the bouncing process of a glycerol droplet with a viscosity of 297.8mPas at 40 ℃. The time interval is 8 mm.

Bouncing of a liquid on a solid surface is a very complex process. To understand the relationship between contact time and droplet properties, theoretical analysis was performed. When the drop falls freely at a certain height, it has kinetic energy (E) at the instant of contact with the superamphiphobic surface_ko) And has a surface energy (E)_sa) After impact, kinetic energy is used for the deformation of the liquid dropletsOvercoming the loss of viscosity. When t is ts, the droplet diameter reaches Dmax. In this state, the kinetic energy is zero and the total energy is the surface energy (E)_sb). During retraction, the surface energy is further consumed by viscous losses. Because of the lower surface energy of the super-amphiphobic surface, frictional losses during impact are negligible. The viscous dissipation (E μ) during spreading and shrinking was determined as the following relationship:

v represents the volume of the drop, assuming that the drop can be considered to be cylindrical at Dmax, i.e., the drop is cylindrical in shape

h is the thickness of the cylinder. Equation (1) becomes:

the viscous energy dissipation (E μ) relationship accounts for the impact velocity and viscosity of the liquid on drop bounce. The viscous effect is more pronounced with increasing impact velocity. Thus, viscosity results in higher viscous energy loss at higher impact velocities, resulting in longer contact times, consistent with the experimental results of the present application (fig. 3).

In practical applications, the microstructure of the coating can be destroyed by the viscous liquid during contact, thereby affecting performance. Therefore, repellency to high viscosity liquids is also an important criterion for evaluating coating performance. In the case of viscous liquid glycerol (table 5), the contact time gradually increased with increasing viscosity. Accordingly, as the viscosity of glycerin was changed from 25.6mPa s to 154mPa s, the number of bounces of the liquid was reduced from 7 to 3 (d in fig. 3). This is because a high viscosity liquid will cause excessive energy consumption of the droplets when contacting a solid surface. Even with glycerol having a viscosity of 297.8mPa s at 40 ℃, the droplets rebound 3 times at a release height of 6cm (e in fig. 3), indicating that the coating of the present application has excellent properties against high viscosity liquids.

Mechanical stability

The mechanical strength of the super-amphiphobic coating is very important in practical applications. Three different types of mechanical strength tests were performed on the coatings, including high pressure fluid impact, abrasion and peel tests (fig. 4). At a distance of 15cm from the coated glass plate, the water stream impinges on the super-amphiphobic coating (a in fig. 4). The durability of the coating to water spray depends on the water pressure and spray time. At a water pressure of 400kPa, the impact velocity of the water is about 27.8m s-1, corresponding to a heavy rain landing velocity (8-9 ms)^-1) Three times higher than the reported water impact velocity used to evaluate the mechanical durability of the super-amphiphobic coating (1.4m/s) by more than 20 times. The performance of the coatings was tested on a cycle of 2 minutes with n-hexadecane bounce as a standard. When the water impact lasts for four minutes, n-hexadecane can bounce seven times. The number of n-hexadecane bounces slightly decreased with increasing impact time (b in fig. 4). After 14 minutes of impact, the n-hexadecane still bounced five times with little change in the surface morphology of the coating (c in fig. 4), reflecting the good fluid impact resistance of the coating. Notably, the coatings of the present application can also withstand the impact of hot fluids. Typically, a super-amphiphobic surface has a high repulsive force to room temperature liquids, but the ability to repel hot liquids is greatly reduced. This is because the lower surface tension of the hot fluid makes it a better "wetting agent" into the pores of the rough surface. In the coatings of the present application, the CA and SA of water, diiodomethane and n-hexadecane were measured at different temperatures after the coating had been impinged with water for 14 minutes. As shown by d in fig. 4, the CAs of all liquids is above 155 ° and the SAs is slightly increased but still less than 10 ° at temperatures between 25 and 80 ℃, indicating a good repulsion of the coating against the hot fluid.

As a second mechanical robustness test, the abrasion resistance of the coating was measured using a 100g weight and 1500cw sandpaper (fig. 19) and a 5cm movement of the coating on the sandpaper was defined as a friction cycle, after 30 cycles the CA of n-hexadecane was still higher than 160 ° (e in fig. 4). The SEM images also showed no change in the surface morphology of the coating after 30 rubbing cycles (fig. 19). The third mechanical test is an adhesion measurement, which is tested by peeling with a strong adhesive tape. When the coating suspension was sprayed onto cotton fabric, the CA of n-hexadecane was above 160 ° after 30 stripping cycles, although the structure of the coating was slightly changed, and the drops could bounce 6 times (f in fig. 4). Fig. 20) indicating excellent adhesion strength of the coating to the substrate.

Chemical stability

In addition to having good mechanical properties, the coatings of the present application can withstand harsh environments, such as highly corrosive environments, high/low temperature environments, and Ultraviolet (UV) light. Aqua regia (a high concentration of high concentration hydrochloric acid (HCl) and nitric acid (HNO)₃) In a volume ratio of 3: 1) was used to evaluate the chemical resistance. Although this extreme chemical attack is not very common in practice, it is a meaningful way to measure the chemical stability of the coating. The coated glass was immersed in a beaker of aqua regia and removed every 20-30 minutes. After rinsing with water and drying, CA and contact time were measured. As shown in fig. 5 a, the CA of the original coating to n-hexadecane was 169 ° and the contact time was 14.2 ms. After 60 minutes of soaking in aqua regia, the CA of n-hexadecane was still 155 °, and the contact time increased to 15.2 ms. SEM images showed no significant damage to the coating after 60 minutes immersion (b in figure 5). This may be due to the following reasons: fluorocarbon chains tend to extend beyond the surface due to the lower surface energy. C-F (485KJ mol)^-1) Bond energy ratio of (1) C-H (411KJ mol)^-1) Is much larger, so that the coating is particularly stable and even resistant to aqua regia corrosion. Next, the coating of the present application will be used in extreme temperature environments. CA and SA of n-hexadecane were about 168 ° and less than 5 °, respectively, at 20 ℃. The sample is left at-25 ℃ for 48 hours and then at high temperature for 6 hours, optionallyIt was found that the CA and SA values hardly changed after the low and high temperature treatment (c in FIG. 5). The structure of the coating did not change after the high temperature treatment at 220 ℃, indicating that the coating had very high thermal stability (d in fig. 5). In addition, CA and SA of n-hexadecane hardly changed when the coated glass plate was irradiated with uv rays at 245nm for 24 hours, indicating that the super-amphiphobic coating had excellent uv resistance (fig. 21).

Discussion of the related Art

In summary, the present application is based on SiO of different sizes₂And cellulose, and excellent adhesion properties over other coatings reported in the literature, and has excellent mechanical and chemical stability and a combination of significant large-scale manufacturability advantages in raw materials and manufacturing processes. The super-amphiphobic coating has wide application in surface/interface regions and has special wettability. Thus, a simple case of applying the coating is further proposed.

In the first example, super-amphiphobicity enables ships and certain equipment to float and work on oil. Here, the effect of the super-amphiphobic coating on buoyancy stability and load-bearing capacity was studied by using a mini-boat model. In fig. 6 a shows the original boat (left) and the coated boat of the super-amphiphobic coating (right). The original boat had a depth of infiltration of approximately 8mm above the water surface. After spraying, the depth of wetting on the water and peanut oil was 4mm and 6mm respectively (b in FIG. 6). The depth of immersion in water is significantly reduced to 50% of the depth of immersion of the original vessel. The depth of wetting in water and oil is different for the following reasons: the density and surface tension of peanut oil is less than that of water, which results in higher buoyancy of the water. When the original vessel carries a weight of 100g, the vessel will slowly sink to the bottom (c in fig. 6, upwards). However, when the load of the ship coated with the super-amphiphobic coating is 360g, the ship can still float on the water surface (c in fig. 6, downwards). Clearly, the super-amphiphobic coating changes the buoyancy and load bearing capacity of the ship. After painting, the maximum load becomes 6 times of the original ship (d in fig. 6), which is of great significance for increasing the cargo capacity of the cargo ship. The stability of the ship in oil and seawater environments was also investigated. For the original vessel, the depth of immersion increased gradually over time at a load of 100 g. After 6 hours, the original vessel sinks to the sea and the oil bottom (fig. 22). In contrast, the coated boat was stable floating in seawater and peanut oil for 72 hours under a load of 100g, without significant change in the depth of immersion (e in fig. 6). This shows that the super-amphiphobic coating not only can greatly increase the load of the ship, but also has good stability.

In a second example, surface icing is a major problem in cold regions, particularly for the aeronautical, maritime or maritime industries. Coatings with multi-level micro/nano structures can minimize localized liquid-solid contact due to the presence of the air layer, thereby reducing heat transfer at the liquid-solid interface. In view of this, the present application explores the effect of ultraamphiphobicity on water freezing rate and facilitates the use of specific wetting coatings for freeze protection. The water droplet was placed on the pre-cooled coated substrate and held at-25 c as shown in fig. 6 f. The ice formation time on the coated iron, tile, glass and fabric was changed from 2.5, 3, 5 minutes to 9, 12, 13, 28 minutes, respectively (f in fig. 6, fig. S23). The different freezing times are due to the four matrices (iron flakes: 55w m)^-1k^-1And (3) ceramic tile: 1.5w m^-1k^-1Glass: 0.7w m^-1k^-1The fabric: 0.2w m^-1k^-1) Is used. The super-amphiphobic coating can obviously delay the freezing time and provides an application prospect for the anti-icing field.

On the other hand, the adhesion of the super-amphiphobic coating greatly limits the practical application of the super-amphiphobic coating. In order to increase the adhesion of the coating, an external crosslinking agent is generally selected to chemically crosslink the fluoropolymer and the substrate, thereby increasing the adhesion of the coating. For general coating, the silane coupling agent is a common hybrid cross-linking agent, has high reactivity, contains a plurality of cross-linked functional groups, can perform self-crosslinking while cross-linking a substrate, and can select silane coupling agents with different functional group side chains according to practical application. Particularly, after the silane coupling agent is subjected to crosslinking reaction, a very firm Si-O-Si crosslinking network can be formed, because of the unique organic-inorganic hybrid chemical structure of the silicon-oxygen bond, the polysiloxane and inorganic or organic materials have excellent adhesive performance, the hydrophobic performance of the coating is improved while hydrophilic groups are not introduced, and the silicon-oxygen-silicon crosslinking agent is a preferable choice in the crosslinking agent. Based on this, in this system, the present application first tried the commercialized KH900 and KH570 silane coupling agents, spray the prepared super-amphiphobic suspension on a glass substrate, and the adhesion test was performed with a 1500CW sandpaper loaded with 100g weight, and as a result, as shown in fig. 10, the present application found that the adhesion of the coating is particularly affected by the addition of different proportions of the adhesive, and for these two silane coupling agents, when 7.5 wt% was added, the adhesion of the coating was the best, the adhesion of KH900 to the substrate was better than that of KH570, and it can be seen that when KH570 was used as the adhesive, a large amount of coating was peeled off on the sandpaper, so the present application selected KH900 as the adhesive and analyzed the coating performance by means of contact angle, and found that when KH900 was used as the adhesive, the coating possessed good adhesion and super-hydrophobic performance, but for drops of low surface tension such as n-hexadecane, the effect of super-amphiphobic is not achieved, which is not in accordance with the purpose of the present application. However, the acrylate polymer can be copolymerized with a plurality of vinyl monomers to improve the physical properties of the polymer, and more importantly, ester groups and hydrogen bonds have stronger binding capacity, so the acrylate polymer has wider application as an adhesive. Considering that the adhesion of the coating can be enhanced while oleophilic groups are not introduced, hexafluorobutyl acrylate (HFBA) is selected as the adhesive, and the performance of the adhesive is explored. The amount of fluoromonomer used, particularly the order of addition and the use of initiators, while providing adhesion, plays a critical role in the final properties of the coating. Firstly, when the influence of the initiator on the coating performance is verified, when the initiator is added, the prepared super-amphiphobic suspension is sprayed on a glass slide, after drying, a uniform compact super-amphiphobic coating cannot be formed, and after the suspension with the surface in a chap shape (figure 11) and without the initiator is sprayed and dried, a uniform coating can be formed. OH "is a nucleophile that can polymerize C ═ C radicals in the system, and the effect of adding an initiator is very different from the effect of not adding an initiator, so this application chooses not to use an initiator. In the same manner as the method for verifying the performance of the silane coupling agent in the reaction system, almost no coating was peeled off from the sandpaper at the time of addition of 6.5 wt%, and the adhesion of the coating was optimized. The performance of the coating is further optimized while ensuring adhesion. The influence of the addition sequence on the performance of the coating is researched, when various monomers are added for the third time, the addition sequence of the adhesive has great influence on the performance of the coating, the performance of the coating is detected by utilizing a contact angle, when HFBA is added firstly and then TEOS and FAS are added, the contact angle of n-hexadecane is 120 degrees, when HFBA is added finally, the contact angle of n-hexadecane is 168 degrees, and the super-amphiphobic coating with better adhesive force is achieved.

Mixing 10mL of anhydrous ethanol and 3mL of ammonia water, adding 0.5mL of HFBA, sampling 10 μ L every 15 minutes, observing 1730cm^-1Change of C ═ C peak. It can be seen that 1730cm over time^-1The peak at (A) gradually disappeared, demonstrating that OH-can be used as a nucleophile to attack the double bond.

The nature of wetting refers to the adhesion of a liquid to a solid surface, whereas the adhesion (W)_a) Related to the change in free energy of the system.

The definition of work of adhesion is expressed as:

W_a＝γ_SV+γ_LV-γ_SL(1)

the relationship between surface energy and interfacial energy can be described by the young's equation:

wherein, γ_SV，γ_SLAnd gamma_LVSolid-gas, solid-liquid and liquid-gas interfacial energies, respectively; θ is the contact angle of the liquid on the three-phase contact line on a smooth surface.

Table 1 contact angle data and calculated surface free energy for three coatings

Table 2 the effect of surface tension on contact time was explored by selecting three groups of similar droplets with different surface tensions and viscosities

Figure 18 by selecting the effect on contact time of three groups of droplets having similar surface tension but different viscosities, it can be seen that the contact time increases progressively with increasing viscosity.

Table 3 the effect of viscosity on contact time was explored by selecting three groups of droplets with similar surface tension.

TABLE 4 contact time of droplets of different properties

Table 5 bounce dynamics of viscous glycerin at different temperatures. By temperature control, glycerol droplets of different viscosities can be obtained.

Fig. 19 (a) is a schematic diagram of a wear test. SEM images at low (b) and high (c) magnification of the coating after 30 wear cycles.

Fig. 20 (a) is a schematic diagram of a peeling cycle test. Low (b) and high (c) magnified SEM images of the coating after 30 peel cycles.

FIG. 21 shows irradiation of n-hexadecane with CA and SA at different times.

Figure 22 a blank boat of 100 gram load floating on water and peanut oil.

It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention is not limited thereto, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications and equivalents can be made in the technical solutions described in the foregoing embodiments, or equivalents thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention. Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims

1. A preparation method of a super-amphiphobic coating is characterized by comprising the following steps:

mixing SiO₂Dispersing the nano-particles and α -cellulose in ethanol/ammonia water solution, then adding tetraethyl silicate and 1H, 1H, 2H, 2H-perfluorodecyl trimethoxy silane dropwise in sequence for hydrolysis, and adding the mixture into SiO₂Nanoparticle and α -cellulose coated with SiO₂；

Reacting tetraethyl silicate and 1H, 1H, 2H, 2H-perfluorodecyl trimethoxy silane in a solvent system to generate polysiloxane and form suspension;

2. The method of preparing a super-amphiphobic coating of claim 1, wherein the SiO is₂The mass ratio of the nanoparticles to the α -cellulose is 2: 3-5.

3. The method of preparing a super-amphiphobic coating of claim 1, wherein in the suspension, SiO is present₂The concentration of (A) is 30-50 wt%.

4. The method of preparing the super-amphiphobic coating of claim 1, wherein the volume ratio of tetraethyl silicate, 1H, 2H-perfluorodecyltrimethoxysilane to hexafluorobutyl acrylate is 2-3: 1-1.5: 2.

5. the method of preparing a super-amphiphobic coating according to claim 1, wherein the coating conditions are: mechanically mixing the mixture in a water bath at the temperature of 50-55 ℃ for 6-8 h;

or the polysiloxane is generated by mechanically mixing for 5-10 min in a water bath at 50-55 ℃.

6. The method of preparing a super-amphiphobic coating of claim 1, wherein the conditions of the self-polymerization reaction are: mechanically mixing for 1.5-3 h at 50-55 ℃.

7. The method of claim 1, wherein the spraying comprises spraying 2-3 mL of the suspension onto the surface of a horizontally disposed substrate from a vertical distance of 10-12 cm using a spray gun.

8. The method for preparing the super-amphiphobic coating according to claim 1, wherein after the spraying is finished, the super-amphiphobic coating is dried at 75-90 ℃ for 5-8 hours.

9. A super-amphiphobic coating prepared by the method of any of claims 1-8.

10. Use of the super-amphiphobic coating of claim 9 in the field of droplet manipulation, self-cleaning, heat transfer, anti-icing or liquid-liquid separation.