CN115991947A - Layered bridging cross-linked heterostructure flexible nano coating and preparation method and application thereof - Google Patents
Layered bridging cross-linked heterostructure flexible nano coating and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a kind of nanometer coating, disclose a lamellar bridging cross-linking heterostructure flexible nanometer coating and its preparation method and application, it synthesizes the organic thermoelectric nanowire at first, modify the viscous organic macromolecule on its surface to get the viscous organic thermoelectric nanowire through cross-linking agent, then mix and disperse in solvent with the lamellar conductive nanometer material to make into the mixed coating, then coat on flammable substrate to get final product, the coating prepared in this invention has sensitive, accurate and repeatable temperature sensing function, can monitor the heating stage before the conflagration happens effectively, and can respond and send the early warning signal rapidly at the high temperature or burning; meanwhile, the flame retardant coating has excellent flame retardant property, good adhesiveness and flexibility, can be applied to various inflammable base materials by convenient methods such as casting, brushing, spraying and dipping, and has wide application prospect in the fields with high requirements on fire safety such as electronics, electricity, transportation, building decoration and the like.
Description
Technical Field
The invention relates to a nano coating, in particular to a layered bridging cross-linked heterostructure flexible nano coating, and a preparation method and application thereof.
Background
In recent years, with the wide application of polymer materials in various fields, fire accidents caused by the combustion of polymer materials are more and more frequent, especially in the field of electrical equipment. For example, 2021, 1-10 months, electrical fire accidents account for up to 50.4% of all fire accidents in china. This is due on the one hand to the high flammability of the polymer material and on the other hand to the frequent occurrence of faults in the electrical equipment such as short circuits, overloads, etc. In addition, flexible electronic materials have been rapidly developed in recent years, but the frequency of electrical failure is further exacerbated by their complex structure and frequent deformation during application. Therefore, the flame retardant property of the high polymer material is improved, and the temperature of the high-incidence area of the electrical failure is monitored, so that the flame retardant material has important significance for reducing the occurrence of the electrical fire accident.
The preparation of nano-flame retardant coatings with temperature sensing capabilities is considered to be one of the most effective methods to achieve the above-mentioned objectives. Among them, graphene Oxide (GO) nanocoating has been attracting attention because of its layered ordered structure and thermal resistance effect, and excellent flame retardant properties and sensitive temperature sensing function. However, the thermal resistance effect of GO comes from its thermal reduction, leading to its temperature sensing function with the following drawbacks: (1) The thermal reduction rate is temperature dependent, resulting in temperature sensing insensitivity at lower temperatures (< 250 ℃); (2) The thermal reduction reaction is irreversible, so that the temperature sensing function is not repeatable; (3) Converting the resistive signal to an electrical signal that triggers a fire alarm requires auxiliary equipment such as a power supply, which adds to the complexity and instability of the temperature sensing system. These drawbacks severely limit the practical application of GO nanocoating in the field of fire alarm. Therefore, there is an urgent need to develop new temperature sensing systems.
Thermoelectric materials are one of the most promising materials for temperature sensing. Because carriers in the thermoelectric material can migrate along the temperature gradient, a voltage signal is generated between high and low temperature regions, and the voltage signal strength is proportional to the temperature difference, and good regularity and repeatability are shown. Among thermoelectric materials, inorganic thermoelectric materials have high thermoelectric efficiency, but their flexibility and adhesiveness are poor, and their application in flexible electronic devices is severely limited. Meanwhile, the inorganic thermoelectric material hardly has any flame retardant effect. In contrast, organic thermoelectric materials have good flexibility, adhesion, and char formation capability, and are uniquely advantageous when applied to the field of flexible electronic devices. However, the thermoelectric efficiency of organic thermoelectric materials is generally much lower than that of inorganic thermoelectric materials, which directly affects the sensitivity and stability of voltage signals. Therefore, it is urgent to improve the thermoelectric efficiency of the organic thermoelectric system.
Disclosure of Invention
Aiming at the problem of low thermoelectric efficiency of an organic thermoelectric material in the prior art, the invention provides a layered bridging cross-linked heterostructure flexible nano coating, and a preparation method and application thereof.
In order to solve the technical problems, the invention is solved by the following technical scheme:
the preparation method of the layered bridging cross-linked heterostructure flexible nano coating comprises the following steps:
step (1) of preparing an organic thermoelectric nanowire dispersion, comprising the following steps:
step S11, adding a surfactant, an organic thermoelectric monomer and dopamine into a solvent A with the pH value of 1-5 to obtain a mixed solution A;
preferably, the pH of the solvent A in the step is obtained by adding a pH regulator to the solvent A, wherein the pH regulator is one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and p-toluenesulfonic acid;
in addition, adding the surfactant, stirring for 3-24 hours, fully dissolving the surfactant, adding the organic thermoelectric monomer and the dopamine, and continuing stirring for 1-6 hours;
step S12, dropwise adding an oxidant solution into the mixed solution A for a mixed reaction for 6-24 hours to obtain a mixed reaction solution A;
preferably, the oxidant solution in the step is prepared by dissolving an oxidant in another solvent A, wherein the temperature of the mixed reaction solution A in the dripping process is-5-80 ℃, the mixed reaction solution A is slowly dripped within 15-60min, and the mixed reaction solution A is stirred for 6-24h after dripping.
Step S13, centrifuging the mixed reaction solution A, washing the precipitate and uniformly dispersing the precipitate in the solvent B for standby, thus obtaining an organic thermoelectric nanowire dispersion liquid;
step (2) preparing viscous organic thermoelectric nanowires, comprising the following steps:
s21, adding a viscous organic polymer solution into the organic thermoelectric nanowire dispersion liquid obtained in the step (1), and stirring for 10-60min to fully disperse the organic thermoelectric nanowire dispersion liquid;
s22, adding a catalyst, adjusting the reaction temperature to 40-120 ℃, and dripping a cross-linking agent solution into the mixture within 15-60min for cross-linking reaction for 4-24h to obtain a mixed reaction solution B;
step S23, centrifuging the mixed reaction liquid B, washing the precipitate and uniformly dispersing the precipitate in a solvent C for standby, thus obtaining viscous organic thermoelectric nanowire dispersion liquid;
step (3) preparing a layered bridging cross-linked heterostructure flexible nano-coating, which comprises the following steps:
step S31, dispersing the layered conductive nano material in a solvent C to prepare layered conductive nano material dispersion;
step S32, uniformly mixing the layered conductive nano material dispersion liquid with the viscous organic thermoelectric nano wire dispersion liquid obtained in the step (2) to obtain a mixed dispersion liquid;
and step S33, coating the mixed dispersion liquid on a flammable substrate, and drying to obtain the layered bridging cross-linked heterostructure flexible nano coating.
Preferably, the drying in this step is carried out by placing in a forced air oven and drying at 30-100deg.C for 0.1-12 hr.
Preferably, the solvent A, the solvent B and the solvent C are one or more of deionized water, ethanol, acetonitrile, acetone, N-dimethylformamide, tetrahydrofuran, N-butanol and N-hexane.
Preferably, the organic thermoelectric monomer in the step (1) is one or more of pyrrole, aniline, 3, 4-ethylenedioxythiophene and carbazole;
the surfactant is one or more of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, cetyltrimethylammonium bromide, sodium fatty alcohol polyoxyethylene ether sulfate and polyvinylpyrrolidone;
the oxidant solution is obtained by dissolving an oxidant in a solvent, wherein the oxidant is one or more of vanadium pentoxide, potassium dichromate, ferric chloride, ammonium persulfate, ferric nitrate, methyl triphenylphosphine persulfate and ferric p-toluenesulfonate.
Preferably, the viscous organic polymer in the step (2) is one or more of polyvinyl alcohol, sodium alginate, cellulose acetate, carboxymethyl chitosan, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose;
the catalyst is one or more of sodium hypophosphite, sodium hydroxide and potassium hydroxide;
the cross-linking agent is one or more of glyoxal, glutaraldehyde, glyoxal, butane tetracarboxylic acid and epichlorohydrin.
Preferably, the layered conductive nanomaterial in step (3) is one or more of graphene nanoplatelets, graphene nanoribbons, and MXene nanoplatelets.
Preferably, in the step (1), the mass ratio of the surfactant to the organic thermoelectric monomer is 0.5:1-2:1, the mass ratio of the dopamine to the organic thermoelectric monomer is 0.5:1-2:1, and the mass ratio of the oxidant to the organic thermoelectric monomer is 2:1-8:1;
in the step (2), the mass ratio of the viscous organic polymer to the organic thermoelectric nano wire is 0.3:1-1.2:1, the mass ratio of the catalyst to the crosslinking agent is 1:1-3:1, and the mass ratio of the crosslinking agent to the viscous organic polymer is 0.05:1-0.4:1;
in the step (3), the mass ratio of the layered conductive nano material to the viscous organic thermoelectric nano wire in the mixed dispersion liquid is 0.25:1-4:1.
Preferably, the mixed dispersion of step (3) is applied to the flammable substrate 1 to 24 times with one or more of spraying, brushing and dipping, each spraying or brushing having an application rate of 0.05 to 0.20mL/cm 2 The soaking time period for each dip-coating is 0.5-10min.
Preferably, the mixed dispersion in step (3) is homogeneously mixed by one or both of stirring and ultrasonic treatment for 15 to 240 minutes.
The layered bridging cross-linked heterostructure flexible nano coating is prepared by the preparation method of the layered bridging cross-linked heterostructure flexible nano coating.
Preferably, the thickness of the coating is 5-300 μm.
The application of the layered bridging cross-linked heterostructure flexible nano-coating is applied to flammable and flexible materials such as films, fabrics, polymer foams and the like.
The invention has the remarkable technical effects due to the adoption of the technical scheme:
(1) The invention synthesizes viscous organic thermoelectric nano wires, and disperses the viscous organic thermoelectric nano wires and layered conductive nano materials in a solvent to prepare mixed dispersion liquid, and the layered bridging cross-linked heterostructure flexible nano coating with temperature sensing and flame retarding functions is prepared on various inflammable base materials such as films, fabrics, foaming materials and the like by a convenient method such as brushing, spraying or dipping.
(2) The layered conductive nano materials can be orderly arranged in the process of co-assembly, and the viscous organic thermoelectric nano wires can bridge the layered conductive nano materials together, so that on one hand, an integrated conductive network is constructed, and the conductivity of an organic thermoelectric system is improved; on the other hand, a rich heterogeneous interface is formed, low-energy carriers can be scattered, and the Seebeck coefficient of an organic thermoelectric system is improved. In addition, the layered ordered structure can scatter low-energy carriers and provide a high-speed transmission channel for high-energy carriers. According to the thermoelectric figure of merit formula (zt=s 2 T sigma/k, S is the seebeck coefficient, T is absolute temperature, sigma is electrical conductivity, k is thermal conductivity), and an increase in electrical conductivity and seebeck coefficient directly brings about an increase in thermoelectric efficiency of the organic thermoelectric system, giving it a sensitive, accurate and repeatable temperature sensing function.
(3) The coating provided by the invention has an integrated layered orderly bridging conductive network and rich heterogeneous interfaces, can improve the conductivity of a system, scatter low-energy carriers and provide a high-efficiency transmission channel for high-energy carriers, thereby effectively improving the thermoelectric efficiency of an organic thermoelectric system and enabling the organic thermoelectric system to display a sensitive, accurate and repeatable temperature sensing function. For smaller temperature rise, the coating can output regular voltage signals, so that the temperature rise stage (100-350 ℃) before the fire disaster occurs can be effectively monitored, early warning signals can be quickly responded and sent out at high temperature or in combustion, and fire alarms can be triggered within 1.9s when the fire disaster is contacted. The invention solves the problem that the sensitivity, repeatability, flexibility and flame retardance of the existing fire early-warning system are difficult to be compatible.
(4) The layered conductive nano materials in the coating provided by the invention are orderly arranged, and the adhesive organic hot wire nano wires bridge and crosslink the layered conductive nano materials together to form a compact structure. When the adhesive organic hot wire nanowire is subjected to high temperature, the adhesive organic hot wire nanowire can be efficiently carbonized, and a carbonized product adheres thermally stable layered conductive nano materials together to form a porous carbonized layer with a compact surface, so that excellent heat insulation and oxygen isolation effects are exerted, the mass transfer and heat transfer process of the combustion of a flammable substrate can be effectively blocked, and the flame retardant property of the flammable substrate is remarkably improved.
(5) In the coating provided by the invention, the surfaces of the viscous organic thermoelectric nanowire and the layered conductive nanomaterial both contain rich nitrogen-containing or oxygen-containing polar groups, and the coating has excellent intrinsic flexibility, and the nano coating constructed by co-assembling the viscous organic thermoelectric nanowire and the layered conductive nanomaterial has good flexibility and adhesion. Meanwhile, the preparation process of the coating provided by the invention is simple and easy to control, has low requirements on production equipment, and has wide application prospect in the field of flexible electronic equipment with urgent requirements on fire safety.
Drawings
Fig. 1 is a fourier infrared spectrum (FTIR) plot of the organic thermoelectric nanowires, tacky organic polymers, and tacky organic thermoelectric nanowires of example 1.
Fig. 2 is a Scanning Electron Microscope (SEM) photograph of the organic thermoelectric nanowires of example 1.
Fig. 3 is an SEM photograph of the sticky organic thermoelectric nanowires of example 1.
Fig. 4 is an output voltage curve of the nano-coating prepared in example 1 and comparative example 1 in a fire early warning test.
FIG. 5 is a linear function of the maximum output voltage of the nanocoating prepared in example 1 as a function of heat treatment temperature.
Fig. 6 is a voltage curve of the nano-coating prepared in example 1, which is repeatedly heat-treated at 200 c for 50 times.
Fig. 7 is an SEM photograph of the surface of the nano-coating prepared in example 6 after flame burning.
Fig. 8 is an SEM photograph of a cross section of the nano-coating prepared in example 6 after flame burning.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Example 1
1) Synthesis of organic thermoelectric nanowires: into a 500mL four-necked flask, 200mL of deionized water was added, the pH was adjusted to about 2 by slowly adding sulfuric acid, 0.5g of sodium dodecylbenzenesulfonate was added, and stirring was performed for 3 hours. Thereafter, 0.4g pyrrole and 0.04g dopamine were added and stirring was continued for 2h. Subsequently, the reaction temperature was adjusted to 0 ℃, 2g of ferric nitrate was dissolved in 50mL of deionized water, and added dropwise to the flask over 30 minutes, and the reaction was stirred for 12 hours after the completion of the dropwise addition. After the reaction, the mixed reaction solution was left to stand to room temperature, centrifuged, the precipitate was washed 3 times with deionized water, and then dispersed in deionized water to prepare an organic thermoelectric nanowire dispersion having a concentration of 2 wt%.
Fourier infrared (FTIR) analysis and Scanning Electron Microscope (SEM) testing were performed on the product of step 1), and the results are shown in fig. 1 and 2, respectively. From fig. 1, it can be observed that the appearance of c=c-N (1674 cm) -1 ) Aromatic c=c (1674 cm) -1 ) and-NH- (1297 cm) -1 ) Is characterized by the presence of obvious-OH (3687-3052 cm) -1 ) Is characterized by an absorption peak. As can be seen from fig. 2, the product of step 1) exhibits a uniform linear structure. The test results show that the organic thermoelectric nano-wire is successfully synthesized.
2) Synthesis of viscous organic thermoelectric nanowires: into a 500mL four-necked flask, 20g of the organic thermoelectric nanowire dispersion with a concentration of 2wt% was added, and the mixture was diluted to 100mL with deionized water. Then, 20g of a polyvinyl alcohol aqueous solution having a concentration of 2wt% was added thereto, and the mixture was stirred for 30 minutes to sufficiently disperse the mixture. Subsequently, 0.3g of potassium hydroxide was added as a catalyst, the reaction temperature was adjusted to 60℃and 7.5g of 2wt% glutaraldehyde aqueous solution was slowly added dropwise over 30 minutes, and the reaction was stirred for 8 hours after completion of the dropwise addition. After the reaction is finished, the mixed reaction solution is stood to room temperature, centrifuged, the precipitate is washed for 3 times by deionized water, and then dispersed in the deionized water to prepare viscous organic thermoelectric nanowire dispersion liquid with the concentration of 2 wt%.
FTIR analysis and SEM testing were performed on the product of step 2), and the results are shown in fig. 1 and 3, respectively. As can be seen from FIG. 1, the presence of-OH (3687-3052 cm) on the infrared spectrum -1 )、C＝C-N(1674cm -1 ) Aromatic c=c (1674 cm) -1 )、-COO - (1408cm -1 )、-NH-(1297cm -1 ) And C-O-C (1112 cm) -1 ) Is characterized by an absorption peak. It can be seen from fig. 3 that the product of step 2) also exhibits a uniform linear structure, but the nanowire diameter is significantly thicker and the surface is rougher compared to the organic thermoelectric nanowire (fig. 2). The test result shows that the adhesive organic polymer is successfully attached and crosslinked on the surface of the organic thermoelectric nanowire, and the adhesive organic thermoelectric nanowire is successfully synthesized.
3) Preparation of a layered bridging cross-linked heterostructure nano-coating with temperature sensing and flame retarding functions: dispersing MXene nano-sheets in deionized water to prepare a layered conductive nano-material dispersion with the concentration of 2wt%, mixing the layered conductive nano-material dispersion with the viscous organic thermoelectric nano-wire dispersion prepared in the step 2) in a ratio of 1:1, adding deionized water, and uniformly mixing the layered conductive nano-material dispersion with the total concentration of 1wt% under the combined action of mechanical stirring and ultrasonic treatment for 30 min. Horizontally placing the polyester film, spraying a layer of mixed dispersion liquid on the surface of the polyester film, wherein the coating amount is 0.12mL/cm 2 Drying in a forced air oven at 50deg.C for 15min. The spraying and drying process was carried out 8 times to give a coating thickness of 65 μm. And (3) completely immersing the cotton fabric and the polyurethane foam material into the mixed dispersion liquid, taking out the mixed dispersion liquid after immersing for 1min, throwing away the redundant mixed dispersion liquid, and putting the mixed dispersion liquid into a blast oven to dry for 1.5h at 80 ℃. The dip-coating and drying process was carried out 2 times to give a coating thickness of 7 μm.
The coated polyester film, cotton fabric and polyurethane foam were subjected to temperature sensing and vertical burning test, and the results are shown in tables 1 and 2.
Example 2
This embodiment differs from embodiment 1 in that: the surfactant in the step 1) is replaced by hexadecyl trimethyl ammonium bromide, the organic thermoelectric monomer is replaced by pyrrole, the stirring time after the organic thermoelectric monomer and dopamine are added is shortened to 1h, the reaction temperature is increased to 50 ℃, the oxidant is replaced by 2g ferric nitrate to 1g ammonium persulfate, and the dripping time of the oxidant solution is shortened to 15min; the viscous organic polymer in the step 2) is replaced by hydroxypropyl cellulose by polyvinyl alcohol, the reaction temperature is reduced to 40 ℃, the crosslinking agent is replaced by epichlorohydrin by glutaraldehyde, and the reaction time after the crosslinking agent solution is dripped is prolonged to 24 hours; the solvent C in the step 2) and the step 3) is replaced by tetrahydrofuran by deionized water; and 3) replacing the layered conductive nano material by the MXene nano sheet into a graphene nano belt. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Example 3
This embodiment differs from embodiment 1 in that: the solvent A in the step 1) is replaced by ethanol by deionized water, the surfactant is replaced by polyvinylpyrrolidone by sodium dodecyl benzene sulfonate, and the stirring time is prolonged to 6 hours after the organic thermoelectric monomer and the dopamine are added; the solvent B in the step 1) and the step 2) is replaced by N, N-dimethylformamide by deionized water; in the step 2), the viscous organic polymer is replaced by cellulose acetate by polyvinyl alcohol, and the catalyst is replaced by sodium hydroxide by potassium hydroxide; the solvent C in the step 2) and the step 3) is replaced by acetone by deionized water; and 3) replacing the middle-layer-shaped conductive nano material by the MXene nano sheet into a graphene nano sheet. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Example 4
This embodiment differs from embodiment 1 in that: the solvent A in the step 1) is replaced by n-butanol, the pH regulator is replaced by p-toluenesulfonic acid by sulfuric acid, the stirring time after adding the surfactant is prolonged to 24 hours, and the oxidant is replaced by ferric nitrate; the solvent B in the step 1) and the step 2) is replaced by acetonitrile by deionized water; the viscous organic polymer in step 2) is replaced by 0.4g of polyvinyl alcohol and 0.48g of methyl cellulose, and the cross-linking agent is replaced by glutaraldehyde. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Example 5
This embodiment differs from embodiment 1 in that: the surfactant in the step 1) is replaced by sodium dodecyl benzene sulfonate, the consumption of dopamine is increased to 0.08g, the oxidant is replaced by 3.2g of methyltriphenyl phosphine persulfate from 2g of ferric nitrate, and the dripping time of the oxidant solution is prolonged to 60min; the solvent B in the step 1) and the step 2) is replaced by N, N-dimethylformamide by deionized water; the viscous organic polymer in the step 2) is replaced by hydroxypropyl methyl cellulose by polyvinyl alcohol, the stirring time after the viscous organic polymer solution is added is prolonged to 60min, the dosage of catalyst potassium hydroxide is reduced to 0.06g, the reaction temperature is increased to 120 ℃, the dosage of cross-linking agent glutaraldehyde is reduced to 0.02g, and the reaction time after the cross-linking agent solution is dripped is shortened to 4h; the solvent C in the step 2) and the step 3) is replaced by normal hexane by deionized water; and 3) replacing the middle-layer-shaped conductive nano material by the MXene nano sheet into a graphene nano sheet. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Example 6
This embodiment differs from embodiment 1 in that: the surfactant in step 1) was replaced with 0.5g sodium dodecyl benzene sulfonate to 0.2g sodium dodecyl sulfate; the catalyst in step 2) is replaced by sodium hypophosphite and the cross-linking agent is replaced by butanetetracarboxylic acid by glutaraldehyde; the concentration of the mixed dispersion in the step 3) is increased to 2wt%, the action time of mechanical stirring and ultrasonic treatment of the mixed dispersion is shortened to 15min, and the coating amount of spraying is increased to 0.2mL/cm 2 The number of spraying and drying was reduced to 4. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Example 7
This embodiment differs from embodiment 1 in that: the organic thermoelectric monomer in the step 1) is replaced by 3, 4-ethylene dioxythiophene by pyrrole, the reaction temperature is increased to 80 ℃, the oxidant is replaced by potassium dichromate by ferric nitrate, and the reaction time after the oxidant solution is dripped is shortened to 6 hours; the viscous organic polymer in the step 2) is replaced by carboxymethyl chitosan by polyvinyl alcohol; and 3) changing the mixing ratio of the middle-layer-shaped conductive nano material dispersion liquid and the viscous organic thermoelectric nano wire dispersion liquid from 1:1 to 4:1, and improving the spraying drying temperature to 100 ℃ and shortening the drying time to 0.1h. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Example 8
This embodiment differs from embodiment 1 in that: the pH regulator in the step 1) is replaced by hydrochloric acid, the pH value is reduced to 1, the surfactant is replaced by sodium dodecyl benzene sulfonate and fatty alcohol polyoxyethylene ether sodium sulfate, the reaction temperature is reduced to-5 ℃, the oxidant is replaced by ferric nitrate and vanadium pentoxide, and the reaction time after the oxidant solution is dripped is prolonged to 24 hours; the viscous organic polymer in the step 2) is replaced by sodium alginate by polyvinyl alcohol, the stirring time after the viscous organic polymer solution is added is shortened to 10min, the dosage of glutaraldehyde as a crosslinking agent is increased to 0.15g, and the dripping time of the crosslinking agent solution is prolonged to 60min; the mixing ratio of the middle-layer-shaped conductive nano material dispersion liquid and the viscous organic thermoelectric nano wire dispersion liquid in the step 3) is changed from 1:1 to 0.25:1. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Example 9
This embodiment differs from embodiment 1 in that: the pH regulator in the step 1) is replaced by phosphoric acid, the pH value is increased to 5, the stirring time after adding the surfactant is prolonged to 12 hours, the organic thermoelectric monomer is replaced by aniline, the consumption of dopamine is reduced to 0.01g, and the oxidant is replaced by ferric nitrate; the viscous organic polymer in the step 2) is replaced by carboxymethyl cellulose by polyvinyl alcohol, the cross-linking agent is replaced by glyoxal, and the dripping time of the cross-linking agent solution is shortened to 15min; the concentration of the mixed dispersion in step 3) was reduced to 0.2wt%, and the amount of sprayed coating was reduced to 0.05mL/cm 2 The number of spraying and drying was increased to 24. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Example 10
This embodiment differs from embodiment 1 in that: the pH regulator in the step 1) is replaced by nitric acid, and the dosage of the surfactant sodium dodecyl benzene sulfonate is increased to 0.8g; the consumption of the viscous organic polymer polyvinyl alcohol in the step 2) is reduced to 0.12g, the consumption of the catalyst potassium hydroxide is reduced to 0.02g, and the consumption of the cross-linking agent glutaraldehyde is reduced to 0.02g; and 3) prolonging the action time of mechanical stirring and ultrasonic treatment of the mixed dispersion liquid to 240min, changing the coating mode of the polyester film from spraying to brushing, prolonging the soaking time of dip coating of the cotton fabric and the polyurethane foam material to 10min, reducing the drying temperature to 40 ℃ after dip coating, and prolonging the drying time to 12h. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Comparative example 1
In order to verify that the layered bridging cross-linked heterostructure nano-coating with temperature sensing and flame retarding functions prepared by the invention can endow the inflammable substrate with the temperature sensing function and improve the flame retarding performance, a polyester film, cotton fabric and polyurethane foaming material which are not coated with the flame retarding coating are used as comparison materials. The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Comparative example 2
In order to verify that the layered bridging cross-linked heterostructure provided by the invention can effectively improve the thermoelectric efficiency of a thermoelectric system and further improve the temperature sensing sensitivity, the viscous organic thermoelectric nano material with irregular synthesized morphology replaces the viscous organic thermoelectric nano wire, and a nano coating is prepared together with the layered conductive nano material for comparison.
The present comparative example differs from example 1 in that: and (3) directly adding the organic thermoelectric monomer and dopamine without adding a surfactant after regulating the pH in the step (1). The results of the temperature sensing and vertical burning tests are shown in tables 1 and 2, and the related test method is the same as example 1.
Test method
1. Fourier infrared spectroscopy (FTIR) analysis: was performed on a Fourier transform infrared spectrometer (Brookfield analysis instruments, model: TENSOR 27). Mixing potassium bromide (KBr) with a sample to be detected in a ratio of 100:1, grinding into fine powder, drying, pressing into slices, enabling infrared interference light to penetrate the slices and collecting absorption spectrum information of the infrared interference light, wherein the scanning accuracy is 4cm -1 Scanning range is 4000-400cm -1 Scanned 16 times.
2. Scanning Electron Microscope (SEM): the scanning electron microscope (model: FEI Verios G4U) was used for thermal field emission. And adhering the sample to a sample table through conductive adhesive, and performing surface metal spraying treatment. Scanning and imaging by using an electron beam with an accelerating voltage of 5kV, and observing the appearance of a sample.
3. Fire early warning test: connecting a sample with the size of 300mm multiplied by 50mm with a voltage alarm through a lead, then placing the sample at the position 20mm above the alcohol lamp, exposing the sample to the flame of the alcohol lamp with the height of 40mm, removing the flame after 20s, setting the early warning voltage to be 1mV, and recording the voltage curve and the early warning response time of the sample.
4. Vertical combustion test: samples of polyester film (size 50 mm. Times.100 mm. Times.25 μm), cotton fabric (size 76 mm. Times.300 mm. Times.1 mm) and polyurethane foam (size 125 mm. Times.13 mm. Times.3.2 mm) were placed vertically 19mm above the Bunsen burner, exposed to Bunsen burner flame of 40mm in height, and after 20 seconds the flame was removed, and the burning phenomena and data were recorded.
TABLE 1
TABLE 2
As can be seen from the data of examples 1 to 10 in tables 1 and 2, the layered bridging crosslinked heterostructure nano-coating with temperature sensing and flame retarding functions prepared under different process conditions can provide the polyester film, the cotton fabric, the polyurethane foam material and other flammable substrates with sensitive temperature sensing function and excellent flame retarding performance by using different organic thermoelectric monomers, surfactants, oxidants, viscous organic polymers, catalysts, crosslinking agents, layered conductive nano-materials and solvents.
From table 1 and fig. 4 to 6, it can be seen that the layered bridging cross-linked heterostructure nano-coating with temperature sensing and flame retarding functions provided by the invention can provide a sensitive, accurate and repeatable temperature sensing function for flammable substrates. As in example 1, on polyester film, cotton fabric and polyurethane foam materials, the fire early warning time of the nano coating when encountering open fire only needs 1.8s, 2.2s and 1.8s (see Table 1), and the maximum value of the output voltage signal can reach 5.6mV (see FIG. 4). In contrast, the fire pre-warning time of the nanocoating without the layered bridging cross-linked heterostructure (see comparative example 2) on the three flammable substrates was 5.4s, 7.2s and 5.8s (see table 1), respectively, and the maximum value of the output voltage signal was only 3.5mV (see fig. 4). Therefore, the layered bridging cross-linked heterostructure effectively improves the thermoelectric efficiency of the organic thermoelectric system. This is because: (1) The layered bridging cross-linked heterostructure provides an integrated conductive network, so that the conductivity of the organic thermoelectric system is improved; (2) The preparation method forms a rich heterogeneous interface, can scatter low-energy carriers and improves the Seebeck coefficient of an organic thermoelectric system; (2) The layered ordered structure can also scatter low-energy carriers and provide a high-speed transmission channel for high-energy carriers. Therefore, the nano coating provided by the invention can quickly generate carrier migration when encountering high temperature or open flame, output voltage signals and trigger a fire alarm device. In addition, the temperature sensing function of the nano coating can accurately monitor the temperature rising stage before the occurrence of a fire disaster. As shown in FIG. 5, the maximum output voltage of the coating is linearly related to the heat treatment temperature (U max = 0.01384T-0.708), the ambient temperature can be accurately detected according to the magnitude of the coating voltage signal. More importantly, the temperature detection function has good stability and repeatability. As shown in fig. 6, after the continuous 50-time cycle of "200 ℃ heat treatment-natural cooling", a stable linear function relationship between the output voltage signal and the heat treatment temperature is maintained. Therefore, the technology provided by the invention realizes high-sensitivity temperature transmission on an organic thermoelectric systemSense and fire early warning, and solves the problems that the traditional fire early warning coatings (such as CN108109317A, CN109593343A and Journal of Hazardous Materials 2021, 403:123645) of GO groups and the like are insensitive to low temperature and can not be reused.
Meanwhile, as can be seen from table 2, fig. 7 and 8, the layered bridging cross-linked heterostructure nano-coating with temperature sensing and flame retarding functions provided by the invention can endow the inflammable substrate with excellent flame retarding performance. As shown in table 2, the pure polyester film, the cotton fabric and the polyurethane foam (see comparative example 1) all belong to inflammable materials, and burn vigorously and burn out rapidly in the vertical burning test. In contrast, after the nano coating provided by the invention is coated, the flame retardant properties of the polyester film, the cotton fabric and the polyurethane foam material are all obviously improved, and the flame retardant is difficult to ignite and can self-extinguish in a vertical combustion test. This is because in the nanocoating provided by the invention, the layered conductive nanomaterial is ordered and the viscous organic hot wire nanowires bridge and crosslink them together to form a dense structure. The viscous organic hot wire nanowire contains abundant charring groups such as hydroxyl, amino, carboxyl and the like, and can be efficiently charred when encountering high temperature. The carbonized product adheres the thermally stable layered conductive nanomaterial together to form an internally porous (see fig. 8) and surface dense (see fig. 7) carbonized layer. The charring layer can play an excellent role in heat insulation and oxygen insulation, and the flame retardant property of the inflammable base material is obviously improved.
In summary, the coating provided by the invention overcomes the defects of the existing GO-based isothermal sensing coating, endows the inflammable substrate with sensitive, accurate and repeatable temperature sensing function and excellent flame retardant property, effectively improves the fire safety of the inflammable substrate, and has good intrinsic flexibility and adhesiveness, so that the coating has wide application prospect in the electrical field, particularly in flexible electronic equipment.
In summary, the foregoing description is only of the preferred embodiments of the present invention, and all equivalent changes and modifications made in accordance with the claims should be construed to fall within the scope of the invention.
Claims (10)
1. The preparation method of the layered bridging cross-linked heterostructure flexible nano coating is characterized by comprising the following steps of:
step (1) of preparing an organic thermoelectric nanowire dispersion, comprising the following steps:
step S11, adding a surfactant, an organic thermoelectric monomer and dopamine into a solvent A with the pH value of 1-5 to obtain a mixed solution A;
step S12, dropwise adding an oxidant solution into the mixed solution A for a mixed reaction for 6-24 hours to obtain a mixed reaction solution A;
step S13, centrifuging the mixed reaction solution A, washing the precipitate and uniformly dispersing the precipitate in the solvent B for standby, thus obtaining an organic thermoelectric nanowire dispersion liquid;
step (2) preparing viscous organic thermoelectric nanowires, comprising the following steps:
s21, adding a viscous organic polymer solution into the organic thermoelectric nanowire dispersion liquid obtained in the step (1);
s22, adding a catalyst, adjusting the reaction temperature to 40-120 ℃, and dripping a cross-linking agent solution into the mixture to carry out a cross-linking reaction for 4-24 hours to obtain a mixed reaction solution B;
step S23, centrifuging the mixed reaction liquid B, washing the precipitate and uniformly dispersing the precipitate in a solvent C for standby, thus obtaining viscous organic thermoelectric nanowire dispersion liquid;
step (3) preparing a layered bridging cross-linked heterostructure flexible nano-coating, which comprises the following steps:
step S31, dispersing the layered conductive nano material in a solvent C to prepare layered conductive nano material dispersion;
step S32, uniformly mixing the layered conductive nano material dispersion liquid with the viscous organic thermoelectric nano wire dispersion liquid obtained in the step (2) to obtain a mixed dispersion liquid;
and step S33, coating the mixed dispersion liquid on a flammable substrate, and drying to obtain the layered bridging cross-linked heterostructure flexible nano coating.
2. The method for preparing the layered bridging cross-linked heterostructure flexible nano-coating according to claim 1, wherein the method comprises the following steps: solvent A, solvent B and solvent C are one or more of deionized water, ethanol, acetonitrile, acetone, N-dimethylformamide, tetrahydrofuran, N-butanol and N-hexane.
3. The method for preparing the layered bridging cross-linked heterostructure flexible nano-coating according to claim 1 or2, characterized by:
the organic thermoelectric monomer in the step (1) is one or more of pyrrole, aniline, 3, 4-ethylene dioxythiophene and carbazole;
the surfactant is one or more of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, cetyltrimethylammonium bromide, sodium fatty alcohol polyoxyethylene ether sulfate and polyvinylpyrrolidone;
the oxidant solution is obtained by dissolving an oxidant in a solvent, wherein the oxidant is one or more of vanadium pentoxide, potassium dichromate, ferric chloride, ammonium persulfate, ferric nitrate, methyl triphenylphosphine persulfate and ferric p-toluenesulfonate.
4. The method for preparing the layered bridging cross-linked heterostructure flexible nano-coating according to claim 1 or2, characterized by:
the viscous organic polymer in the step (2) is one or more of polyvinyl alcohol, sodium alginate, cellulose acetate, carboxymethyl chitosan, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose;
the catalyst is one or more of sodium hypophosphite, sodium hydroxide and potassium hydroxide;
the cross-linking agent is one or more of glyoxal, glutaraldehyde, glyoxal, butane tetracarboxylic acid and epichlorohydrin.
5. The method for preparing the layered bridging cross-linked heterostructure flexible nano-coating according to claim 1 or2, characterized by:
the layered conductive nanomaterial in the step (3) is one or more of graphene nanoplatelets, graphene nanoribbons and MXene nanoplatelets.
6. The method for preparing the layered bridging cross-linked heterostructure flexible nano-coating according to claim 1 or2, characterized by:
in the step (1), the mass ratio of the surfactant to the organic thermoelectric monomer is 0.5:1-2:1, the mass ratio of the dopamine to the organic thermoelectric monomer is 0.5:1-2:1, and the mass ratio of the oxidant to the organic thermoelectric monomer is 2:1-8:1;
in the step (2), the mass ratio of the viscous organic polymer to the organic thermoelectric nano wire is 0.3:1-1.2:1, the mass ratio of the catalyst to the cross-linking agent is 1:1-3:1, and the mass ratio of the cross-linking agent to the viscous organic polymer is 0.05:1-0.4:1;
in the step (3), the mass ratio of the layered conductive nano material to the viscous organic thermoelectric nano wire in the mixed dispersion liquid is 0.25:1-4:1.
7. The method for preparing the layered bridging cross-linked heterostructure flexible nano-coating according to claim 1 or2, characterized by:
and (3) coating the mixed dispersion liquid on the inflammable base material for 1-24 times, wherein the coating adopts one or more of spraying, brushing and dip-coating, the coating amount of each spraying or brushing is 0.05-0.20mL/cm <2 >, and the soaking time period of each dip-coating is 0.5-10min.
8. The method for preparing the layered bridging cross-linked heterostructure flexible nano-coating according to claim 1 or2, characterized by: the mixed dispersion liquid in the step (3) is uniformly mixed by the combined action of one or two of stirring and ultrasonic treatment for 15-240 min.
9. The layered bridging crosslinking heterostructure flexible nano coating is characterized in that: a method for preparing the layered bridging cross-linked heterostructure flexible nano-coating according to any one of claims 1-8.
10. The application of the layered bridging cross-linked heterostructure flexible nano coating is characterized in that: the layered bridging cross-linked heterostructure flexible nano coating is applied to films, fabrics and polymer foam materials.
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