Janus cotton fabric with directional sweat and photothermal evaporation function and preparation method thereof

Abstract

The application discloses a Janus cotton fabric with directional sweat and photothermal evaporation functions and a preparation method thereof. The Janus cotton fabric is composed of a cotton fabric base, a photothermal layer arranged on the double-side surfaces of the cotton fabric base, and a hydrophobic layer arranged on the protruding part of the inner side of the cotton fabric base, wherein the hydrophobic layer is located on the surface of the photothermal layer; the inner side of the Janus cotton fabric is a structure with concave-convex alternation; the protruding part of the inner side of the Janus cotton fabric has hydrophobicity, and the concave part has hydrophilicity; and the outer side of the Janus cotton fabric has superhydrophilicity. The Janus cotton fabric provided by the application combines the photothermal conversion and the Janus characteristics together, the photothermal effect generated by the photothermal layer can quickly evaporate the sweat transported from the internal hydrophobic surface to the external superhydrophilic surface in a directional manner, so that the comfort during physical activity can be ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of functionalized Janus fabrics and personal thermal comfort management, and in particular to a Janus cotton fabric with directional sweat and photothermal evaporation functions and a preparation method thereof. BACKGROUND

[0002] Personal thermal comfort management is mainly related to sweat and temperature regulation. However, traditional fabrics have significant limitations in terms of sweat and moisture management. Especially during outdoor intense exercise, people often sweat a lot, causing the clothes to become wet quickly. This not only increases the discomfort of the human body, but also significantly reduces the cooling effect of the clothes. At the same time, due to the limited moisture transport performance of traditional fabrics, it is difficult to effectively transport sweat from the skin surface, further affecting the comfort of wearing.

[0003] In order to solve this problem, the fabric needs to meet two major requirements to achieve effective thermal management when sweating a lot: one is to be able to transport sweat on the skin to the environment in a directional manner, and the other is to be able to quickly evaporate the excess sweat accumulated in the clothes. Therefore, intelligent textiles with adjustable transport properties have gradually attracted attention and shown great potential in regulating the humidity and temperature of the microenvironment around the human skin. Among them, Janus fabric, as an innovative material with asymmetric wettability, provides an effective solution for directional sweat transport. This fabric is ingeniously composed of a thin hydrophobic layer and a hydrophilic layer, allowing water to be transported efficiently from the hydrophobic side to the hydrophilic side, while effectively preventing reverse transport. However, it is worth noting that in the case of heavy sweating, the Janus fabric may reach a saturation state, causing its liquid transport capacity to be blocked, which may not be able to continuously and effectively transport sweat from the skin surface, thereby affecting the comfort of the body. SUMMARY

[0004] In view of the deficiencies of the prior art, the first object of the present application is to provide a Janus cotton fabric with directional sweat and photothermal evaporation functions. The Janus cotton fabric provided by the present application combines photothermal conversion with Janus properties. The photothermal effect generated by the photothermal coating quickly evaporates the sweat transported from the internal hydrophobic surface to the external superhydrophilic surface in a directional manner, thereby ensuring comfort during physical activity to promote personal thermal management, making it an ideal choice for thermal management in high-intensity sports activities.

[0005] The second object of the present application is to provide a preparation method of a Janus cotton fabric with directional sweat and photothermal evaporation functions.

[0006] In order to achieve the above-mentioned objects, the present application adopts the following technical solutions:

[0007] The Janus cotton fabric with directional sweat and photothermal evaporation functions is composed of a cotton fabric base, a photothermal layer arranged on the double-side surface of the cotton fabric base, and a hydrophobic layer arranged on the raised part of the inner side of the cotton fabric base, wherein the hydrophobic layer is located on the surface of the photothermal layer; and the inner side of the Janus cotton fabric is a structure with concave-convex alternation.

[0008] The Janus cotton fabric combines the conversion of photothermal and Janus characteristics together, and under the action of the Janus characteristics, can realize the directional transportation of sweat from the hydrophobic side to the hydrophilic side, and under the light, the photothermal effect generated by the photothermal layer can generate a local high temperature up to 39.8℃, and can accelerate the rate of one-way drainage by promoting the evaporation rate, so as to ensure the comfort during physical activity. In the present application, the inner side of the Janus cotton fabric refers to the contact surface with the skin in the actual application process.

[0009] Preferably, the photothermal layer is a polyacrylic acid (PAA) / polypyrrole (PPy) nanoparticle composite coating.

[0010] Preferably, the hydrophobic layer is a PDMS film.

[0011] Preferably, the raised part of the inner side of the Janus cotton fabric has hydrophobicity, the recessed part has hydrophilicity, and the outer side of the Janus cotton fabric has superhydrophilicity. The inner side of the Janus cotton fabric of the present application has a concave-convex alternation structure in microcosm, wherein the raised part has hydrophobicity due to the arrangement of the hydrophobic layer, and the recessed part has hydrophilicity. The hydrophobic-hydrophilic structure has a wetting gradient, generates a Laplace pressure difference, drives the directional transportation of liquid, and further accelerates the discharge of sweat.

[0012] The preparation method of the Janus cotton fabric with directional sweat and photothermal evaporation functions comprises the following steps: pretreating a cotton fabric to obtain a pretreated cotton fabric, then immersing the pretreated cotton fabric in a silane solution to obtain a silane-treated cotton fabric, then immersing the silane-treated cotton fabric in a polyacrylic acid (PAA) solution and a polypyrrole (PPy) nanoparticle solution in sequence to obtain a cotton fabric with a photothermal layer, then performing wetting treatment on the cotton fabric with the photothermal layer by using a sodium chloride aqueous solution, and finally dropping a PDMS-containing mixed liquid on the inner side surface of the cotton fabric with the photothermal layer and performing drying treatment, so as to obtain the Janus cotton fabric with directional sweat and photothermal evaporation functions.

[0013] The preparation method of the application has excellent hydrophilicity with cotton fabric as the substrate, the hydrophilicity of the cotton fabric is further improved by pretreatment, then the cotton fabric is treated with a silane solution, so that the cotton fabric is modified to have positive charges, then, the positively charged polypyrrole (PPy) nanoparticles and the negatively charged polyacrylic acid (PAA) are assembled by electrostatic attraction as the material, finally, the PAA with negative charges and the PPy nanoparticles with positive charges are prepared as a light-thermal surface by LBL assembly. Then, the n-hexane mixed solution of polydimethylsiloxane (PDMS) and a curing agent is dropped on the inner side surface of the cotton fabric with the light-thermal layer wetted by the sodium chloride aqueous solution, by virtue of the immiscibility of the aqueous solution and the n-hexane, the volatility of the n-hexane, and the density of the sodium chloride aqueous solution being greater than that of the polydimethylsiloxane (PDMS), the PDMS is successfully aggregated and deposited on the protruding part of one side of the cotton fabric to form a hydrophobic-hydrophilic structure with the recessed part, and the hydrophobic modification of the cotton fabric on one side is flexibly realized, while the outer side surface is not subjected to the hydrophobic modification and still maintains the superhydrophilicity, so that the inner side has a hydrophobic-hydrophilic interlaced structure and the outer side has a superhydrophilic structure.

[0014] Preferably, the pretreatment process of the cotton fabric is that the cotton fabric is immersed in the NaOH aqueous solution with a pH of 8-10, the immersion temperature is controlled to be 60-90 DEG C, and the immersion time is 1-2 h.

[0015] In actual operation, after the cotton fabric is immersed, the cotton fabric is taken out with tweezers, washed with anhydrous ethanol and ultrapure water under ultrasonic conditions, so as to clean the excess NaOH on the surface of the initial cotton fabric, and then dried with a hair dryer to obtain the pretreated cotton fabric for standby use. In the application, the initial cotton fabric is treated by strong alkali immersion, so as to activate the hydroxyl groups on the surface of the initial cotton fabric, so that the initial cotton fabric has better hydrophilicity, and the roughness of the surface of the initial cotton fabric is increased, so that the PDMS can be better attached to the surface of the initial cotton fabric.

[0016] Preferably, the silane solution is mixed by water, acetic acid solution and 3-aminopropyl triethoxysilane, and the mass fraction of 3-aminopropyl triethoxysilane in the silane solution is 1-5 wt%, and the volume ratio of water to acetic acid solution is 500 ml: 100-500 μl.

[0017] Further preferably, the pH of the acetic acid solution is 2-4.

[0018] Preferably, the pretreated cotton fabric is immersed in the silane solution for 1-2 h, and then dried to obtain the silane-treated cotton fabric.

[0019] In actual operation, after the pretreated cotton fabric is immersed in the silane solution, it is taken out with tweezers, rinsed in ethanol, and then dried with a hair dryer to completely dry the cotton fabric, which is ready for use. The purpose is to make the surface of the cotton fabric positively charged.

[0020] Preferably, the mass fraction of polyacrylic acid (PAA) in the polyacrylic acid (PAA) solution is 1-5wt%. In actual operation, taking 1% polyacrylic acid (PAA) solution as an example, 1g of polyacrylic acid is weighed and added to a beaker containing 100ml of ultrapure water.

[0021] Preferably, the polyacrylic acid (PAA) solution is obtained by dissolving PVA in water to obtain a PVA solution, then adding ferric chloride hexahydrate to the PVA solution to obtain a mixture, and then adding pyrrole to the mixture to obtain the polyacrylic acid (PAA) solution.

[0022] The mass fraction of PVA in the PVA solution is 1-3.5wt%.

[0023] The solid-liquid mass volume ratio of ferric chloride hexahydrate to water is 0.5-2g:100ml.

[0024] The volume ratio of pyrrole to water is 0.5-2:100ml.

[0025] Preferably, the silane-treated cotton fabric is immersed in the polyacrylic acid (PAA) solution for 5-30min, then taken out and immersed in the polyacrylic acid (PAA) solution for 5-30min, and then dried to obtain a cotton fabric with a photo-thermal layer.

[0026] In actual operation, the prepared pretreated cotton fabric is immersed in the PAA solution, taken out after soaking, and hung to form a thin layer of water film on the surface. Then it is immersed in the PPy solution, taken out, and dried in an electric heating air drying oven for 0.5h at 70℃. After complete drying, a cotton fabric with a photo-thermal layer is obtained.

[0027] Preferably, the mass fraction of sodium chloride in the sodium chloride aqueous solution is ≤26.4%, preferably 9-26.4%, and further preferably 18-26.4%. The inventors found that within the above range, as the content of sodium chloride increases, the density difference between PDMS and the sodium chloride aqueous solution becomes larger, more PDMS gathers on the convex part of one side of the cotton fabric, the penetration time of water droplets from hydrophobic to hydrophilic is accelerated, and the Janus effect of the cotton fabric is enhanced.

[0028] Preferably, the amount of the sodium chloride aqueous solution added to each 4cmX4cm cotton fabric is 100-400ul, preferably 250-400ul. The amount of the sodium chloride aqueous solution is controlled in the upper range, and the performance of the final cotton fabric is optimal.

[0029] Preferably, the PDMS-containing mixed solution is obtained by mixing polydimethylsiloxane (PDMS), a curing agent, and n-hexane, wherein the mass ratio of PDMS to the curing agent is 0.8-1:0.1, and the solid-liquid mass volume ratio of PDMS to n-hexane is 0.06-1g:10ml.

[0030] In actual operation, the PDMS-containing mixed solution can be obtained by adding 0.7g of PDMS and 0.07g of a curing agent to 10ml of n-hexane, and stirring for 10min to obtain the PDMS solution.

[0031] In the present application, the total type of the curing agent is not limited, and the curing agents for PDMS described in the prior art can be used.

[0032] Further preferably, the curing agent is a commercially available Dow Corning 184 curing agent. The Dow Corning 184 curing agent can be used in combination with the PDMS to form a network structure, so that the PDMS and the curing agent are hardened when mixed.

[0033] In actual operation, the cotton fabric with a photothermal layer is clamped and fixed on a manual displacement table, the NaCl aqueous solution is uniformly dropped on the surface of the obtained cotton fabric with a photothermal layer using a pipette to form a water film, and then the PDMS mixed solution is uniformly dropped on the water film using a pipette. When the NaCl aqueous solution is dropped on the water film to form a water film and the PDMS mixed solution is dropped, attention should be paid to the experimental operation to prevent the water film formed by the NaCl aqueous solution from being pierced, so as to prevent the PDMS from penetrating to the other side of the cotton fabric. After the n-hexane is completely volatilized, heating treatment is carried out under a hair dryer, and after the cotton fabric is completely dried, a coated cotton fabric is obtained.

[0034] Finally, the coated cotton fabric is placed in an electric heating air drying oven for drying treatment, and after drying, it is placed in ultrapure water for ultrasonic cleaning to obtain the Janus cotton fabric with directional perspiration and photothermal evaporation functions.

[0035] The purpose of the drying treatment is to better cure and adhere the PDMS on the surface of the coated cotton fabric, and the purpose of the ultrasonic cleaning is to clean the sodium chloride particles on the surface of the coated cotton fabric. The temperature of the drying treatment is 90℃, and the time is 0.5h. The ultrasonic cleaning time is 1min.

[0036] Preferably, the cotton fabric is kept in a horizontal state during the drying process. After the n-hexane is completely volatilized, the cotton fabric is heated under a hair dryer, which is kept in a horizontal state to avoid affecting the aggregation of the PDMS.

[0037] Principle and advantage

[0038] The application provides a Janus cotton fabric with directional sweat and photothermal evaporation functions, which is composed of a cotton fabric base, a photothermal layer arranged on the double-sided surface of the cotton fabric base, and a hydrophilic layer arranged on the outer side of the cotton fabric base, wherein the hydrophilic layer is located on the surface of the photothermal layer; the inner side of the Janus cotton fabric is a structure with concave-convex alternation, wherein the convex part of the inner side of the Janus cotton fabric has hydrophobicity, and the concave part has hydrophilicity; and the outer side of the Janus cotton fabric has superhydrophilicity.

[0039] The Janus cotton fabric provided by the application combines photothermal conversion and Janus characteristics together, and the photothermal effect generated by the photothermal layer can quickly evaporate sweat transported from the internal hydrophobic surface to the external superhydrophilic surface, so that the comfort during physical activity can be ensured.

[0040] In the preparation method of the application, a photothermal surface composed of photothermal nanomaterials (polypyrrole (PPy) nanoparticles) and polyelectrolytes (polyacrylic acid) is first constructed on the surface of the cotton fabric base. In the application, the pretreated cotton fabric is first treated with a silane solution to obtain a positive charge modification, and then, the positively charged polypyrrole (PPy) nanoparticles and the negatively charged polyacrylic acid (PAA) are assembled by electrostatic attraction as material assembly. Finally, a negatively charged PAA and a positively charged PPy nanoparticle coating are prepared as a photothermal surface through LBL assembly.

[0041] However, in order to construct a hydrophobic-hydrophilic structure, in the application, a n-hexane mixed solution of polydimethylsiloxane (PDMS) and a curing agent is dropped on the surface of the cotton fabric with the photothermal layer wetted by a sodium chloride aqueous solution. By taking advantage of the mutual insolubility of the aqueous solution and n-hexane, the easy volatilization of n-hexane, and the fact that the density of the sodium chloride aqueous solution is greater than that of polydimethylsiloxane (PDMS), the PDMS is successfully aggregated and deposited on the convex part of one side of the cotton fabric to form a hydrophobic-hydrophilic structure with the concave part, and the hydrophobic modification of the single side of the cotton fabric is flexibly realized.

[0042] In the process of preparing the hydrophobic-hydrophilic structure, in one aspect, the sodium chloride particles are used to increase the density of the aqueous solution, because the density of polydimethylsiloxane (PDMS) is slightly smaller than that of water, due to the action of capillary force, on the water film on the surface of the cotton fabric, the PDMS will climb from the central concave part to the surrounding convex part of the water film, on the other hand, by heating and drying, a temperature gradient is formed on the surface of the water film, in addition, because the water solution on the convex part of the cotton fabric is closer to the cotton fibers, the evaporation rate of the part close to the fibers is fast, with the volatilization of n-hexane, the heat absorption of evaporation, so the temperature of the convex part is lower than that of the concave part, and the surface tension is high, after the aqueous solution is completely heated and evaporated, finally, the PDMS will gather in the convex part of the cotton fabric, so that the convex part has hydrophobicity, and the concave part has hydrophilic structure, thereby forming a hydrophobic-hydrophilic structure with the concave part.

[0043] The method provided by the application is simple to operate and easy to implement, and does not cause secondary pollution to the environment. The photo-thermal coating of the Janus cotton fabric with directional sweat and photo-thermal evaporation functions prepared by the method has good photo-thermal performance and can convert solar energy into heat energy. The coating manufactured by LBL assembly has the advantages of simplicity and low cost. The hydrophobic gradient of the Janus cotton fabric with directional sweat and photo-thermal evaporation functions prepared by the method decreases from the hydrophobicity of the side on which liquid is dropped to the superhydrophilicity of the side on which liquid is not dropped. One side of the Janus cotton fabric with directional sweat and photo-thermal evaporation functions obtained by modification is a hydrophobic-hydrophilic structure, and the other side is a superhydrophilic structure. The Janus cotton fabric with directional sweat and photo-thermal evaporation functions can direct sweat through the Janus structure and remove excessive sweat through solar evaporation to keep the skin dry. In addition, it also helps to keep the skin temperature within a normal range and prevent hypothermia caused by excessive sweating. The solar-driven evaporation realized by the photo-thermal coating provides driving force for the directional transport of sweat from the internal hydrophobic surface to the external superhydrophilic surface. These characteristics can ensure comfort during physical activity. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The preparation process flowchart of the method for preparing the Janus cotton fabric with directional sweat and photo-thermal evaporation functions.

[0045] Figure 2 The structure schematic diagram of the cotton fabric prepared in Example 1.

[0046] Figure 3 The preparation process schematic diagram of the polypyrrole nanoparticle solution in Example 1.

[0047] Figure 4Schematic diagram of the preparation process of the photothermal layer of the cotton fabric in Example 1, which is composed of photothermal nanomaterials and polyelectrolytes; positively charged polypyrrole (PPy) nanoparticles and negatively charged polyacrylic acid (PAA) are assembled by electrostatic attraction, and the substrate is initially modified with a positively charged chemical. Subsequently, a coating of negatively charged PAA and positively charged PPy nanoparticles is prepared by LBL assembly.

[0048] Figure 5 Schematic diagram of the preparation of the Janus cotton fabric in Example 1 with a hydrophobic-hydrophilic phase interfacial structure; the principle is capillary force driven: sodium chloride particles are added to increase the density of the aqueous solution, because the density of polydimethylsiloxane (PDMS) is slightly less than that of water, and due to the action of capillary force, PDMS will climb from the central concave part to the surrounding convex part on the water film on the surface of the cotton fabric.

[0049] Figure 6 Flowchart of the preparation of the Janus cotton fabric in Example 1 with a hydrophobic / hydrophilic phase interfacial-superhydrophilic structure; hot air is used for heating and drying, forming a temperature gradient on the surface of the water film, in addition, because the convex part of the cotton fabric on one side is closer to the cotton fibers, the part close to the fibers evaporates faster, and as n-hexane evaporates, the evaporation is endothermic, so the temperature of the convex part is lower than that of the concave part, and the surface tension is higher. After the aqueous solution is completely heated and evaporated, finally, PDMS will gather in the convex part of the cotton fabric, forming a hydrophobic-hydrophilic structure with the concave part, and the other side of the cotton fabric is a superhydrophilic structure.

[0050] Figure 7 Schematic diagram of the directional transport function of the Janus cotton fabric in Example 1.

[0051] Figure 8 Photothermal warming effect diagram of the Janus cotton fabric in Example 1 under the irradiation of a xenon lamp light source with a wavelength of 350 nm-780 nm.

[0052] Figure 9 Evaporation rate diagram of the Janus cotton fabric in Example 1.

[0053] Figure 10 Evaporation mass diagram of the Janus cotton fabric in Example 1. DETAILED DESCRIPTION

[0054] Example 1

[0055] A method for preparing a Janus cotton fabric with directional sweat and photothermal evaporation functions, as shown in Figure 1 , which comprises the following steps:

[0056] 1) Cut the initial cotton fabric to 4 cm X 4 cm, as shown in Figure 2As shown, the initial cotton fabric is completely immersed in NaOH with pH = 10 in a water bath, the immersion time is 1 h, and the temperature is 60°C. After 1 h, the initial cotton fabric is taken out with tweezers, washed with anhydrous ethanol and ultrapure water under ultrasonic conditions, in order to clean the excess NaOH on the surface of the initial cotton fabric, and then dried with a hair dryer to obtain a pretreated cotton fabric for standby use;

[0057] 2) First, prepare a polyvinyl alcohol (PVA) precursor solution, dissolve 1 g of PVA in 100 ml of water, magnetically stir and heat to 90°C to form a transparent solution. After the PVA solution is cooled to room temperature, 1 g of ferric chloride hexahydrate is added. Then, 1 ml of pyrrole is slowly injected under magnetic stirring, the solution immediately turns black, and is stored overnight to obtain a polypyrrole (PPy) nanoparticle solution, as shown in Figure 3 ;

[0058] 3) Weigh 1 g of polyacrylic acid into a beaker containing 100 ml of ultrapure water to obtain a PAA (polyacrylic acid) solution (1 wt%);

[0059] 4) Measure 500 ml of deionized water, 100 ul of acetic acid (pH = 3) and 1 wt% of 3-aminopropyl triethoxysilane, mix the three solutions to obtain a silane solution;

[0060] 5) Put the pretreated cotton fabric into the silane solution for 1 h, then take it out with tweezers and wash it in anhydrous ethanol, then dry it with a hair dryer to completely dry the cotton fabric, and then put it into the PPy solution for 5 min, take it out, and hang it to form a thin layer of water film on its surface, then put it into the PPy solution for 5 min, keep it evenly immersed, take it out, and put it into an electric heating air drying oven for drying treatment, the time is 0.5 h, and the temperature is 70°C, after completely drying, the cotton fabric with a photo-thermal layer is obtained, as shown in Figure 4 ;

[0061] 6) Weigh 0.07 g of PDMS and 0.007 g of curing agent into a 15 ml test tube, then add 10 ml of n-hexane, and stir with a magnetic stirrer to obtain a PDMS mixed solution;

[0062] 7) Weigh 2.64 g of NaCl into a 50 ml test tube, then add 10 ml of ultrapure water, and stir with a magnetic stirrer to obtain a NaCl aqueous solution;

[0063] 8), clamp and fix the cotton fabric with the photothermal layer on the manual displacement table, first use the pipette to evenly drop 400 μl of NaCl aqueous solution on the surface of the obtained cotton fabric with the photothermal layer, form a water film, then use the pipette to evenly drop 80 μl of PDMS mixed solution on the water film, after the n-hexane is completely volatilized, place it under the hair dryer for heating treatment for 2 min, after the cotton fabric is completely dried, obtain the coated cotton fabric;

[0064] 9), place the coated cotton fabric in a 90°C electric heating air drying oven for drying treatment for 0.5 h, after drying, place it in ultrapure water in an ultrasonic cleaning machine for ultrasonic cleaning for 1 min, obtain the Janus cotton fabric with the directional sweat releasing and photothermal evaporation function.

[0065] Performance detection

[0066] 1) Hydrophilic and hydrophobic performance detection

[0067] This example provides a unidirectional transport performance test of the Janus cotton fabric prepared by the preparation method of the Janus cotton fabric with the directional sweat releasing and photothermal evaporation function, by dropping liquid drops on different sides of the Janus cotton fabric, the transport behavior of water on it is studied. The dynamic transport process of the liquid drops on the Janus cotton fabric is monitored by a contact angle tester. As shown in Figure 7 , when the hydrophobic side is placed upward, the liquid drops are on the hydrophobic side, the liquid drops quickly pass through the hydrophilic side and wet the hydrophilic side within 22 s, leaving a dry hydrophobic surface. On the contrary, when the hydrophilic side is placed upward, the liquid drops quickly disperse on the hydrophilic surface, while being blocked by the hydrophobic side.

[0068] The initial water contact angle of one side of the Janus cotton fabric prepared in this example is 136°, showing high hydrophobicity, and the water contact angle of the other side is 0°, showing superhydrophilicity. Figure 7 The process of transporting water drops on the Janus cotton fabric from the hydrophobic side to the superhydrophilic side and from the superhydrophilic side to the hydrophobic side is shown. From Figure 7 It can be seen that the Janus cotton fabric has the function of unidirectional transport of water drops, the water drops spontaneously transport from the hydrophobic side to the superhydrophilic side at 22 s, but are blocked by the superhydrophilic side in the opposite direction and cannot be transported.

[0069] 2) Photothermal warming performance test

[0070] The light-thermal heating of the Janus cotton fabric was tested, and the temperature change of the Janus cotton fabric was measured by a thermal imager. The ordinary cotton fabric and the Janus cotton fabric with a light-thermal layer were respectively soaked in water for 20s, placed on a constant temperature heating table at 37.5℃, irradiated with a 350nm-780nm xenon lamp light source for 1min, and the temperature change was recorded by a thermal imager. The ordinary cotton fabric and the Janus cotton fabric with a light-thermal layer were respectively irradiated with a 350nm-780nm xenon lamp light source for 1min, and the temperature change was recorded by a thermal imager, as shown in Figure 8 , the ordinary cotton fabric did not show obvious heating effect, while the temperature of the Janus cotton fabric with a light-thermal layer rapidly increased, and the temperature could reach 39.8℃, and the light-thermal effect was also exhibited after wetting.

[0071] 3) The Janus cotton fabric of Example 1 was tested for the rate of simulated human skin surface water evaporation.

[0072] 400 microliters of water droplets were respectively taken by a syringe and dropped on the hydrophilic surface of the 4x4cm 2 ordinary cotton fabric, Janus cotton fabric and light-thermal Janus cotton fabric, which were not disturbed for a certain period of time to make the various cotton fabrics absorb water to reach equilibrium. Subsequently, the hydrophilic surface was placed upward and the hydrophobic surface was placed downward on a constant temperature heating table at 37.5℃, and a 350nm-780nm xenon lamp light source was placed above the cotton fabric. Under the irradiation of the 350nm-780nm xenon lamp light source, the mass of the cotton fabric was recorded by a balance for 4min. After 4min of irradiation of the xenon lamp light source, the mass change of the light-thermal Janus cotton fabric group was the largest, with a mass decrease of 0.012g cm -2 , the mass decrease of the ordinary cotton fabric group was 0.008 g cm -2 , and the mass decrease of the light-thermal Janus cotton fabric group was 1.5 times that of the ordinary cotton fabric group, as shown in Figure 9 . In addition, the evaporation rate value of the light-thermal Janus cotton fabric group was 0.181g cm -2 h -1 , which was higher than that of the ordinary cotton fabric group of 0.117 g cm -2 h -1 , as shown in Figure 10 , which showed that it had light-thermal conversion capability, could absorb sunlight and convert it into heat, and could accelerate the evaporation process of water.

[0073] Under the same conditions as in Example 1, only the content of sodium chloride and the amount of sodium chloride aqueous solution were changed, and the directional transport effect of the obtained Janus cotton fabric was as shown in Table 1.

[0074]

[0075] As can be seen from Table 1, with the increase of the content of sodium chloride, the transport time of water droplets is shortened, thereby indicating that the directional transport effect of the Janus cotton fabric is enhanced; at the same time, with the increase of the amount of the sodium chloride aqueous solution, the bending degree of the water film on one side of the Janus cotton fabric is reduced, and the PDMS is more likely to gather in the convex part, thereby the hydrophobicity of this side of the Janus cotton fabric is stronger, the difference in wettability between the two sides of the Janus cotton fabric is larger, and the directional transport effect of the Janus cotton fabric is stronger; the transport time of the second water droplet is shorter than that of the first water droplet, which indicates that the prepared Janus cotton fabric achieves the Janus effect; the less the amount of the sodium chloride aqueous solution, the greater the bending degree of the water film, and the more difficult the PDMS is to gather in the convex part, and the worse the directional transport effect of the Janus cotton fabric, thereby the longer the transport time of the water droplet; the lower the content of sodium chloride, the smaller the density difference between the sodium chloride aqueous solution and the PDMS, and the more difficult the PDMS is to climb to the convex part, thereby affecting the hydrophobicity of the Janus cotton fabric, leading to the worse directional transport effect of the Janus cotton fabric and the longer transport time of the water droplet.

Claims

1. A Janus cotton fabric with directional perspiration and photothermal evaporation functions, characterized in that: The Janus cotton fabric is composed of a cotton fabric base, a photothermal layer arranged on both sides of the cotton fabric base, and a hydrophobic layer arranged on the protruding part of the inner side of the cotton fabric base, wherein the hydrophobic layer is located on the surface of the photothermal layer; the inner side of the Janus cotton fabric is a structure with concave-convex alternation. The preparation method of the Janus cotton fabric is as follows: The cotton fabric is pretreated to obtain pretreated cotton fabric, then the pretreated cotton fabric is immersed in a silane solution to obtain silane-treated cotton fabric, then the silane-treated cotton fabric is sequentially immersed in a PAA solution and a PPy nanoparticle solution to obtain cotton fabric with a photothermal layer, then the cotton fabric with the photothermal layer is subjected to wetting treatment with a sodium chloride aqueous solution, and finally a mixed solution containing PDMS is dropped on the inner side surface of the cotton fabric with the photothermal layer, and drying treatment is performed, thereby obtaining Janus cotton fabric with directional perspiration and photothermal evaporation functions. The silane solution is prepared by mixing water, acetic acid solution and 3-aminopropyl triethoxysilane, wherein the mass fraction of 3-aminopropyl triethoxysilane in the silane solution is 1-5 wt%, and the volume ratio of water to acetic acid solution is 500 ml:100-500 μl. The pH of the acetic acid solution is 2-4. The pretreated cotton fabric is immersed in the silane solution for 1-2 h, and then dried to obtain the silane-treated cotton fabric. In the sodium chloride aqueous solution, the mass fraction of sodium chloride is ≤26.4%. The amount of the sodium chloride aqueous solution dropped on the cotton fabric per 4 cmX4 cm is 100-400 μl. The method for obtaining the mixed solution containing PDMS is as follows: PDMS, a curing agent and n-hexane are mixed to obtain the mixed solution, wherein the mass ratio of PDMS to the curing agent is 0.8-1:0.1, and the solid-liquid mass volume ratio of PDMS to n-hexane is 0.06-1 g:10 ml.

2. The Janus cotton fabric with directional perspiration and photothermal evaporation function according to claim 1, characterized in that: The photothermal layer is a PAA / PPy nanoparticle composite coating. The hydrophobic layer is a PDMS film.

3. The Janus cotton fabric with directional perspiration and photothermal evaporation function according to claim 1 or 2, characterized in that: The protruding part of the inner side of the Janus cotton fabric has hydrophobicity, and the recessed part has hydrophilicity; the outer side of the Janus cotton fabric has superhydrophilicity.

4. The method for preparing the Janus cotton fabric with directional perspiration and photothermal evaporation function according to claim 1 or 2, characterized in that: The pretreated cotton fabric is immersed in a silane solution to obtain silane-treated cotton fabric, then the silane-treated cotton fabric is sequentially immersed in a PAA solution and a PPy nanoparticle solution to obtain cotton fabric with a photothermal layer, then the cotton fabric with the photothermal layer is subjected to wetting treatment with a sodium chloride aqueous solution, and finally a mixed solution containing PDMS is dropped on the inner side surface of the cotton fabric with the photothermal layer, and drying treatment is performed, thereby obtaining Janus cotton fabric with directional perspiration and photothermal evaporation functions.

5. The method for preparing a Janus cotton fabric with directional perspiration and photothermal evaporation functions according to claim 4, characterized in that: The pretreatment process of the cotton fabric is as follows: the cotton fabric is immersed in a NaOH aqueous solution with a pH of 8-10, the immersion temperature is controlled at 60-90℃, and the immersion time is 1-2 h.

6. The method for preparing a Janus cotton fabric with directional perspiration and photothermal evaporation functions according to claim 4, characterized in that: The silane solution is mixed by water, acetic acid solution and 3-aminopropyl triethoxysilane, wherein the mass fraction of 3-aminopropyl triethoxysilane in the silane solution is 1-5wt%, the volume ratio of water to acetic acid solution is 500ml:100-500ul; The pH of the acetic acid solution is 2-4; The pretreated cotton fabric is immersed in the silane solution for 1-2h, and then dried to obtain the silane treated cotton fabric.

7. The method for preparing a Janus cotton fabric with directional perspiration and photothermal evaporation functions according to claim 4, characterized in that: The mass fraction of PAA in the PAA solution is 1-5wt%; The PPy nanoparticle solution is obtained by the following process: dissolving PVA in water to obtain a PVA solution, then adding ferric chloride hexahydrate into the PVA solution to obtain a mixed solution, adding pyrrole into the mixed solution, and then polymerization reaction is carried out; The mass fraction of PVA in the PVA solution is 1-3.5wt%; The solid-liquid mass volume ratio of ferric chloride hexahydrate to water is 0.5-2g:100ml; The volume ratio of pyrrole to water is 0.5-2:100ml; The silane treated cotton fabric is immersed in the PAA solution, taken out after 5-30min, then immersed in the PPy nanoparticle solution for 5-30min, and dried to obtain the cotton fabric with a photothermal layer.

8. The method for preparing a Janus cotton fabric with directional perspiration and photothermal evaporation functions according to claim 4, characterized in that: The mass fraction of sodium chloride in the sodium chloride aqueous solution is ≤26.4%. The amount of sodium chloride aqueous solution added per 4cmX4cm of cotton fabric is 100-400ul.

9. The method for preparing a Janus cotton fabric with directional perspiration and photothermal evaporation functions according to claim 4, characterized in that: The method for obtaining the mixed solution containing PDMS is mixing PDMS, curing agent and n-hexane, wherein the mass ratio of PDMS to curing agent is 0.8-1:0.1, and the solid-liquid mass volume ratio of PDMS to n-hexane is 0.06-1g:10ml.

10. The method of claim 4, wherein the Janus cotton fabric having directional perspiration and photothermal evaporation functions is characterized by: During the drying process, the cotton fabric is kept in a horizontal state.

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