Self-healing functional super-hydrophobic cotton fabric and preparation method thereof

Abstract

The application discloses a self-healing functional super-hydrophobic cotton fabric and a preparation method thereof, and belongs to the technical field of cotton fabrics. The specific structure comprises a cotton fabric substrate, wherein micron and nanometer silica particles and polydimethylsiloxane are dispersed in the cotton fabric substrate, and the mixing mass ratio of the micron and nanometer silica particles is 1:1. The specific method is as follows: micron silica particles, nanometer silica particles, polydimethylsiloxane and a curing agent thereof are dispersed in anhydrous ethanol by magnetic stirring to form a solution A; the cotton fabric is ultrasonically immersed in the solution A for coating, and finally dried at 60-80 DEG C to obtain the self-healing functional super-hydrophobic cotton fabric. The super-hydrophobic cotton fabric has the self-healing function. When the super-hydrophobic surface is abraded and damaged to reduce the super-hydrophobicity, the super-hydrophobicity can be repaired by heating at 80-120 DEG C for 15-30 min, and the micro-nano structure and low surface energy of the super-hydrophobic surface are also repaired. The super-hydrophobic cotton fabric also has the self-cleaning property.

Description

Technical Field

[0001] This invention belongs to the field of cotton fabric technology, and relates to a self-healing superhydrophobic cotton fabric, as well as a method for preparing the self-healing superhydrophobic cotton fabric. Background Technology

[0002] Superhydrophobic materials possess exceptional water resistance due to their unique "lotus leaf effect." The air layer formed by the substrate material effectively isolates the superhydrophobic surface from external substances, granting it self-cleaning, anti-fouling, anti-icing, antibacterial, and anti-corrosion properties, leading to its widespread application in medical, daily life, and military fields. Superhydrophobic surfaces are typically prepared through low surface energy modification and the construction of micro / nano rough structures. Nanoparticles are often used to construct these micro / nano rough structures, which are then modified with low surface energy materials such as fluorosilanes and polytetrafluoroethylene to achieve superhydrophobicity. However, the micro / nano rough structures formed by nanoparticles are easily damaged under extreme external conditions, and the surface energy increases, causing the surface to lose its superhydrophobicity.

[0003] Developing durable superhydrophobic surfaces has become a key focus and challenge for future development. Current research has utilized the strong adhesive properties of epoxy resin to prepare wear-resistant superhydrophobic materials. Superhydrophobic cotton fabrics with intelligent self-healing capabilities can permanently recover their original shape from a temporary state when exposed to light, electromagnetic welding, magnetic welding, or moisture. However, existing methods for preparing self-healing superhydrophobic surfaces are complex, and the long self-healing time and demanding conditions limit their practical application.

[0004] By mimicking the microscopic structures of plants and animals such as butterfly wings, spider silk, rose petals, and gecko feet, superhydrophobic surfaces have been prepared for applications such as anti-icing, corrosion prevention, self-cleaning, and antibacterial properties. It is well known that obtaining a superhydrophobic surface requires two conditions: (1) a micro / nano rough structure; and (2) low surface energy. This is achieved through one or two steps, such as spraying, chemical etching, impregnation, or hydrothermal techniques. However, due to poor adhesion between the coating and the substrate, poor resistance to mechanical wear, and poor chemical stability, superhydrophobic surfaces are difficult to apply in the long term. A new concept based on a superhydrophobic surface / interface with intelligent self-healing capabilities has emerged, showing potential for commercial production. Currently, the realization of self-healing superhydrophobic surfaces mainly relies on two strategies: one is to store a low surface energy agent in the substrate. After the surface layer is damaged, the low surface energy decreases, and heating allows the low surface energy stored in the substrate to migrate to the surface layer, thus reconstructing the self-healing superhydrophobic surface. The literature “Ge MZ,Cao CY,Liang FH,Liu R.,Zhang Y.,Zhang W.,Zhu TX,Yi B.,Tang YX,Lai YKA”PDMS-in-water emulsion enables mechanochemically robust superhydrophobic surfaces with self-healing nature[J].NanoscaleHorizons,2020,5(1):65-73” describes the preparation of a superhydrophobic cotton fabric with intelligent self-healing properties by uniformly dispersing PDMS in water to form an emulsion, which is then coated onto cotton textiles. During coating, PDMS enters the internal space of the cotton fibers. After evaporation, PDMS molecules are grafted onto the outer surface of the cotton fibers through strong binding forces. When the surface is abraded by sandpaper, the PDMS on the surface layer decreases, and the micro-nano structure weakens. After heating at 80℃ for 30 minutes, the PDMS stored inside the substrate diffuses to the surface layer upon heating, regaining high surface energy. Another type relies on shape memory polymers (SMPs), a class of smart materials that, when exposed to appropriate stimuli such as heat, light, electromagnetic welding, magnetic welding, or moisture, are able to permanently recover their original shape from a temporary shape.The literature “Guo XJ, Xue CH, Sathasivam S., Page K., He GJ, Guo J., Promdet P., Heale FL, Carmalt CJ, Parkin IP Fabrication of robust superhydrophobic surfaces via aerosol-assisted CVD and thermo-triggered healing of superhydrophobicity by recovery of roughness structures[J]. Journal of Materials Chemistry A, 2019, 7(29): 17604-17612” describes the fabrication of self-healing superhydrophobic surfaces using chemical vapor deposition (CVD) of PDMS and epoxy resin polymer films. When the superhydrophobic surface is damaged by sandpaper, the micro-roughness structure is destroyed, and the hydrophobicity is lost. However, upon heating, the epoxy resin polymer chains become active, restoring the original structure and superhydrophobic properties.

[0005] Polydimethylsiloxane (PDMS) polymers are widely used as adhesives due to their excellent mechanical properties, such as abrasion resistance, washability, and good chemical stability. Their good water repellency provides a high contact angle to the substrate, and their high adhesion makes them suitable for use. Environmentally, PDMS is non-toxic, superior to fluorinated compounds, and harmless to the environment and human body. Furthermore, PDMS's transparency and flexibility have led to its widespread application in soft lithography for the fabrication of microfluidic devices. Dual-scale nanoparticles exhibit better cross-linking effects than single-scale nanoparticles, with wetting behavior shifting from a Wenzel state to a Cassie-Baxter state. In this state, droplets are positioned at the peak of surface characteristics, resulting in superior waterproofing.

[0006] The literature “Liu X., Chen JL, Gu LX, Nguyen LT, Cao JQ, Liu HL, Du ZQ, Yu WDA superhydrophobic and flame-retardant cotton fabric fabricated by aneco-friendly assembling method[J]. Textile Research Journal, 2022, 92(15-16):2873-2885” prepared superhydrophobic and flame-retardant cotton fabric using a stepwise soaking and spraying method. First, flame-retardant ethoxysilane-terminated phosphate polyurethane was soaked into a substrate. Then, a mixed solution of methyltriethoxysilane, silica particles, and polydimethylsiloxane was sprayed onto the substrate to obtain the superhydrophobic and flame-retardant cotton fabric. This method of obtaining a superhydrophobic surface through multiple steps increases the complexity of the process. The literature “Xue FX, Shi XT, Bai WX, Li JE, Li YW, Zhu SY, Liu Y.H., Feng LB Enhanced durability and versatile superhydrophobiccoatings via facile onestep spraying technique[J]. Colloids and Surfaces a-Physicochemical and Engineering Aspects, 2022, 640” describes the fabrication of superhydrophobic surfaces by fixing a mixture of silica particles and an inorganic aluminum phosphate (AP) binder onto textiles using a spraying method. However, the fabrication process requires repeated spraying and heat treatment three times. Summary of the Invention

[0007] The main technical problem to be solved by this invention is to provide a self-healing superhydrophobic cotton fabric to address the durability issue.

[0008] The secondary technical problem to be solved by the present invention is to provide a method for preparing a self-healing superhydrophobic cotton fabric, which is simple to prepare, shortens the self-healing time, and simplifies the conditions.

[0009] To address the main technical problems, the technical solution adopted by the present invention is as follows: a self-healing superhydrophobic cotton fabric, comprising a cotton fabric matrix, wherein the cotton fabric matrix contains dispersed micron- and nano-sized silica particles and polydimethylsiloxane, and the mass ratio of the micron- and nano-sized silica particles is 1:1.

[0010] Furthermore, the micron-sized silica particles in step two above have a particle size of 1–10 μm, and the nano-sized silica particles have a particle size of 10–20 nm.

[0011] Furthermore, in step two above, the polydimethylsiloxane is hydroxyl-terminated and has a molecular weight of 50,000.

[0012] To address the secondary issues, the technical solution adopted by this invention is: a method for preparing a self-healing superhydrophobic cotton fabric, comprising the following steps:

[0013] Step 1: Wash cotton fabrics with anhydrous ethanol and deionized water in sequence, and dry them in a drying oven at 60-80℃ for 30 minutes.

[0014] Step 2: Disperse micron-sized silica particles, nano-sized silica particles, polydimethylsiloxane and its curing agent in anhydrous ethanol by magnetic stirring to form solution A;

[0015] Step 3: Place the cotton fabric in solution A and ultrasonically impregnate it. Finally, dry it at 60-80℃ to obtain a self-healing superhydrophobic cotton fabric.

[0016] Furthermore, the aforementioned micron-sized and nano-sized silica particles need to be magnetically stirred in anhydrous ethanol for 90–120 minutes.

[0017] Furthermore, in step three above, the time for ultrasonically immersing the cotton fabric in solution A is 15–30 minutes.

[0018] Furthermore, the curing agent for the aforementioned polydimethylsiloxane is a silane coupling agent, model KH-550.

[0019] Furthermore, the mixing ratio of the above-mentioned polydimethylsiloxane to the curing agent is 10:1.

[0020] The beneficial effects of this invention: Compared with the prior art, this invention provides a biomimetic non-uniform wettability surface with water collection, which has at least the following technical advantages:

[0021] 1) This invention utilizes micron- and nano-scale dual-scale silica particles to construct a unique layered rough structure. When mixed with polydimethylsiloxane, the wettability is higher than that of single-scale silica particles. By fixing the micron- and nano-scale particles inside the cotton fabric using a silane coupling agent (curing agent), the mechanical stability and durability of the superhydrophobic cotton fabric are improved.

[0022] 2) The prepared superhydrophobic cotton fabric has a self-healing function. After the superhydrophobic surface is worn and damaged, reducing its superhydrophobicity, it can be repaired by heating at 80-120℃ for 15-30 minutes. The micro-nano structure and low surface energy of the superhydrophobic surface are also repaired.

[0023] 3) The prepared self-healing superhydrophobic cotton fabric has excellent self-cleaning properties and has potential applications in various fields, such as antibacterial and anti-icing.

[0024] 4) The preparation method of superhydrophobic cotton fabric is simple and time-saving. It uses fluorine-free, low surface energy materials, which have the advantages of being environmentally friendly and non-toxic. Superhydrophobic surfaces are one step closer to industrial production.

[0025] 5) This invention only requires ultrasonically immersing the prepared superhydrophobic solution onto the substrate to complete the preparation, saving multiple steps, time, and costs. The cotton fibers of the cotton fabric provide attachment points for the grafting of micro / nanoparticles. The cured PDMS acts not only as a low surface energy material but also as an adhesive to tightly bond the micro / nanoparticles to the cotton fibers. The dual-scale particles exhibit more complete cross-linking, with a roughness far exceeding that of single-scale particles, and are optimal at a 1:1 ratio, achieving self-healing superhydrophobicity. The successful combination of dual-roughness silica particles, coupled with low surface energy modification, endows the cotton fabric with superhydrophobicity. Using our method, this superhydrophobic cotton fabric exhibits strong mechanical durability under sandpaper abrasion and hand kneading. Even after wear and damage, it can regain its superhydrophobicity after drying at 80°C or above for 30 minutes. In addition to self-healing, the Si2O / PDMS cotton fabric also possesses excellent self-cleaning and anti-corrosion properties. This superhydrophobic cotton fabric has advantages such as simplicity, low cost, and environmental friendliness, and has promising application prospects in the medical, chemical, and infrastructure fields. Attached Figure Description

[0026] Figure 1 Flowchart for the preparation of superhydrophobic cotton fabric;

[0027] Figure 2 SEM images, elemental distribution maps, and XPS spectra of the prepared superhydrophobic cotton fabrics; where (a) and (b) are SEM images of the original cotton fabric and the superhydrophobic cotton fabric, respectively; (c) is the elemental distribution map of the superhydrophobic SiO2 / PDMS cotton fabric; and (d) is the XPS spectra of the pure cotton fabric and the SiO2 / PDMS cotton fabric.

[0028] Figure 3Contact angle curves, SEM images, and simplified wetting models of the prepared superhydrophobic cotton fabrics are shown. Among them, (a) CA (μ:n = 1:0, 2:1, 1:1, 1:2, and 0:1) of coatings with different mass ratios of micron / nano SiO2 particles; (be) SEM images of coatings with different mass ratios of micron / nano SiO2 particles ((b) μ:n = 1:0, (c) μ:n = 2:1, (d) μ:n = 1:2, (e) μ:n = 0:1); (f) Simplified wetting model of the rough structure of the microstructure; (g) Simplified wetting model of the rough structure of the nanostructure; (h) Simplified wetting model of the rough structure of the micro-nano hierarchical structure.

[0029] Figure 4 Schematic diagram of mechanical wear test, curve of CA change of cotton fabric with period increase, and sweeping

[0030] Scanning electron microscopy, droplet contact angle at pH value, and contact angle of cotton fabric after 90 days; where, (a) schematic diagram of mechanical wear test, (b) evolution of CA of SiO2 / PDMS cotton fabric with increasing wear cycle; (c)-(d) SEM observation of sandpaper wear cycle of SiO2 / PDMS cotton fabric before and after 30 days; (e) droplet contact angle at different pH values; (f) and (g) contact angle of SiO2 / PDMS cotton fabric before and after 90 days.

[0031] Figure 5 middle, Figure 5 (a) Contact angle of SiO2 / PDMS cotton fabric after abrasion following heating at different temperatures for 2 min; (b) Changes in water contact angle during each abrasion heating process; (c) SEM image of SiO2 / PDMS cotton fabric after abrasion; (d) SEM image of SiO2 / PDMS cotton fabric after healing; (e) EDS and MAP scans of a single cotton fiber in its original state; (f) EDS and MAP scans of a single cotton fiber damaged by sandpaper 30 times; (g) EDS and MAP scans of a single cotton fiber after self-healing; (h) Map scan results of changes in C, O, and Si element content of SiO2 / PDMS cotton fabric in its original state, after abrasion, and after the self-repair process; (i) Broad XPS spectra of SiO2 / PDMS cotton fabric before abrasion, after abrasion, and after heat treatment.

[0032] Figure 6 In the middle, (a) the working mechanism of the intelligent self-healing process of SiO2 / PDMS cotton fabric; (b)-(f) the self-healing of SiO2 / PDMS superhydrophobic cotton fabric after immersion in solutions of different pH values.

[0033] Figure 7In the image, (a) shows the self-cleaning process of ordinary cotton fabrics, (b)-(c) show the self-cleaning process of SiO2 / PDMS cotton fabrics under different conditions, and (d) shows photographs of various droplets on SiO2 / PDMS cotton fabrics. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] Example 1: A self-healing superhydrophobic cotton fabric, comprising a cotton fabric matrix, wherein the cotton fabric matrix contains dispersed micron-sized silica particles, nano-sized silica particles, and polydimethylsiloxane, the micron-sized silica particles and nano-sized silica particles are mixed in a 1:1 ratio, the polydimethylsiloxane is hydroxyl-terminated with a molecular weight of 50,000, the micron-sized silica particles have a particle size of 1-10 μm, and the nano-sized silica particles have a particle size of 10-20 nm; the preparation method of the self-healing superhydrophobic cotton fabric includes the following steps:

[0036] S1. Wash cotton fabrics with anhydrous ethanol and deionized water in sequence, and dry them in a drying oven at 60-80℃ for 15-30 minutes.

[0037] S2. Disperse micron-sized and nano-sized silica particles with polydimethylsiloxane and its curing agent in anhydrous ethanol by magnetic stirring to form solution A, and stir magnetically for 90-120 min; the curing agent for polydimethylsiloxane is a silane coupling agent, model KH-550; the mixing ratio of polydimethylsiloxane to curing agent is 10:1;

[0038] S3. Place the cotton fabric in solution A and ultrasonically immerse it for 15-30 minutes. Finally, dry it at 60-80℃ to obtain a self-healing superhydrophobic cotton fabric.

[0039] Comparative Example 2: A cotton fabric comprising a cotton fabric matrix, wherein the cotton fabric matrix contains dispersed micron-sized silica particles, nano-sized silica particles, and polydimethylsiloxane, wherein the mixing ratio of micron-sized silica particles to nano-sized silica particles is 2:1, the polydimethylsiloxane is hydroxyl-terminated with a molecular weight of 50,000, the micron-sized silica particles have a particle size of 1–10 μm, and the nano-sized silica particles have a particle size of 10–20 nm; the preparation method of the self-healing superhydrophobic cotton fabric includes the following steps:

[0040] S1. Wash cotton fabrics with anhydrous ethanol and deionized water in sequence, and dry them in a drying oven at 60-80℃ for 15-30 minutes.

[0041] S2. Disperse micron-sized and nano-sized silica particles with polydimethylsiloxane and its curing agent in anhydrous ethanol by magnetic stirring to form solution A, and stir magnetically for 90-120 min; the curing agent for polydimethylsiloxane is a silane coupling agent, model KH-550; the mixing ratio of polydimethylsiloxane to curing agent is 10:1;

[0042] S3. Place the cotton fabric in solution A and ultrasonically immerse it for 15-30 minutes. Finally, dry it at 60-80℃ to obtain a cotton fabric.

[0043] Comparative Example 3: A cotton fabric, comprising a cotton fabric matrix, wherein the cotton fabric matrix contains dispersed micron-sized silica particles, nano-sized silica particles, and polydimethylsiloxane, the mixing ratio of micron-sized silica particles to nano-sized silica particles is 1:2, the polydimethylsiloxane is hydroxyl-terminated with a molecular weight of 50,000, the micron-sized silica particles have a particle size of 1–10 μm, and the nano-sized silica particles have a particle size of 10–20 nm; the preparation method of the cotton fabric includes the following steps:

[0044] S1. Wash cotton fabrics with anhydrous ethanol and deionized water in sequence, and dry them in a drying oven at 60-80℃ for 15-30 minutes.

[0045] S2. Disperse micron-sized and nano-sized silica particles with polydimethylsiloxane and its curing agent in anhydrous ethanol by magnetic stirring to form solution A, and stir magnetically for 90-120 min; the curing agent for polydimethylsiloxane is a silane coupling agent, model KH-550; the mixing ratio of polydimethylsiloxane to curing agent is 10:1;

[0046] S3. Place the cotton fabric in solution A and ultrasonically immerse it for 15-30 minutes. Finally, dry it at 60-80℃ to obtain a cotton fabric.

[0047] Comparative Example 4: A cotton fabric comprising a cotton fabric matrix, wherein the cotton fabric matrix contains dispersed micron-sized silica particles, nano-sized silica particles, and polydimethylsiloxane, wherein the mixing ratio of micron-sized silica particles to nano-sized silica particles is 1:0, the polydimethylsiloxane is hydroxyl-terminated with a molecular weight of 50,000, and the micron-sized silica particles have a particle size of 1–10 μm; the preparation method of the cotton fabric includes the following steps:

[0048] S1. Wash cotton fabrics with anhydrous ethanol and deionized water in sequence, and dry them in a drying oven at 60-80℃ for 15-30 minutes.

[0049] S2. Disperse micron-sized and nano-sized silica particles with polydimethylsiloxane and its curing agent in anhydrous ethanol by magnetic stirring to form solution A, and stir magnetically for 90-120 min; the curing agent for polydimethylsiloxane is a silane coupling agent, model KH-550; the mixing ratio of polydimethylsiloxane to curing agent is 10:1;

[0050] S3. Place the cotton fabric in solution A and ultrasonically immerse it for 15-30 minutes. Finally, dry it at 60-80℃ to obtain a cotton fabric.

[0051] Comparative Example 5: A cotton fabric comprising a cotton fabric matrix, wherein the cotton fabric matrix contains dispersed micron-sized silica particles, nano-sized silica particles, and polydimethylsiloxane, the mixing ratio of micron-sized silica particles to nano-sized silica particles is 0:1, the polydimethylsiloxane is hydroxyl-terminated with a molecular weight of 50,000, and the nano-sized silica particles have a particle size of 10-20 nm; the preparation method of the cotton fabric includes the following steps:

[0052] S1. Wash cotton fabrics with anhydrous ethanol and deionized water in sequence, and dry them in a drying oven at 60-80℃ for 15-30 minutes.

[0053] S2. Disperse micron-sized and nano-sized silica particles with polydimethylsiloxane and its curing agent in anhydrous ethanol by magnetic stirring to form solution A, and stir magnetically for 90-120 min; the curing agent for polydimethylsiloxane is a silane coupling agent, model KH-550; the mixing ratio of polydimethylsiloxane to curing agent is 10:1;

[0054] S3. Place the cotton fabric in solution A and ultrasonically immerse it for 15-30 minutes. Finally, dry it at 60-80℃ to obtain a cotton fabric.

[0055] The contact angle of the self-healing superhydrophobic cotton fabric prepared with a mixing ratio of micron-sized and nano-sized silica particles of 1:1 was tested three times, and the results of three tests at other ratios are shown in Table 1.

[0056] Table 1. Contact angles of three tests at different ratios

[0057]

[0058] To illustrate the effects of the present invention, the following experiment was conducted:

[0059] Experimental Section

[0060] 1. Raw materials: Anhydrous ethanol and methylene blue were purchased from Guizhou Boao Ruijie Biotechnology Co., Ltd.; SiO2 (1μm, 99%, spherical) and SiO2 (20nm, 99%, spherical) were purchased from Hebei Bocheng Metallurgical Research Center; PDMS (PDMSSYLGARD184) and its curing agent were purchased from Dow Corning; cotton textile fabric was purchased from Hongda Textile Factory.

[0061] 2. Preparation of SiO2 / PDMS self-healing superhydrophobic cotton fabric

[0062] First, 0.45g μ-SiO2, 0.45g n-SiO2, 0.3g PDMS, and 0.03g PDMS curing agent (10:1) were mixed into 30ml anhydrous ethanol. Second, the mixture was magnetically stirred for 2 hours, and then the fabric was immersed in the stirred mixture (enough to cover the fabric) and ultrasonically soaked for 30 minutes. Finally, the fabric was cured in a 60℃ drying oven for 30 minutes to obtain a SiO2 / PDMS self-healing superhydrophobic cotton fabric. Note that to ensure the mixture fully penetrates the fabric, it needs to be washed with ethanol and deionized water and dried in a 60℃ drying oven for 30 minutes. The above preparation process is as follows: Figure 1 As shown.

[0063] 3. Characterization and Analysis

[0064] The surface morphology and repair status of the prepared SiO2 / PDMS coating were characterized using a Hitachi FlexSEM1000 scanning electron microscope (SEM). The samples were sputter-coated with gold before testing. The wettability of the coating was characterized using a Kruss DSA100 contact angle meter (DSA100), with a droplet volume of 5 μL, and six measurements were taken and the average value calculated. The chemical composition of the coating surface was determined using energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). All optical photographs and videos were obtained using a smartphone.

[0065] 4. Mechanical wear resistance test

[0066] Mechanical durability testing of the SiO2 / PDMS superhydrophobic surface was conducted using abrasive paper. The sample was placed on abrasive paper (P1000 grade), with one side of the superhydrophobic surface in contact with the paper. A 200g weight was placed in the center of the sample, and the sample was moved 20 cm on the abrasive paper by an external force parallel to the substrate, with the speed controlled at 3-4 cm / s. During the abrasion test, the abrasion coefficient (CA) of the sample was measured every 20 cm.

[0067] 5. Chemical stability test

[0068] The superhydrophobic surface was immersed in strong acid and strong base solutions (pH values ​​1, 2, 13, and 14) for 1 hour, and the contact angle (CA) was recorded. The contact angle of the superhydrophobic surface was tested by droplets of strong acid and strong base (pH values ​​1, 2, 13, and 14) and physiological saline (pH value 7, 0.9% NaCl solution) to detect the chemical stability of the superhydrophobic surface.

[0069] 6. Self-healing properties

[0070] The chemical stability (CA) of superhydrophobic surfaces after 30 cycles of sanding was measured. These surfaces were then heated in drying ovens at 60℃, 80℃, 100℃, 120℃, 140℃, and 160℃, and the CA after heating was recorded to study their self-healing properties. The same method was used to investigate chemical stability; superhydrophobic surfaces that had failed after being immersed in strong acids and alkalis for 1 hour were placed in a drying oven and heated to study their self-healing properties.

[0071] Results and Discussion

[0072] 1. SiO2 / PDMS self-healing superhydrophobic cotton fabric

[0073] The morphology of ordinary cotton fabric and the obtained SiO2 / PDMS superhydrophobic cotton fabric was characterized by scanning electron microscopy (SEM). Figure 2 a. Ordinary cotton fabric has smooth cotton fibers with no rough structure. In contrast, in... Figure 2 In step b, the cotton fibers are covered with micro- and nano-particles, which are evenly distributed throughout the entire fiber. This was obtained using energy-dispersive scanning spectroscopy (EDS). Figure 2 The results show that the main elements on the SiO2 / PDMS superhydrophobic cotton fabric are C, O, and Si, and the distribution diagram shows that they are uniformly distributed on the surface. Besides EDS, Figure 2 X-ray photoelectron spectroscopy (XPS) revealed new representative peaks for Si2p and Si2s in the SiO2 / PDMS cotton fabric at 100–200 eV. This indicates that PDMS and SiO2 were successfully grafted onto the cotton fabric, and the elemental distribution was consistent with the desired results. Figure 1 According to Brownian motion, when particles of different sizes are mixed, the direction of particle movement follows the concentration gradient generated by solvent evaporation. As we know, PDMS and EP are the most commonly used polymer materials for preparing superhydrophobic surfaces, and are usually used as adhesives to bond the substrate and coating together, improving the mechanical durability of the superhydrophobic surface. Here, in addition to acting as an adhesive to firmly bond the particles to the substrate, PDMS itself, as a low surface energy, is also stored in the cotton fibers.

[0074] It is hypothesized that the layered rough structure caused by these dual-scale nanoparticles is a key factor in the formation of the superhydrophobic surface, ensuring low contact area and permeability of droplets on the surface. To further confirm this, in the experimental section, keeping the total number of particles constant, the particles were replaced with 0.9 g of μ-SiO2 or 0.9 g of n-Si2 to obtain coatings with a single roughness on cotton textiles. In addition, dual-roughness superhydrophobic coatings with different specific gravities of nano- or micro-particles were also prepared with the total amount constant. Figure 3 In group a, the contact angle of micro / nano silica with different mass ratios is the largest at a 1:1 ratio, reaching 155.4°. When only micron-sized particles are present (μ:n = 1:0), Figure 3 b) Micrometer-sized particles are relatively large and difficult to adhere to fibers via PDMS. Locations where adhesion fails are simply low surface energy, insufficient to constitute superhydrophobicity. However, with only nano-sized particles, due to their small size and high mobility, numerous spherical structures formed by the self-assembly of n-SiO2 can be observed, exhibiting excellent adhesion to the fibers. However, the dense aggregation of these spherical particles increases the contact area between water droplets and the surface, preventing the trapping of more air layers. Considering the interaction forces between the two types of particles and their different mobility and dispersion, the cross-linking effect produced during mixing is higher than that of single roughness, thus a micro / nano particle hybrid structure was prepared. When nano-sized particles outnumber micrometer-sized particles (μ:n = 1:2), Figure 3 d) Unlike nanoscale particles, micron-sized particles can also cross-link and adhere to the fiber in small quantities. However, the roughness is still insufficient, resulting in an excessively large contact area. Finally, an attempt was made to use more micron-sized particles than nanoscale particles. (μ:n = 2:1, Figure 3 e) Some μ-SiO2 particles are cross-linked onto the fiber, while some n-SiO2 particles are first cross-linked with the μ-SiO2 particles. The inter-particle interaction forces cause them to adhere together onto the fiber. This illustrates the role of nanostructures in modulating solid-liquid interactions on superhydrophobic surfaces. Another attempt involves more micron-sized particles (μ:n = 2:1) than nanoscale particles. Figure 3 c). However, due to the excessive number of μ-SiO2 particles, some fibers still failed to attach successfully, resulting in contact angles below 150°.

[0075] Simplified schematic diagrams of three roughness structures on the surface of SiO2 / PDMS cotton textiles were created based on the Wenzel and Cassie-Baxster wetting model. Figure 3 f, 3g, and 3h).

[0076] 2. Stability of SiO2 / PDMS self-healing superhydrophobic cotton fabric

[0077] Based on the practical applications and major challenges of superhydrophobic surfaces, those prepared using nanoparticles and chemical methods exhibit poor mechanical stability and are easily damaged. Therefore, testing the mechanical robustness of superhydrophobic surfaces is essential. Mechanical wear and chemical stability tests were conducted on SiO2 / PDMS superhydrophobic cotton fabrics.

[0078] The first step is mechanical wear testing, which typically involves rubbing the substrate with sandpaper and weights. Figure 4 Figure a shows a schematic diagram of a mechanical wear test on a superhydrophobic textile under a certain load (200g, 1000 mesh). As the wear cycle increases, the contact angle CA gradually decreases. After 30 wear cycles (…),… Figure 4 After b), the contact angle decreased from 155.4° to 141.6°. Although the water droplets on the superhydrophobic cotton fabric still maintained a spherical shape, the roll-off angle increased significantly. After the fabric was flipped 180°, the water droplets stuck to the fabric and did not fall off unless force was applied. This is because abrasion disrupted the rough structure of the superhydrophobic surface, resulting in a surface morphology as shown in [the image / description]. Figure 4 c-4d. After wear, the micro- and nano-particles on the fiber decreased significantly, presumably falling off during the friction process with the weights. The coating thinned, but some residue remained, accompanied by particle accumulation. In addition, the exposed parts maintained good hydrophobicity due to the low surface energy provided by PDMS stored inside the fiber.

[0079] It is worth mentioning that, compared with the superhydrophobic preparations reported in recent years, the superhydrophobic coating of this patent has superior mechanical wear resistance. The literature "Chen BY, Zhang RR, Fu HX, Xu JD, Jing Y., Xu G.H., Wang B., Hou X. Efficient oil-water separation coating with robust superhydrophobicity and high transparency[J]. Scientific Reports, 2022, 12(1)" successfully deposited carbon nanoparticles of candle soot on a substrate using vapor deposition to increase roughness. However, this method could only withstand 20 cycles of wear on 1200-grit sandpaper under a 100g load (10cm per cycle). The contact angle fluctuated with the number of wear cycles, falling below 150° several times, indicating instability. The literature “DMRagheb, AMAbdel-Gaber, FMMahgoub, MEMohamed. Eco-friendly method for construction of superhydrophobic graphene-based coating on copper substrate and its corrosion resistance performance[J]. Scientific Reports, 2022, 12(1). 25” describes the electrostatic deposition of Ni, Ni-graphene, Ni-G, and films onto a copper substrate, followed by modification of the coating with myristic acid (MA) to obtain a superhydrophobic copper surface. However, this coating can only withstand wear of 600 mm under a weight of 1.5 kPa. Therefore, the SiO2 / PDMS superhydrophobic cotton fabric we prepared exhibits superior mechanical robustness. Even after 30 wear cycles, the hydrophobicity remains.

[0080] In addition to immersion, the contact angles of acid and alkali solutions were also measured when they were directly dripped onto SiO2 / PDMS cotton fabric. Figure 5 e. Droplets at different pH values ​​(1, 2, 7, 13, and 14) maintained contact angles exceeding 150° on the SiO2 / PDMS cotton fabric. (The solution at pH 7 was prepared with 0.9% NaCl, equivalent to physiological saline concentration.) We also found that the prepared SiO2 / PDMS cotton fabric remained superhydrophobic after 50 days of storage at room temperature, with a contact angle of 152.4°, demonstrating extremely strong stability.

[0081] 3. Self-healing properties

[0082] The prepared cotton fabric is damaged by physical friction during use. As mentioned earlier, the contact angle of the SiO2 / PDMS cotton fabric decreased from 155.4° to 141.6° after 30 cycles of sandpaper friction. However, after heating the damaged cotton fabric in drying ovens at different temperatures for 30 minutes, the contact angle recovered to over 150° at 120°C. Figure 5 a) It can also be restored at 140℃. Cotton fabric cannot be restored at 160℃, and the edges of the cotton fabric show scorching marks, with a brown surface. Therefore, a drying temperature of 120℃ was selected, and an abrasion repair cycle experiment was conducted on the SiO2 / PDMS cotton fabric. Figure 5 b. Even after 8 wear repairs, it still achieves a superhydrophobic effect, with water droplets remaining on the superhydrophobic cotton fabric without penetration. Furthermore, initially, after 30 wears, water droplets did not fall off when flipped, but after heat repair, they easily roll off, with a significantly reduced roll-off angle. This demonstrates excellent self-healing performance.

[0083] To investigate the mechanism of self-repair, we compared the morphological images of the worn and repaired parts. Figure 7 (cd). It is evident that micro- and nano-particles have re-aggregated on the repaired fibers, forming a layered, rough structure. This is because during the wear process, the accumulated particles, after heating, self-diffused to areas where they were not attached. It is known that SiO2 particles undergo intense self-diffusion under heating. Due to the reduction in particle size during wear, the number of accumulated particles is limited, and the diffused particles cannot completely cover the fiber, leaving gaps. Simultaneously, it is observed that the blocky structures formed by μ-SiO2 particles are more numerous than those formed by spherical n-SiO2 particles, indicating that spherical n-SiO2 particles are more easily worn away during friction. This morphological healing phenomenon is termed the first mechanism of SiO2 self-healing. Furthermore, the second mechanism of SiO2 / PDMS intelligent self-repair was verified using EDS surface scanning and XPS spectroscopy. During ultrasonic immersion, a large amount of PDMS polymer penetrated into the amorphous regions of the cellulose macromolecules, and after drying, the PDMS was preserved within the cotton fibers. After mechanical wear damages the surface, the removal of PDMS distributed between the μ / n-SiO2 particles and the substrate leads to a decrease in surface superhydrophobicity and an increase in surface free energy. However, after heating, the PDMS polymer groups stored in the cotton fibers migrate from the interior to the surface due to their high mobility, providing low surface energy. For example... Figure 5 e and h, the C, O, and Si element contents of the superhydrophobic cotton fabric are 18.04%, 18.57%, and 65.37%, respectively. After wear, the Si element content decreases to Figure 5 The Si content increased from 42.84% at f and 5h, while the O content increased to 20.77%, indicating that the top-layer PDMS was destroyed and the μ / n-SiO2 particles were worn away. After heating, the Si content increased to 57.41%. Figure 5The results (g and 5h) closely approximate the state of superhydrophobic cotton fabric, verifying that the PDMS polymer preserved in the cotton fibers successfully migrated to the outer surface of the cotton fabric. To further confirm this, XPS spectral analysis was also performed on the superhydrophobic cotton fabric, the worn cotton fabric, and the healed cotton fabric. Figure 5 The representative peak of Si 2p at 101.0 eV weakens after wear but strengthens again after heat healing. This result is consistent with the EDS results obtained by surface scanning, proving that the wear and healing process is a process of decreasing and increasing Si. Therefore, the self-healing process of SiO2 / PDMS textiles mainly relies on morphological healing and the migration of PDMS elements.

[0084] The entire healing mechanism and process can be derived from Figure 6 The mechanism diagram shown in Figure a illustrates this process. After wear, micro / nano particles fall off or accumulate on the fiber due to repeated abrasion. Simultaneously, the surface PDMS content decreases, leading to a reduced contact angle. The accumulated particles diffuse upon heating and migrate to the top layer along with the PDMS within the cotton fiber, resulting in a low surface energy, micro-rough structure. After immersing the superhydrophobic cotton fabric in strong acid and alkali solutions (pH = 1, 2, 13, and 14) for 1 hour, the contact angle decreases, and the superhydrophobicity is lost. However, after heating at 80°C for 30 minutes, it self-heals, and the contact angle returns to above 150°. Figure 6 However, when immersed in a neutral environment (0.9% NaCl solution), the superhydrophobicity was not destroyed after 1 hour. Figure 6 f)

[0085] In existing studies, the wear repair mechanism is a single repair of microstructure or repair of elemental composition. The literature "MZGe,CYCao,FHLiang,R.Liu,Y.Zhang,W.Zhang,TXZhu,B.Yi,YXTang,Y.4K.Lai.A"PDMS-in-water"emulsion enables mechanochemically robust superhydrophobic 5surfaces with self-healing nature[J].Nanoscale Horizons,2020,5(1):65-73" prepared self-healing superhydrophobic cotton fabric by dissolving PDMS in water to form a dispersion. In their self-healing mechanism, there is no change in microstructure, only the internal elemental composition changes. The literature “Wang YK, Liu YP, Li J., Chen LW, Huang SL, Tian XL Fast selfhealing superhydrophobic surfaces enabled by biomimetic wax regeneration[J]. Chemical Engineering Journal, 2020, 390” reports a unique self-healing superhydrophobic poly(dimethylsiloxane) / n-nonadenine wax composite surface, whose self-healing function is due to the migration of wax components after damage, restoring the microstructure. Unlike their work, where PDMS did not play a major repair role (PDMS was confined to the cross-linked network), the microstructure formed by wax migration was the primary factor. In the self-healing mechanism of this patent, PDMS can migrate within the fibers, and the microstructure is also repaired. This patent combines dual repair of microstructure and chemical components, achieving self-healing when a single element cannot repair the damage, relying on microstructure repair. This provides more insights for future theories of self-healing mechanisms.

[0086] 4. Self-cleaning and anti-fouling properties

[0087] In addition to mechanical and chemical stability, the stain resistance and self-cleaning properties of SiO2 / PDMS cotton fabrics were also tested. To demonstrate the self-cleaning property of SiO2 / PDMS cotton fabrics, ordinary cotton fabrics were compared with SiO2 / PDMS cotton fabrics. Chalk dust was used as the contaminant, and methylene blue aqueous solution was used as the cleaning agent to clean the cotton fabrics. Figure 7In cases a and 7b, when methylene blue solution was dropped onto ordinary cotton fabric, the fabric was directly wetted, while the chalk dust remained in place. Conversely, when methylene blue was dropped onto SiO2 / PDMS cotton fabric, the solution formed spherical droplets that rolled off, carrying away the chalk dust. After multiple drops, all the chalk dust was eventually removed, achieving a self-cleaning function. To demonstrate the stain-resistant properties of the SiO2 / PDMS cotton fabric, it was immersed in a methylene blue solution. Figure 7 c. After being immersed in a methylene blue aqueous solution, the SiO2 / PDMS cotton fabric remained dry. In addition, various solutions, such as coffee, milk, tea, and blood, were also applied to the SiO2 / PDMS cotton fabric. Figure 7 As shown in Figure d, these solutions can all remain on the cotton fabric in a spherical shape without wetting it. This demonstrates that the SiO2 / PDMS cotton fabric has good self-cleaning and stain-resistant properties.

[0088] in conclusion

[0089] In summary, a simple one-step immersion method based on two scales was developed, and a mechanochemically robust superhydrophobic SiO2 / PDMS cotton fabric was designed. The combination of two-scale silica particles and PDMS provides the cotton fabric with a layered, rough structure and low surface energy, resulting in a water contact angle greater than 155°. Due to the unique adhesive strength of PDMS, the prepared coating exhibits excellent mechanical durability and chemical stability. Even after 3 hours of exposure to various mechanical abrasions (e.g., 30 sandpaper abrasion cycles) and harsh environments (e.g., chemical corrosion with pH=1, pH=2, and 3.5 wt% sodium chloride, pH=13, pH=14), the coating still maintains its extreme water resistance. In particular, it is able to restore its superhydrophobicity despite being subjected to more than 30 abrasion cycles. This intelligent self-healing property, driven by the self-diffusion process of the micro / nanoparticles and PDMS polymer, allows it to recover its superhydrophobicity after abrasion and corrosion. This self-healing property has been tested to be repeatable at least 8 times. Thanks to its inherent design, the superhydrophobic SiO2 / PDMS cotton fabric has potential applications in various fields, such as anti-icing and antibacterial properties.

[0090] Scanning electron microscopy (SEM) images of the fabricated superhydrophobic cotton revealed that the fibers were covered with micro- and nano-sized silica particles, making the smooth cotton fibers rough. This micro- and nano-roughened structure, along with the low surface energy of polydimethylsiloxane, is key to the superhydrophobicity of the cotton fabric.

[0091] The superhydrophobic cotton fabric prepared by this method possesses self-healing capabilities, and its self-healing function and mechanism were investigated. The mechanical wear self-healing function of the superhydrophobic cotton fabric was studied using a sandpaper abrasion test. SEM images of the microstructure of the superhydrophobic cotton fabric after 30 abrasion cycles showed that after abrasion, micron- and nano-sized silica particles on the surface of the fabric were either worn away or accumulated on the cotton fibers under the pushing force of weights. The exposed PDMS polymer inside the fibers was also damaged by abrasion, leading to an increase in surface energy. After heating in a drying oven, the PDMS polymer groups stored in the cotton fibers migrated from the interior to the surface due to their high mobility, providing low surface energy. Simultaneously, the PDMS migration promoted the redispersion of aggregated particles on the fibers.

[0092] Based on the wear and tear healing process and self-healing mechanism diagram of superhydrophobic cotton fabric, the main reasons for the self-healing function of the superhydrophobic cotton fabric prepared by this method are twofold: the migration of particles and PDMS polymer after heating.

[0093] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A self-healing superhydrophobic cotton fabric, comprising a cotton fabric matrix, characterized in that: The cotton fabric matrix is ​​dispersed and impregnated with micron-sized silica particles, nano-sized silica particles, and polydimethylsiloxane; the mass ratio of micron-sized silica to nano-sized silica particles is 1:1, the micron-sized silica particles have a particle size of 1-10 μm, and the nano-sized silica particles have a particle size of 10-20 nm; the polydimethylsiloxane is hydroxyl-terminated and has a molecular weight of 50,000; the curing agent for the polydimethylsiloxane is a silane coupling agent, model KH-550; the mixing ratio of polydimethylsiloxane to curing agent is 10:

1. The dispersion and impregnation method is as follows: the micron-sized silica particles, nano-sized silica particles, polydimethylsiloxane, and their curing agent are dispersed in anhydrous ethanol by magnetic stirring to form solution A; the cotton fabric is placed in solution A and ultrasonically impregnated.

2. The method for preparing a self-healing superhydrophobic cotton fabric according to claim 1, characterized in that: Includes the following steps: Step 1: Wash cotton fabrics with anhydrous ethanol and deionized water in sequence, and dry them in a drying oven at 60-80℃ for 30 minutes. Step 2: Disperse micron-sized silica particles, nano-sized silica particles, polydimethylsiloxane and its curing agent in anhydrous ethanol by magnetic stirring to form solution A; Step 3: Place the cotton fabric in solution A and ultrasonically impregnate it. Finally, dry it at 60-80℃ to obtain a self-healing superhydrophobic cotton fabric.

3. The method for preparing a self-healing superhydrophobic cotton fabric according to claim 2, characterized in that: The micron-sized and nano-sized silica particles were magnetically stirred in anhydrous ethanol for 90–120 min.

4. The method for preparing a self-healing superhydrophobic cotton fabric according to claim 2, characterized in that: In step three, the cotton fabric is ultrasonically immersed in solution A for 15 to 30 minutes.

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