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Efficient scald-preventing enabled by robust polyester fabrics with hot water repellency and water impalement resistance
Journal of Colloid and Interface Science 566 (2020) 69–78
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Efficient scald-preventing enabled by robust polyester fabrics with hot water repellency and water impalement resistance Ning Tian a,b, Jinfei Wei a, Yabin Li a, Bucheng Li a, Junping Zhang a,b,⇑ a b
Center of Eco-material and Green Chemistry, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, PR China
g r a p h i c a l a b s t r a c t
a r t i c l e
i n f o
Article history: Received 18 October 2019 Revised 17 January 2020 Accepted 18 January 2020 Available online 20 January 2020 Keywords: Hot water repellency Scald-preventing Superhydrophobic Surface chemistry Silanes
a b s t r a c t Scald is a kind of common injury for human beings caused by contacting with hot liquids and/or vapor. Herein, we report the preparation of an advanced fabric for efficient scald-preventing by dip-coating a common polyester fabric in a hexadecyl polysiloxane (HD-POS) aqueous suspension, which was synthesized via a waterborne and nonfluorinated approach. Thanks to the hierarchical micro-/nanostructure of the fabric, stable bonding of the compact HD-POS layer on the polyester microfibers, and inherent high stability and elasticity of HD-POS, the fabric features excellent hot water repellency even for dynamic boiling water with a high water impalement resistance of up to 5 grades according to the water repellency grade test. In addition, the fabric shows extraordinary mechanical stability, e.g., its superhydrophobicity remained nearly unchanged after 200 cycles washing, 10,000 cycles Martindale abraison or 1000 cycles 100% streching and releasing. It also exhibits superior environmental robustness (117 d outdoor test) and chemical robustness (7 d immersion in 1 M HCl or NaOH solution, 60 min ultrosonication in both water and anchol immersion) in various harsh conditions. By applying as an advanced fabric for efficient scald-preventing, it can avoid direct contact of hot water and vapor with rat skin by preventing penetration of hot water and most of vapor. It could also significantly reduce heat conduction and radiation to rat skin by reducing contact time of hot water with the fabric (decreased 10 s more quickly than the pristine fabric to 60 °C when encountering 100 mL of 92 °C water). As a result, the fabric in contact with the skin keeps dry and the fabric temperature is much lower than that of the pristine fabric once
⇑ Corresponding author at: Center of Eco-material and Green Chemistry, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China. E-mail address: [email protected] (J. Zhang). https://doi.org/10.1016/j.jcis.2020.01.067 0021-9797/Ó 2020 Elsevier Inc. All rights reserved.
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encountering hot water, thus showing great potentials as an advanced fabric for efficient scaldpreventing applications. Ó 2020 Elsevier Inc. All rights reserved.
1. Introduction Scald is a kind of common injury for human beings, especially for children and elderly people, usually caused by contacting with hot liquids and/or vapor [1–3]. More than 110,000 people are treated in hospital because of scalds every year [4]. Usually, scald is not fatal, but may cause intense pain, infection and fester for a long time, and leave scarring and emotional hurt [5]. In the most of scald cases, hot water wets and penetrates through the clothes of victims along with hot vapor, causing scald by heat from the hot water itself and condensation of the vapor [4]. Severity of scald depends on temperature of hot water and vapor, water-skin contact time and contact area, etc. Scald happened in 30 s at 55 °C and in 5 s at 60 °C for adults, and in shorter time and at lower temperature for children because of their thin skin [1,3,6]. This means common clothes would actually aggravate scald severity, as they can be easily wetted and penetrated by hot water and vapor [2]. Therefore, there is an urgent need for developing advanced fabrics to reduce or even prevent wetting and penetration of hot water and vapor and then to avoid or at least alleviate most of scalds. Superhydrophobic fabrics are of great interest because of their high repellency to water [7–11]. Although superhydrophobic fabrics can prevent wetting by room temperature water, their hot water repellency and water impalement resistance are seldom studied. Most of natural and artificial superhydrophobic surfaces lose superhydrophobicity once encountered with hot water, owing to the lower surface tension of hot water and condensation of hot vapor into the micro-/nanostructures [12–14]. Though the employment of superhydrophobic fabrics for scald-preventing applications has been reported [4], few studies involved heat distribution, duration time of hot water or animal scald model test. On the other hand, the assessment of superhydrophobicity now largely depends on the water contact angle (CA), CA hysteresis or sliding angle [15–20], which is acctrually insufficient to evaluate their performance in terms to scald-preventing applications. High water impalement resistance of superhydrophobic surfaces is imperative for many of their applications including airplanes, trains, wind turbine blades and clothes.[21,22] Though great progress in superhydrophobic surfaces has been achieved in the past two decades, only a few examples show hot water repellency or high water impalement resistance [12,21,23,24]. Meanwhile, superhydrophobic fabrics with such merits have not been reported. Safety issues are one of great concerns for preparation of superhydrophobic fabrics, of which fluorinated compounds and organic solvents are frequently used [25–27]. The fluorinated compounds are not degradable and may cause bioaccumulation [28], leading to prohibition in the USA and EU countries [29,30]. In the textile dyeing and finishing industry, almost all processes are waterborne and the use of organic solvents will make a technique impractical because of safety concern [31]. It remains challenging to prepare robust superhydrophobic fabrics via waterborne and nonfluorinated approaches. Poor mechanical durability is a fatal defect of superhydrophobic surfaces [32–34]. The combination of inherent microstructure of fabrics and covalent bonding of coatings onto the fabrics could improve mechanical durability [35–37]. However, the waterborne and/or nonfluorinated superhydrophobic fabrics developed so far could withstand very limited washing and abrasion [38]. Hence, superhydrophobic fabrics that can withstand washing, abrasion,
stretching and outdoor settings are highly desired. Moreover, functional superhydrophobic fabrics with additional features besides self-cleaning are receiving increasing attention to meet diverse applications, e.g., pressure sensors, electromagnetic interference shielding and supercapacitor [39–41]. Here, we report a waterborne and nonfluorinated approach for preparing robust superhydrophobic polyester (PET) fabrics with excellent hot water repellency and water impalement resistance for efficient scald-preventing. First, a hexadecyl polysiloxane (HD-POS) aqueous suspension was prepared by hydrolytic condensation of hexadecyltrimethoxysilane (HDTMS) and (3-glycidyloxy propyl)trimethoxysilane (GPTMS). Then, the superhydrophobic HD-POS@PET fabrics were prepared by dip-coating in the HDPOS aqueous suspension. The superhydrophobic HD-POS@PET fabrics feature (i) excellent hot water repellency even for dynamic boiling water, (ii) high water impalement resistance of 5 grades according to the water repellency grade (WRG) test, and (iii) extraordinary robustness against washing, abrasion, UV irradiation, corrosive liquids erosion and outdoor weathering, etc. Furthermore, the HD-POS@PET fabrics can efficiently prevent scald by hot water, which was proved for the first time by simulated test and rat scald model test. 2. Materials and methods 2.1. Materials The PET fabric was supplied by Bevery, Shanghai China. HDTMS (98%) and GPTMS (98%) were bought from Gelest. HCl (36–38%) and NaOH (99.7%) were bought from China National Medicines Co. Ltd. Sauce, coffe, vinegar and cola were bought from a supermarket in Lanzhou, China. All the reagents and materials were used as received without further purification. 2.2. Preparation of superhydrophobic HD-POS@PET fabrics 0.05 mL of HDTMS, 0.016 mL of GPTMS and 1 mL of HCl (12 mol L-1) were added into 200 mL of H2O in a conical flask. The mixture was sonicated for 10 min, and then stirred at room temperature for 18 h to fabricate the HD-POS aqueous suspension via hydrolytic condensation of HDTMS and GPTMS. A piece of the PET fabric was immersed in the suspension for 30 min, and then treated at 130 °C in an oven for 2 h to form the HD-POS@PET fabric. 2.3. Measurement of water shedding angle (WSA) The surface of fabrics is macroscopically rough, and thus it is impossible to accurately detect the drop profile for CA measurement with Contact Angle System OCA20 (Dataphysics, Germany) equipped with a tilting table. Thus, WSA was used to evaluate the superhydrophobicity instead of CA and sliding angle according to previous studies [42,43]. A syringe was positioned with the needle (0.51 mm in diameter) tip 1 cm above the fabric, and a 10 lL water drop could contact the fabric 2 cm from its bottom end. To test the WSA, the measurements were started at an inclination angle of 1°. If there were drops remained on the fabric, the inclination angle would be increased by 1° until all drops completely rolled off the fabric. The lowest inclination angle at which all the drops completely roll off the fabric was recorded as the WSA. A
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minimum of five places were tested for each sample, and the average values with standard errors were reported (Movie S1).
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After all the durability tests, the WSA and WRG were measured to evaluate the changes in superhydrophobicity.
2.4. Evaluation of water impalement resistance 2.8. Simulated scald-preventing tests The WRG of fabrics was evaluated according to the textile spray test (ISO 4920:2012 or GB/T4745-2012), which is consistent with AATCC 22–2014. The sample was held on the equipment (Fig. S1), and then 250 mL of water was poured into the funnel quickly and sprayed onto surface of the fabric. The spray would last 25–30 s. Then, the fabric was taken down, tapped twice against a solid object to remove excess water drops, and the WRG can be obtained according to the phenomena listed in Table S1. The tests were repeated for three times for each sample, and the average values with standard errors were reported. 2.5. Washing durability test The washing durability of the fabrics was evaluated by a standard washing machine (YK-062, Dongguan Yaoke Instrument Equipment Co. Ltd., China) equipped with two 1200 mL containers according to the AATCC 61-2006 2B test method [44]. The fabric (50 mm 150 mm) was put in the container together with 150 mL of aqueous solution containing 0.15 wt% detergent and 50 stainless steel balls 6 mm in diameter. The temperature was kept at 49 °C and the stirring speed was 40 rpm. After 45 min washing, the fabric was rinsed by deionized water and dried at 60 °C. The standard washing process has the same effect t as five cycles of home machine washing, and the equivalent cycles of home washing were used in the paper. 2.6. Abrasion durability test The abrasion durability was evaluated by a Matindale tester (YK2354, Dongguan Yaoke Instrument Equipment Co. Ltd., China) which meets the standard of ASTM 4966 [31]. During the test, 12 kPa was chosen as the pressure which is usually used for heavy duty upholstery usages. A standard fabric was employed as the abradant. 2.7. Other durability tests (i) UV irradiation: The fabrics were kept in a UV testing machine (ZN-P, Shanghai Xinlang Electronic Technology Co., Ltd) and were irradiate with UV light (280–315 nm, 320 W) at 60 °C for l68 h. (ii) Corrosive liquids erosion tests: The fabrics were immersed in HCl (pH 1) and NaOH (pH 14) aqueous solutions at room temperature for a period of time. Then, the fabrics were rinsed with deionized water and dried at 60 °C. (iii) Outdoor weathering: The fabrics were hung on a clothesline from December in 2018 to April in 2019 on the roof of a building in Lanzhou, China. The temperature can be as low as 15 °C in winter. (iv) Boiling in water: The fabrics were immersed in boiling water for 225 min. Then, the fabrics were rinsed with deionized water and dried at 60 °C. (v) Thermal stability: The fabrics were kept in an oven at different temperatures (100–250 °C) for 1 h. (vi) Ultrasonic treatment: The fabrics were immersed in water or ethanol, and then treated in an ultrasonic cleaning tank for 1 h at 25 °C. (vii) Tape peeling test: An adhesive tape (3 M, scotch 600) was adhered on the fabric with 16.6 kPa pressure for 90 s, and then peeled off from the sample.
The fabric was held horizontally and an infrared camera was put along the fabric (Fig. S2a). A video camera was set behind the infrared camera in order to record the temperature change on the screen of the infrared camera. Then, 100 mL of boiling water was poured onto the fabric from 5 cm above with an impact velocity of about 1 m s 1 on the fabric, and the temperature map at the lower surface of the fabric was recorded. In another test, the fabric was inclined for 30° and an infrared camera was put vertically to and beneath the fabric (Fig. S2b). A video camera was set behind the infrared camera in order to record the temperature change on the screen of the infrared camera. Then, 100 mL of boiling water was poured onto the fabric, and the temperature map at the lower surface of the fabric was recorded.
2.9. Scald model and histological analysis All procedures in the experiments were performed in compliance with the regulations and guidelines of the National Ethics Committee on Animal Welfare of China (NFYY-2016-27). The research was endorsed by Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences. Sprague-Dawley rats (male, 6 weeks old, ca. 200 g) were used for evaluating scaldpreventing performance of the fabrics. The rats were weighed and anesthetized with pentobarbital in a sterile saline (70 mg kg 1). Then, the dorsum fur of the rats were sheared by a scissor and removed by depilatory cream (Guangzhou, Ximeng Cosmetics Co., Ltd.). Nine rats were randomly divided into three groups: PET fabric covered, HD-POS@PET fabric covered and control. Then, 40 mL of boiling water was poured onto the fabrics on the back of the rats in 2 s. The fabrics were removed after 9 s. Then, all the rats were kept in cages for the same postinjury care. The scald injuries were recorded using a camera at predetermined time intervals, and the rats were sacrificed by injection of excessive anaesthetic after 48 h. The samples on the back of the rats for histological analysis were cut and maintained in 10% neutralized formalin overnight. Then, the samples were paraffin-embedded and sectioned. The sectioned samples were stained with hematoxylin and eosin, and then observed using an optical microscope (Nikon Ds-fi3, Pooher, Co. Ltd.).
2.10. Characterization The micrographs of the samples were taken using a field emission SEM (JSM-6701F, JEOL) and a field emission TEM (JEM1200EX, FEI). Before SEM observation, all samples were fixed on copper stubs and coated with a layer of gold film. For TEM observation, a drop of the samples in ethanol was put on a copper grid and dried in the open atmosphere. FTIR spectra of samples were recorded using a Thermo Nicolet Nexus TM spectrophotometer in the range of 4,000–400 cm 1 using KBr pellets. The surface chemical composition of samples was analyzed via XPS using a VG ESCALAB 250 Xi spectrometer equipped with a monochromated AlKa Xray radiation source and a hemispherical electron analyzer. The spectra were recorded in the constant pass energy mode with a value of 100 eV, and all binding energies were calibrated using the C 1 s peak at 284.6 eV as the reference.
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Fig. 1. (a) Schematic preparation, (b) digital image and (c) TEM image of the HD-POS suspension. (d) Preparation of the HD-POS@PET fabrics. SEM images of the (e-f) PET and (g-h) HD-POS@PET fabrics.
Fig. 2. (a) Digital images of water and various aqueous liquids on the PET and HD-POS@PET fabrics. Water drops were dyed with methylene blue for clear observation. (b) Snapshots of a 10 lL water drop released from 20 cm height impacting/bouncing on the HD-POS@PET fabric. Photographs of the HD-POS@PET fabric (c) during and (d) after the spray test. (e) Photograph and infrared image of a hot water drop on the HD-POS@PET fabric. (f) Variation of WSA with water temperature. Photographs and infrared images of (g) a jet of boiling water bouncing off and (h) a cup of boiling water pouring on the HD-POS@PET fabric.
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3. Results and discussion 3.1. Preparation of HD-POS suspensions and superhydrophobic HDPOS@PET fabrics The HD-POS aqueous suspension was designed by HClcatalyzed hydrolytic condensation of HDTMS and GPTMS according to the following considerations. Durability of a coating on a substrate depends largely on the interactions between them [31,45–47]. HD-POS contains a large number of hexadecyl, –OH and Si–OH groups (Fig. 1a). The hexadecyl groups from HDTMS can reduce the surface energy, while the –OH groups from the epoxy groups of GPTMS and the Si-OH groups from hydrolysis of the silanes can enhance the interactions between HD-POS and PET fabrics. In addition, HCl is helpful to generate more Si–OH groups, as hydrolysis of silanes is dominant accompanied by mild condensation of Si–OH groups in an acidic condition [45,48,49]. After reaction at room temperature for 18 h, a milky HD-POS aqueous suspension was formed (Fig. 1b). The suspension is stable at room conditions for over three months. The HD-POS suspension is mainly composed of oligomers and polymers with sparse nanoparticles smaller than 100 nm (Fig. 1c). In the Fourier transform infrared spectrum (FTIR) of HD-POS (Fig. S3a), the broad peak at 3380 cm 1 is ascribed to stretching vibration of Si-OH and –OH groups, and the peak at 1020–1094 cm 1 is ascribed to Si-O-Si and Si-OH groups, confirming formation of HD-POS and existence of a large number of –OH and Si-OH groups [50,51]. In addition, the peaks corresponding to –CH3 (2956 cm 1), –CH2 (2919, 2851 and
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1467 cm 1), Si–C (790 cm 1) and CH2–O–CH2 (1102 cm 1) groups were observed [52-54]. Fig. 1d shows preparation of the superhydrophobic HD-POS@PET fabrics. The PET fabric is composed of microfibers 10–15 lm in diameter with smooth surface (Fig. 1e-f). The PET fabric was immersed in the HD-POS suspension for 30 min, during which HD-POS was adsorbed onto the PET microfibers by hydrogen bonding between the Si-OH and –OH groups of HD-POS and the PET fabric [44,55]. Then, the HD-POS@PET fabric was cured at 130 °C for 2 h to enhance the interactions between HD-POS and the PET fabric, and to facilitate condensation of the Si-OH groups of HD-POS. This is confirmed by the FTIR spectrum of the HD-POS powder obtained by drying the HD-POS suspension at 130 °C for 2 h (Fig. S3b). The peak attributed to the Si–OH and –OH groups (3431 cm 1) became very weak while the peak attributed to the Si–O–Si group (1020– 1094 cm 1) became very strong. Compared with the PET microfibers, the surface of the HD-POS@PET microfibers is very rough with the compact and sheet HD-POS firmly attached to the PET microfibers (Fig. 1g-h). The presence of the HD-POS coating on the PET fabric is also confirmed by XPS analysis (Fig. S4). 3.2. Superhydrophobicity of HD-POS@PET fabrics The PET fabric is hydrophilic, and can be easily wetted by water and various aqueous liquids in daily life (Fig. 2a and S5). By introducing the rough HD-POS layer with low surface energy, the HDPOS@PET fabric shows remarkable superhydrophobicity with a WSA of 6.7°, and CA around 152°. Besides water, various aqueous
Fig. 3. Effects of (a) washing, (b) abrasion, (c) cyclic stretching-releasing and (d) outdoor weathering on WSA and WRG of the HD-POS@PET fabric. SEM images of the HDPOS@PET fabric after (e-f) 200 washing cycles and (g-h) 10,000 abrasion cycles.
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liquids including sauce, coffee, vinegar and cola are all spherical on the HD-POS@PET fabric in spite of difference in the shedding angles. When a 10 lL water drop released from 20 cm height impacted the HD-POS@PET fabric, the water drop could completely bounce up and a ‘‘recoil-run” behavior of the water drop was observed (Fig. 2b and Movies S2). A continuous water jet could bounce off the fabric without leaving any trace and the fabric was strongly reflective in water (Fig. S6). Moreover, water impalement resistance of the fabric was assessed by the WRG tests according to the textile spray test (ISO 4920:2012, Fig. 2c and S1). The WRG reached 5 grades, as no water drops could be found on the fabric after the spray test (Fig. 2d and Movie S3). All these phenomena demonstrate excellent dynamic superhydrophobicity and high water impalement resistance of the HD-POS@PET fabric [56]. The dynamic water drops and jets are at the very stable Cassie-Baxter state on the fabric. Superhydrophobic fabrics with such high water impalement resistance are rare, although there are some reports about washing durable ones [8,9]. Superhydrophobicity of the HD-POS@PET fabric to hot water was also studied. Temperature of water drops (10 lL) decreased quickly during the WSA test due to heat loss (Table S2). After a 1 cm journey and sitting on the fabric, the temperature of a boiling water drop (~93 °C) decreased to ~68 °C (Fig. 2e). The hot water drop (~68 °C) has a WSA of ~17°, which is higher than that at room temperature because of decrease in water surface tension and condensation of hot vapor [12]. So, we studied the changes of the WSA with temperature of water drops after sitting on the fabric (Fig. 2f). The WSA remained around 7–9.3° at temperature below 46 °C, and then increased gradually to ~17° with increasing temperature to ~68 °C. To study the superhydrophobicity to even hotter water, a jet of boiling water was introduced on the fabric. The water jet decreased to ~76 °C after reaching the fabric, and could bounce
off quickly (Fig. 2g). Even after pouring a large amount of boiling water (100 mL) on the fabric, no water remained on the fabric although the water temperature reached ~89 °C (Fig. 2h and S7, and Movie S4). All these phenomena demonstrate excellent repellency of the fabric to hot water compared to previous studies which either caused healthy concerns becasue of use of fluorinated compounds or showed only water temperature in beakers instead of water temperature on sample surface [4,57,58]. This is attributed to the compact HD-POS layer on the PET microfibers, which effectively inhibits condensation of hot vapor into the micro-/ nanostructure. Additionally, the high stability of HD-POS as a kind of silicone material should also beneficial to the excellent repellency to hot water. 3.3. Mechanical robustness of HD-POS@PET fabrics Mechanical robustness of the HD-POS@PET fabric was studied in detail by washing, abrasion and stretching. Fig. 3a shows washing durability of the fabric assessed according to AATCC test method 61-2006 2B. After 50 cycles, the WSA remained at ~7° and the WRG kept at 4–5 grades. Then, the WSA gradually increased to 15° and the WRG decreased to 3 grades after 200 cycles. This is better than most of superhydrophobic fabrics fabricated via nonfluorinated or waterborne approaches, which can only withstand tens cycles of washing [16,44,59–62]. The decrease in superhydrophobicity is attributed to change in microstructure of the fabric (Fig. 3e-f). Some HD-POS was washed off and the surface of the HD-POS@PET microfibers became smoother after 200 washing cycles, compared to the fresh HD-POS@PET fabric. Abrasion resistance of the fabric was assessed by the Martindale method at 12 kPa. The WSA slightly decreased from 8° to 6° after the first 500 abrasion cycles (Fig. 3b), which is perhaps owing to roughness increase caused by abrasion [63]. Then, the WSA
Fig. 4. (a) Horizontal view of temperature change at lower surface of the fabrics with time, and infrared images of the (b) PET and (c) HD-POS@PET fabrics. (d) Vertical view of temperature change at lower surface of the fabrics with time, and infrared images of the (e) PET and (f) HD-POS@PET fabrics.
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gradually increased to 19° after 10,000 cycles. Meanwhile, the WRG decreased to 3 grades after 1000 cycles, and stayed at 2 grades in the following 9000 cycles. The HD-POS@PET fabric performed better than many existing counterparts in the abrasion test [7,16,40,59,64,65]. The decrease in superhydrophobicity is because some microfibers were broken and the surface of the microfibers became smoother after long-term intensive abrasion (Fig. 3g-h). The stability of the HD-POS@PET fabric against tape peeling is shown in Fig. S8. The WSA deceased a little to 10° and the WRG decreased to 4 grades after 10 peeling cycles. 100 cycles later, the WSA was still around 15°, and the WRG was 3 grades, indicating high stability of the facric against tape peeling. Clothes are frequently deformed during body movements, and mechanical deformation often leads to micro-/nanostructure changes of superhydrophobic layers, resulting in deterioration or even loss of superhydrophobicty [66]. The WSA of the HDPOS@PET fabric kept below 8° with stretching strain up to 150%, and then gradually increased to ~15° when the strain was 300% (Fig. S9). Furthermore, the WSA remained at ~9° and the WRG kept at 4 grades after 1000 cycles of cyclic stretching-releasing at 100% strain (Fig. 3c). The retaining of superhydrophobicity at high strain and after cyclic stretching-releasing demonstrates excellent stretching durability of the fabric. The excellent mechanical durability of the HD-POS@PET fabric is owing to i) the hierarchical micro-/nanostructure formed by combination of microstructure of the PET fabric and nanostructure of the HD-POS layer, ii) stable bonding of HD-POS on the PET microfibers, and iii) inherent high stability and elasticity of HD-
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POS as a silicone material [67–69]. These are also responsible for the excellent environmental and chemical durability of the fabric as shown below. 3.4. Environmental and chemical robustness of HD-POS@PET fabrics The HD-POS@PET fabric did not show obvious change in the WSA and WRG after UV irradiation for 7 days (Fig. S10), ensuring long-term outdoor applications. The environmental robustness of the fabric was further tested by outdoor weathering (Fig. 3d). The superhydrophobicity kept unchanged until the snows on Dec. 28 and 31, which led to increase in the WSA to 15° and decrease of the WRG to 4 grades, which might because the surface was slightly contaminated by the impurities in the snows. The WSA gradually increased but the WRG unchanged with prolonged outdoor weathering. However, after 77 days, the superhydrophobicity was improved as the WSA decreased to 17°. This is ascribed to temperature rise in spring, leading to diffusion of HD-POS to the surface of the fabric to minimize the surface energy. Heat treatment can improve superhydrophobicity or superamphiphobicity by migration of silicone materials to the surface of damaged coatings [36,50]. Finally, the WSA was ~21° and the WRG was 3 grades after 117 days (on Apr. 21, 2019), indicating long-term durability of the fabric in outdoor conditions. Chemical durability of the HD-POS@PET fabric was evaluated by various approaches. After 7 days immersion in HCl solution (pH 1) or NaOH solution (pH 14), the WSA was ~ 8° and the WRG stayed at 4-5 grades (Fig. S11a). After 225 min in boiling water, the WSA was
Fig. 5. Digital images, infrared images and schematic illustrations of the boiling water scald models on rat dorsum covered by the (a-c) PET and (d-f) HD-POS@PET fabrics. The arrows in the infrared images show heads of the rats.
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~13° and the WRG stayed at 4 grades (Fig. S11b). The fabric also showed excellent thermostability up to 250 °C (Fig. S11c). Moreover, ultrasonic treatment in water or ethanol for 60 min resulted in negligible changes in the WSA and WRG (Fig. S11d). 3.5. HD-POS@PET fabrics for preventing scald To find out the difference between the PET and HD-POS@PET fabrics when contacting with boiling water, infrared camera and video camera were employed to record the process of pouring 100 mL of boiling water on the fabrics (20 20 cm) from both horizontal and vertical views (Fig. S2). From the horizontal view (Fig. 4a-b and Movie S5), all the hot water quickly wetted and penetrated the PET fabric. The water temperature at lower surface of the PET fabric was as high as 85.5 °C after 1.5 s and was still above 60 °C after 6 s. Hot water stayed in the fabric even after 9 s. From the vertical view (Fig. 4d-e and Movie S6), the water temperature at lower surface of the PET fabric was still above 70 °C after 9 s, and all the wetted area was at very high temperature. The high temperature area reached 2/3 of the fabric. A large amount of hot water above 70 °C with such long contact time and large contact area would cause serious scald. Differently, boiling water could not penetrate the HD-POS@PET fabric but rolled off the fabric from the edge (Movie S5). The hot water completely left the fabric in 3 s. Although the temperature at the lower surface of the HD-POS@PET fabric reached 80.4 °C after 1.5 s, the temperature dropped quickly to 60 °C in 2.7 s (Fig. 4a, c), which is much shorter than the minimum duration (5 s) to cause scald [1,3,6]. The temperature difference between the PET and HD-POS@PET fabrics could be seen more
clearly from the vertical view (Fig. 4d-f and Movie S6). The temperature dropped quickly to 60 °C in 3.2 s, to 39.2 °C in 4.5 s, and to room temperature in 8.0 s. Also, the high temperature area was no more than 1/2 of the fabric. The temperature increase at the lower surface of the HD-POS@PET fabric is attributed to heat conduction and radiation through the fabric as well as diffusion of a small amount of hot vapor [70]. The above results demonstrate that the HD-POS@PET fabric cools down much more quickly than the PET fabric by efficiently inhibiting hot water penetration, reducing contact time and contact area with hot water, and thus could probably be used for scald-preventing. The scald-preventing performance of the HD-POS@PET fabric was studied by a boiling water scald model on rats dorsum. Once encountering boiling water, the PET fabric was immediately wetted and the temperature at upper surface of the fabric sharply increased to ~89 °C after 1 s (Fig. 5a–c and S12a). All the hot water and most of the hot vapor penetrated the PET fabric and contacted with the skin. The temperature was still as high as 82 °C after 2 s and 58 °C after 9 s, which could still cause scald to the skin [4]. The temperature of the area between the fabric and the rats dorsum must be even higher due to slow heat conduction and radiation, condensation of hot vapor and hot water cooling. Differently, for the HD-POS@PET fabric, boiling water rapidly rolled off once contacting with the fabric (Fig. 5d–f and S12b), avoiding direct contact of hot water with rats dorsum and inhibiting penetration of most of hot vapor. Thus, the temperature at upper surface of the fabric increased to 77 °C after 1 s, but dropped quickly to ~64 °C after 2 s and to ~35 °C after 9 s owing to evidently reduced contact time and contact area with hot water.
Fig. 6. Digital images of rat dorsum and histology images of rat dorsum skin covered with the (a, b) PET and (c, d) HD-POS@PET fabrics after the scald test with (e, f) the control group for comparison.
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To evaluate the scald injuries, the changes of the dorsum skin were tracked for 48 h. At the moment after the scald test, the rats dorsum of all the three groups did not show visible difference. However, 6 h later, wound appeared on the rats dorsum covered with the PET fabric (Fig. 6a and S13a). The scald injury was very evident after 24 h, almost the same as 48 h later. The bottom side was bright-red due to loss of the epidermis, and the top part was pale and swollen. Then, the dorsum samples were cut, sectioned and observed by optical microscope (Fig. 6b and S13b). Some epidermis disappeared, pyknosis and extensive necrosis were observed in the keratinocyte nuclei (blue arrows), and the follicle-like structures were damaged (green arrows). These results indicate serious scald injury. However, the dorsum skin covered with the HD-POS@PET fabric did not show any evident difference in 48 h compared with the control group (Fig. 6c, e and S13c, e). The rats dorsum was even covered with new hairs after 48 h, indicating that the skin was healthy. From the dorsum skin histology images (Fig. 6d, f and S13d, f), no difference can be found between the HD-POS@PET fabric covered group and the control group, except that acidophilia of collagen decreased due to very slight edema in the corium (black arrows). Due to excellent hot water repellency and water impalement resistance, the HD-POS@PET fabric can (i) avoid direct contact of hot water and vapor with rat skin by preventing penetration of hot water and most of vapor, (ii) reduce heat conduction and radiation to rat skin by reducing contact time and contact area of hot water with the fabric. Consequently, the HD-POS@PET fabric kept dry and the temperature of the fabric in contact with the skin was much lower than that of the PET fabric once encountering hot water, ensuring efficient scald-preventing. 4. Conclusions In summary, we have demonstrated the creation of a robust HD-POS@PET fabric with excellent hot water repellency and water impalement resistance for efficient scald-preventing via a simple waterborne and nonfluorinated approach. The fabric features excellent hot water repellency even for dynamic boiling water and high water impalement resistance of 5 grades. Moreover, the fabric shows high mechanical, environmental and chemical robustness in various harsh conditions such as 200 cyles washing, 10,000 cycles abrasion, 100 cycles tape peeling, 1000 cycles 100% stretching and releasing, 168 h UV irradiation, 168 h corrosive liquids erosion and 117 days outdoor weathering, which is superior to most of previous studies [44,62]. These extraordinary properties are attributed to hierarchical micro-/nanostructure of the fabric, stable bonding of the compact HD-POS layer on the PET microfibers, and inherent high stability and elasticity of HD-POS as a silicone material. The fabric demonstrates efficient scald-preventing performance according to the simulation experiments. Hot water can completely leave the HD-POS@PET fabric in 3 s, and the surface temperature decreased to 60 °C 10 s quicker than the pristine fabric. Furthermore, the scald model on rats dorsum and histological analysis demonstrate that the rats covered with the pristine fabric was injuried seriouly, while those covered with the HD-POS@PET fabric were perfectly protected, reflecting that the HD-POS@PET fabric can indeed avoid direct contact of hot water and vapor with rat skin, and reduce heat conduction and radiation to rat skin. The biomimetic fabric might be used to avoid or at least alleviate most of scald injuries in our daily life rather than treatment after scald. CRediT authorship contribution statement Ning Tian: Conceptualization, Methodology, Investigation, Writing - original draft. Jinfei Wei: Methodology, Investigation.
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Yabin Li: Investigation, Data curation. Bucheng Li: Methodology, Investigation. Junping Zhang: Conceptualization, Supervision, Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This study was supported by the National Natural Science Foundation of China (51873220), and the Funds for Creative Research Groups of Gansu, China (17JR5RA306). Appendix A. Supplementary material Supplementary data to this article can be found online at https://doi.org/10.1016/j.jcis.2020.01.067. References [1] M. Stone, J. Ahmed, J. Evans, The continuing risk of domestic hot water scalds to the elderly, Burns 26 (2000) 347–350. [2] T.W. Chiu, D.C. Ng, A. Burd, Properties of matter matter in assessment of scald injuries, Burns 33 (2007) 185–188. [3] C. Loller, G.A. Buxton, T.L. Kerzmann, Hot soup! Correlating the severity of liquid scald burns to fluid and biomedical properties, Burns 42 (2016) 589– 597. [4] Y. Liu, X. Chen, J.H. Xin, Can superhydrophobic surfaces repel hot water?, J. Mater. Chem. 19 (2009) 5602. [5] M.H. Toon, D.M. Maybauer, L.L. Arceneaux, J.F. Fraser, W. Meyer, A. Runge, M.O. Maybauer, Children with burn injuries–assessment of trauma, neglect, violence and abuse, J. Inj. Violence Res. 3 (2011) 98–110. [6] E.M. Quist, M. Tanabe, J.E. Mansell, J.L. Edwards, A case series of thermal scald injuries in dogs exposed to hot water from garden hoses (garden hose scalding syndrome), Vet. Dermatol. 23 (2012) 162–166. e33. [7] M. Wu, B. Ma, T. Pan, S. Chen, J. Sun, Silver-nanoparticle-colored cotton fabrics with tunable colors and durable antibacterial and self-healing superhydrophobic properties, Adv. Funct. Mater. 26 (2016) 569–576. [8] H. Zhou, H. Wang, H. Niu, A. Gestos, X. Wang, T. Lin, Fluoroalkyl silane modified silicone rubber/nanoparticle composite: a super durable, robust superhydrophobic fabric coating, Adv. Mater. 24 (2012) 2409–2412. [9] B. Deng, R. Cai, Y. Yu, H. Jiang, C. Wang, J. Li, L. Li, M. Yu, J. Li, L. Xie, Laundering durability of superhydrophobic cotton fabric, Adv. Mater. 22 (2010) 5473– 5477. [10] Q. Zhu, Q. Gao, Y. Guo, C.Q. Yang, L. Shen, Modified silica sol coatings for highly hydrophobic cotton and polyester fabrics using a one-step procedure, Ind. Eng. Chem. Res. 50 (2011) 5881–5888. [11] Q. Ma, B. Wang, J. Xu, J. Lv, H. Li, Y. Li, C. Zhao, Preparation of superhydrophobic polyester fabric by growing polysiloxane microtube and its application, Silicon 10 (2018) 2009–2014. [12] B. Li, J. Zhang, Durable and self-healing superamphiphobic coatings repellent even to hot liquids, Chem. Commun. (Camb) 52 (2016) 2744–2747. [13] T. Mouterde, P. Lecointre, G. Lehoucq, A. Checco, C. Clanet, D. Quere, Two recipes for repelling hot water, Nat. Commun. 10 (2019) 1410. [14] M. Cao, X. Luo, H. Ren, J. Feng, Hot water-repellent and mechanically durable superhydrophobic mesh for oil/water separation, J. Colloid Interface Sci. 512 (2018) 567–574. [15] J. Zhang, B. Li, L. Wu, A. Wang, Facile preparation of durable and robust superhydrophobic textiles by dip coating in nanocomposite solution of organosilanes, Chem. Commun. (Camb) 49 (2013) 11509–11511. [16] C.-H. Xue, Y.-R. Li, J.-L. Hou, L. Zhang, J.-Z. Ma, S.-T. Jia, Self-roughened superhydrophobic coatings for continuous oil–water separation, J. Mater. Chem. A 3 (2015) 10248–10253. [17] Z. Du, P. Ding, X. Tai, Z. Pan, H. Yang, Facile preparation of Ag-coated superhydrophobic/superoleophilic mesh for efficient oil/water separation with excellent corrosion resistance, Langmuir 34 (2018) 6922–6929. [18] P. Raturi, K. Yadav, J.P. Singh, ZnO-nanowires-coated smart surface mesh with reversible wettability for efficient on-demand oil/water separation, ACS Appl. Mater. Interfaces 9 (2017) 6007–6013. [19] E.J. Falde, S.T. Yohe, Y.L. Colson, M.W. Grinstaff, Superhydrophobic materials for biomedical applications, Biomaterials 104 (2016) 87–103. [20] Z. Qin, J. Liu, X. Zeng, A simple way to achieve superhydrophobic surfaces with tunable water adhesion by a nanosecond pulse laser, SPIE/COS Photonics Asia 10813 (2018) 14.
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Journal of Colloid and Interface Science journal homepage: www.elsevier.com/locate/jcis
Efficient scald-preventing enabled by robust polyester fabrics with hot water repellency and water impalement resistance Ning Tian a,b, Jinfei Wei a, Yabin Li a, Bucheng Li a, Junping Zhang a,b,⇑ a b
Center of Eco-material and Green Chemistry, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, PR China
g r a p h i c a l a b s t r a c t
a r t i c l e
i n f o
Article history: Received 18 October 2019 Revised 17 January 2020 Accepted 18 January 2020 Available online 20 January 2020 Keywords: Hot water repellency Scald-preventing Superhydrophobic Surface chemistry Silanes
a b s t r a c t Scald is a kind of common injury for human beings caused by contacting with hot liquids and/or vapor. Herein, we report the preparation of an advanced fabric for efficient scald-preventing by dip-coating a common polyester fabric in a hexadecyl polysiloxane (HD-POS) aqueous suspension, which was synthesized via a waterborne and nonfluorinated approach. Thanks to the hierarchical micro-/nanostructure of the fabric, stable bonding of the compact HD-POS layer on the polyester microfibers, and inherent high stability and elasticity of HD-POS, the fabric features excellent hot water repellency even for dynamic boiling water with a high water impalement resistance of up to 5 grades according to the water repellency grade test. In addition, the fabric shows extraordinary mechanical stability, e.g., its superhydrophobicity remained nearly unchanged after 200 cycles washing, 10,000 cycles Martindale abraison or 1000 cycles 100% streching and releasing. It also exhibits superior environmental robustness (117 d outdoor test) and chemical robustness (7 d immersion in 1 M HCl or NaOH solution, 60 min ultrosonication in both water and anchol immersion) in various harsh conditions. By applying as an advanced fabric for efficient scald-preventing, it can avoid direct contact of hot water and vapor with rat skin by preventing penetration of hot water and most of vapor. It could also significantly reduce heat conduction and radiation to rat skin by reducing contact time of hot water with the fabric (decreased 10 s more quickly than the pristine fabric to 60 °C when encountering 100 mL of 92 °C water). As a result, the fabric in contact with the skin keeps dry and the fabric temperature is much lower than that of the pristine fabric once
⇑ Corresponding author at: Center of Eco-material and Green Chemistry, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China. E-mail address: [email protected] (J. Zhang). https://doi.org/10.1016/j.jcis.2020.01.067 0021-9797/Ó 2020 Elsevier Inc. All rights reserved.
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encountering hot water, thus showing great potentials as an advanced fabric for efficient scaldpreventing applications. Ó 2020 Elsevier Inc. All rights reserved.
1. Introduction Scald is a kind of common injury for human beings, especially for children and elderly people, usually caused by contacting with hot liquids and/or vapor [1–3]. More than 110,000 people are treated in hospital because of scalds every year [4]. Usually, scald is not fatal, but may cause intense pain, infection and fester for a long time, and leave scarring and emotional hurt [5]. In the most of scald cases, hot water wets and penetrates through the clothes of victims along with hot vapor, causing scald by heat from the hot water itself and condensation of the vapor [4]. Severity of scald depends on temperature of hot water and vapor, water-skin contact time and contact area, etc. Scald happened in 30 s at 55 °C and in 5 s at 60 °C for adults, and in shorter time and at lower temperature for children because of their thin skin [1,3,6]. This means common clothes would actually aggravate scald severity, as they can be easily wetted and penetrated by hot water and vapor [2]. Therefore, there is an urgent need for developing advanced fabrics to reduce or even prevent wetting and penetration of hot water and vapor and then to avoid or at least alleviate most of scalds. Superhydrophobic fabrics are of great interest because of their high repellency to water [7–11]. Although superhydrophobic fabrics can prevent wetting by room temperature water, their hot water repellency and water impalement resistance are seldom studied. Most of natural and artificial superhydrophobic surfaces lose superhydrophobicity once encountered with hot water, owing to the lower surface tension of hot water and condensation of hot vapor into the micro-/nanostructures [12–14]. Though the employment of superhydrophobic fabrics for scald-preventing applications has been reported [4], few studies involved heat distribution, duration time of hot water or animal scald model test. On the other hand, the assessment of superhydrophobicity now largely depends on the water contact angle (CA), CA hysteresis or sliding angle [15–20], which is acctrually insufficient to evaluate their performance in terms to scald-preventing applications. High water impalement resistance of superhydrophobic surfaces is imperative for many of their applications including airplanes, trains, wind turbine blades and clothes.[21,22] Though great progress in superhydrophobic surfaces has been achieved in the past two decades, only a few examples show hot water repellency or high water impalement resistance [12,21,23,24]. Meanwhile, superhydrophobic fabrics with such merits have not been reported. Safety issues are one of great concerns for preparation of superhydrophobic fabrics, of which fluorinated compounds and organic solvents are frequently used [25–27]. The fluorinated compounds are not degradable and may cause bioaccumulation [28], leading to prohibition in the USA and EU countries [29,30]. In the textile dyeing and finishing industry, almost all processes are waterborne and the use of organic solvents will make a technique impractical because of safety concern [31]. It remains challenging to prepare robust superhydrophobic fabrics via waterborne and nonfluorinated approaches. Poor mechanical durability is a fatal defect of superhydrophobic surfaces [32–34]. The combination of inherent microstructure of fabrics and covalent bonding of coatings onto the fabrics could improve mechanical durability [35–37]. However, the waterborne and/or nonfluorinated superhydrophobic fabrics developed so far could withstand very limited washing and abrasion [38]. Hence, superhydrophobic fabrics that can withstand washing, abrasion,
stretching and outdoor settings are highly desired. Moreover, functional superhydrophobic fabrics with additional features besides self-cleaning are receiving increasing attention to meet diverse applications, e.g., pressure sensors, electromagnetic interference shielding and supercapacitor [39–41]. Here, we report a waterborne and nonfluorinated approach for preparing robust superhydrophobic polyester (PET) fabrics with excellent hot water repellency and water impalement resistance for efficient scald-preventing. First, a hexadecyl polysiloxane (HD-POS) aqueous suspension was prepared by hydrolytic condensation of hexadecyltrimethoxysilane (HDTMS) and (3-glycidyloxy propyl)trimethoxysilane (GPTMS). Then, the superhydrophobic HD-POS@PET fabrics were prepared by dip-coating in the HDPOS aqueous suspension. The superhydrophobic HD-POS@PET fabrics feature (i) excellent hot water repellency even for dynamic boiling water, (ii) high water impalement resistance of 5 grades according to the water repellency grade (WRG) test, and (iii) extraordinary robustness against washing, abrasion, UV irradiation, corrosive liquids erosion and outdoor weathering, etc. Furthermore, the HD-POS@PET fabrics can efficiently prevent scald by hot water, which was proved for the first time by simulated test and rat scald model test. 2. Materials and methods 2.1. Materials The PET fabric was supplied by Bevery, Shanghai China. HDTMS (98%) and GPTMS (98%) were bought from Gelest. HCl (36–38%) and NaOH (99.7%) were bought from China National Medicines Co. Ltd. Sauce, coffe, vinegar and cola were bought from a supermarket in Lanzhou, China. All the reagents and materials were used as received without further purification. 2.2. Preparation of superhydrophobic HD-POS@PET fabrics 0.05 mL of HDTMS, 0.016 mL of GPTMS and 1 mL of HCl (12 mol L-1) were added into 200 mL of H2O in a conical flask. The mixture was sonicated for 10 min, and then stirred at room temperature for 18 h to fabricate the HD-POS aqueous suspension via hydrolytic condensation of HDTMS and GPTMS. A piece of the PET fabric was immersed in the suspension for 30 min, and then treated at 130 °C in an oven for 2 h to form the HD-POS@PET fabric. 2.3. Measurement of water shedding angle (WSA) The surface of fabrics is macroscopically rough, and thus it is impossible to accurately detect the drop profile for CA measurement with Contact Angle System OCA20 (Dataphysics, Germany) equipped with a tilting table. Thus, WSA was used to evaluate the superhydrophobicity instead of CA and sliding angle according to previous studies [42,43]. A syringe was positioned with the needle (0.51 mm in diameter) tip 1 cm above the fabric, and a 10 lL water drop could contact the fabric 2 cm from its bottom end. To test the WSA, the measurements were started at an inclination angle of 1°. If there were drops remained on the fabric, the inclination angle would be increased by 1° until all drops completely rolled off the fabric. The lowest inclination angle at which all the drops completely roll off the fabric was recorded as the WSA. A
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minimum of five places were tested for each sample, and the average values with standard errors were reported (Movie S1).
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After all the durability tests, the WSA and WRG were measured to evaluate the changes in superhydrophobicity.
2.4. Evaluation of water impalement resistance 2.8. Simulated scald-preventing tests The WRG of fabrics was evaluated according to the textile spray test (ISO 4920:2012 or GB/T4745-2012), which is consistent with AATCC 22–2014. The sample was held on the equipment (Fig. S1), and then 250 mL of water was poured into the funnel quickly and sprayed onto surface of the fabric. The spray would last 25–30 s. Then, the fabric was taken down, tapped twice against a solid object to remove excess water drops, and the WRG can be obtained according to the phenomena listed in Table S1. The tests were repeated for three times for each sample, and the average values with standard errors were reported. 2.5. Washing durability test The washing durability of the fabrics was evaluated by a standard washing machine (YK-062, Dongguan Yaoke Instrument Equipment Co. Ltd., China) equipped with two 1200 mL containers according to the AATCC 61-2006 2B test method [44]. The fabric (50 mm 150 mm) was put in the container together with 150 mL of aqueous solution containing 0.15 wt% detergent and 50 stainless steel balls 6 mm in diameter. The temperature was kept at 49 °C and the stirring speed was 40 rpm. After 45 min washing, the fabric was rinsed by deionized water and dried at 60 °C. The standard washing process has the same effect t as five cycles of home machine washing, and the equivalent cycles of home washing were used in the paper. 2.6. Abrasion durability test The abrasion durability was evaluated by a Matindale tester (YK2354, Dongguan Yaoke Instrument Equipment Co. Ltd., China) which meets the standard of ASTM 4966 [31]. During the test, 12 kPa was chosen as the pressure which is usually used for heavy duty upholstery usages. A standard fabric was employed as the abradant. 2.7. Other durability tests (i) UV irradiation: The fabrics were kept in a UV testing machine (ZN-P, Shanghai Xinlang Electronic Technology Co., Ltd) and were irradiate with UV light (280–315 nm, 320 W) at 60 °C for l68 h. (ii) Corrosive liquids erosion tests: The fabrics were immersed in HCl (pH 1) and NaOH (pH 14) aqueous solutions at room temperature for a period of time. Then, the fabrics were rinsed with deionized water and dried at 60 °C. (iii) Outdoor weathering: The fabrics were hung on a clothesline from December in 2018 to April in 2019 on the roof of a building in Lanzhou, China. The temperature can be as low as 15 °C in winter. (iv) Boiling in water: The fabrics were immersed in boiling water for 225 min. Then, the fabrics were rinsed with deionized water and dried at 60 °C. (v) Thermal stability: The fabrics were kept in an oven at different temperatures (100–250 °C) for 1 h. (vi) Ultrasonic treatment: The fabrics were immersed in water or ethanol, and then treated in an ultrasonic cleaning tank for 1 h at 25 °C. (vii) Tape peeling test: An adhesive tape (3 M, scotch 600) was adhered on the fabric with 16.6 kPa pressure for 90 s, and then peeled off from the sample.
The fabric was held horizontally and an infrared camera was put along the fabric (Fig. S2a). A video camera was set behind the infrared camera in order to record the temperature change on the screen of the infrared camera. Then, 100 mL of boiling water was poured onto the fabric from 5 cm above with an impact velocity of about 1 m s 1 on the fabric, and the temperature map at the lower surface of the fabric was recorded. In another test, the fabric was inclined for 30° and an infrared camera was put vertically to and beneath the fabric (Fig. S2b). A video camera was set behind the infrared camera in order to record the temperature change on the screen of the infrared camera. Then, 100 mL of boiling water was poured onto the fabric, and the temperature map at the lower surface of the fabric was recorded.
2.9. Scald model and histological analysis All procedures in the experiments were performed in compliance with the regulations and guidelines of the National Ethics Committee on Animal Welfare of China (NFYY-2016-27). The research was endorsed by Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences. Sprague-Dawley rats (male, 6 weeks old, ca. 200 g) were used for evaluating scaldpreventing performance of the fabrics. The rats were weighed and anesthetized with pentobarbital in a sterile saline (70 mg kg 1). Then, the dorsum fur of the rats were sheared by a scissor and removed by depilatory cream (Guangzhou, Ximeng Cosmetics Co., Ltd.). Nine rats were randomly divided into three groups: PET fabric covered, HD-POS@PET fabric covered and control. Then, 40 mL of boiling water was poured onto the fabrics on the back of the rats in 2 s. The fabrics were removed after 9 s. Then, all the rats were kept in cages for the same postinjury care. The scald injuries were recorded using a camera at predetermined time intervals, and the rats were sacrificed by injection of excessive anaesthetic after 48 h. The samples on the back of the rats for histological analysis were cut and maintained in 10% neutralized formalin overnight. Then, the samples were paraffin-embedded and sectioned. The sectioned samples were stained with hematoxylin and eosin, and then observed using an optical microscope (Nikon Ds-fi3, Pooher, Co. Ltd.).
2.10. Characterization The micrographs of the samples were taken using a field emission SEM (JSM-6701F, JEOL) and a field emission TEM (JEM1200EX, FEI). Before SEM observation, all samples were fixed on copper stubs and coated with a layer of gold film. For TEM observation, a drop of the samples in ethanol was put on a copper grid and dried in the open atmosphere. FTIR spectra of samples were recorded using a Thermo Nicolet Nexus TM spectrophotometer in the range of 4,000–400 cm 1 using KBr pellets. The surface chemical composition of samples was analyzed via XPS using a VG ESCALAB 250 Xi spectrometer equipped with a monochromated AlKa Xray radiation source and a hemispherical electron analyzer. The spectra were recorded in the constant pass energy mode with a value of 100 eV, and all binding energies were calibrated using the C 1 s peak at 284.6 eV as the reference.
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Fig. 1. (a) Schematic preparation, (b) digital image and (c) TEM image of the HD-POS suspension. (d) Preparation of the HD-POS@PET fabrics. SEM images of the (e-f) PET and (g-h) HD-POS@PET fabrics.
Fig. 2. (a) Digital images of water and various aqueous liquids on the PET and HD-POS@PET fabrics. Water drops were dyed with methylene blue for clear observation. (b) Snapshots of a 10 lL water drop released from 20 cm height impacting/bouncing on the HD-POS@PET fabric. Photographs of the HD-POS@PET fabric (c) during and (d) after the spray test. (e) Photograph and infrared image of a hot water drop on the HD-POS@PET fabric. (f) Variation of WSA with water temperature. Photographs and infrared images of (g) a jet of boiling water bouncing off and (h) a cup of boiling water pouring on the HD-POS@PET fabric.
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3. Results and discussion 3.1. Preparation of HD-POS suspensions and superhydrophobic HDPOS@PET fabrics The HD-POS aqueous suspension was designed by HClcatalyzed hydrolytic condensation of HDTMS and GPTMS according to the following considerations. Durability of a coating on a substrate depends largely on the interactions between them [31,45–47]. HD-POS contains a large number of hexadecyl, –OH and Si–OH groups (Fig. 1a). The hexadecyl groups from HDTMS can reduce the surface energy, while the –OH groups from the epoxy groups of GPTMS and the Si-OH groups from hydrolysis of the silanes can enhance the interactions between HD-POS and PET fabrics. In addition, HCl is helpful to generate more Si–OH groups, as hydrolysis of silanes is dominant accompanied by mild condensation of Si–OH groups in an acidic condition [45,48,49]. After reaction at room temperature for 18 h, a milky HD-POS aqueous suspension was formed (Fig. 1b). The suspension is stable at room conditions for over three months. The HD-POS suspension is mainly composed of oligomers and polymers with sparse nanoparticles smaller than 100 nm (Fig. 1c). In the Fourier transform infrared spectrum (FTIR) of HD-POS (Fig. S3a), the broad peak at 3380 cm 1 is ascribed to stretching vibration of Si-OH and –OH groups, and the peak at 1020–1094 cm 1 is ascribed to Si-O-Si and Si-OH groups, confirming formation of HD-POS and existence of a large number of –OH and Si-OH groups [50,51]. In addition, the peaks corresponding to –CH3 (2956 cm 1), –CH2 (2919, 2851 and
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1467 cm 1), Si–C (790 cm 1) and CH2–O–CH2 (1102 cm 1) groups were observed [52-54]. Fig. 1d shows preparation of the superhydrophobic HD-POS@PET fabrics. The PET fabric is composed of microfibers 10–15 lm in diameter with smooth surface (Fig. 1e-f). The PET fabric was immersed in the HD-POS suspension for 30 min, during which HD-POS was adsorbed onto the PET microfibers by hydrogen bonding between the Si-OH and –OH groups of HD-POS and the PET fabric [44,55]. Then, the HD-POS@PET fabric was cured at 130 °C for 2 h to enhance the interactions between HD-POS and the PET fabric, and to facilitate condensation of the Si-OH groups of HD-POS. This is confirmed by the FTIR spectrum of the HD-POS powder obtained by drying the HD-POS suspension at 130 °C for 2 h (Fig. S3b). The peak attributed to the Si–OH and –OH groups (3431 cm 1) became very weak while the peak attributed to the Si–O–Si group (1020– 1094 cm 1) became very strong. Compared with the PET microfibers, the surface of the HD-POS@PET microfibers is very rough with the compact and sheet HD-POS firmly attached to the PET microfibers (Fig. 1g-h). The presence of the HD-POS coating on the PET fabric is also confirmed by XPS analysis (Fig. S4). 3.2. Superhydrophobicity of HD-POS@PET fabrics The PET fabric is hydrophilic, and can be easily wetted by water and various aqueous liquids in daily life (Fig. 2a and S5). By introducing the rough HD-POS layer with low surface energy, the HDPOS@PET fabric shows remarkable superhydrophobicity with a WSA of 6.7°, and CA around 152°. Besides water, various aqueous
Fig. 3. Effects of (a) washing, (b) abrasion, (c) cyclic stretching-releasing and (d) outdoor weathering on WSA and WRG of the HD-POS@PET fabric. SEM images of the HDPOS@PET fabric after (e-f) 200 washing cycles and (g-h) 10,000 abrasion cycles.
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liquids including sauce, coffee, vinegar and cola are all spherical on the HD-POS@PET fabric in spite of difference in the shedding angles. When a 10 lL water drop released from 20 cm height impacted the HD-POS@PET fabric, the water drop could completely bounce up and a ‘‘recoil-run” behavior of the water drop was observed (Fig. 2b and Movies S2). A continuous water jet could bounce off the fabric without leaving any trace and the fabric was strongly reflective in water (Fig. S6). Moreover, water impalement resistance of the fabric was assessed by the WRG tests according to the textile spray test (ISO 4920:2012, Fig. 2c and S1). The WRG reached 5 grades, as no water drops could be found on the fabric after the spray test (Fig. 2d and Movie S3). All these phenomena demonstrate excellent dynamic superhydrophobicity and high water impalement resistance of the HD-POS@PET fabric [56]. The dynamic water drops and jets are at the very stable Cassie-Baxter state on the fabric. Superhydrophobic fabrics with such high water impalement resistance are rare, although there are some reports about washing durable ones [8,9]. Superhydrophobicity of the HD-POS@PET fabric to hot water was also studied. Temperature of water drops (10 lL) decreased quickly during the WSA test due to heat loss (Table S2). After a 1 cm journey and sitting on the fabric, the temperature of a boiling water drop (~93 °C) decreased to ~68 °C (Fig. 2e). The hot water drop (~68 °C) has a WSA of ~17°, which is higher than that at room temperature because of decrease in water surface tension and condensation of hot vapor [12]. So, we studied the changes of the WSA with temperature of water drops after sitting on the fabric (Fig. 2f). The WSA remained around 7–9.3° at temperature below 46 °C, and then increased gradually to ~17° with increasing temperature to ~68 °C. To study the superhydrophobicity to even hotter water, a jet of boiling water was introduced on the fabric. The water jet decreased to ~76 °C after reaching the fabric, and could bounce
off quickly (Fig. 2g). Even after pouring a large amount of boiling water (100 mL) on the fabric, no water remained on the fabric although the water temperature reached ~89 °C (Fig. 2h and S7, and Movie S4). All these phenomena demonstrate excellent repellency of the fabric to hot water compared to previous studies which either caused healthy concerns becasue of use of fluorinated compounds or showed only water temperature in beakers instead of water temperature on sample surface [4,57,58]. This is attributed to the compact HD-POS layer on the PET microfibers, which effectively inhibits condensation of hot vapor into the micro-/ nanostructure. Additionally, the high stability of HD-POS as a kind of silicone material should also beneficial to the excellent repellency to hot water. 3.3. Mechanical robustness of HD-POS@PET fabrics Mechanical robustness of the HD-POS@PET fabric was studied in detail by washing, abrasion and stretching. Fig. 3a shows washing durability of the fabric assessed according to AATCC test method 61-2006 2B. After 50 cycles, the WSA remained at ~7° and the WRG kept at 4–5 grades. Then, the WSA gradually increased to 15° and the WRG decreased to 3 grades after 200 cycles. This is better than most of superhydrophobic fabrics fabricated via nonfluorinated or waterborne approaches, which can only withstand tens cycles of washing [16,44,59–62]. The decrease in superhydrophobicity is attributed to change in microstructure of the fabric (Fig. 3e-f). Some HD-POS was washed off and the surface of the HD-POS@PET microfibers became smoother after 200 washing cycles, compared to the fresh HD-POS@PET fabric. Abrasion resistance of the fabric was assessed by the Martindale method at 12 kPa. The WSA slightly decreased from 8° to 6° after the first 500 abrasion cycles (Fig. 3b), which is perhaps owing to roughness increase caused by abrasion [63]. Then, the WSA
Fig. 4. (a) Horizontal view of temperature change at lower surface of the fabrics with time, and infrared images of the (b) PET and (c) HD-POS@PET fabrics. (d) Vertical view of temperature change at lower surface of the fabrics with time, and infrared images of the (e) PET and (f) HD-POS@PET fabrics.
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gradually increased to 19° after 10,000 cycles. Meanwhile, the WRG decreased to 3 grades after 1000 cycles, and stayed at 2 grades in the following 9000 cycles. The HD-POS@PET fabric performed better than many existing counterparts in the abrasion test [7,16,40,59,64,65]. The decrease in superhydrophobicity is because some microfibers were broken and the surface of the microfibers became smoother after long-term intensive abrasion (Fig. 3g-h). The stability of the HD-POS@PET fabric against tape peeling is shown in Fig. S8. The WSA deceased a little to 10° and the WRG decreased to 4 grades after 10 peeling cycles. 100 cycles later, the WSA was still around 15°, and the WRG was 3 grades, indicating high stability of the facric against tape peeling. Clothes are frequently deformed during body movements, and mechanical deformation often leads to micro-/nanostructure changes of superhydrophobic layers, resulting in deterioration or even loss of superhydrophobicty [66]. The WSA of the HDPOS@PET fabric kept below 8° with stretching strain up to 150%, and then gradually increased to ~15° when the strain was 300% (Fig. S9). Furthermore, the WSA remained at ~9° and the WRG kept at 4 grades after 1000 cycles of cyclic stretching-releasing at 100% strain (Fig. 3c). The retaining of superhydrophobicity at high strain and after cyclic stretching-releasing demonstrates excellent stretching durability of the fabric. The excellent mechanical durability of the HD-POS@PET fabric is owing to i) the hierarchical micro-/nanostructure formed by combination of microstructure of the PET fabric and nanostructure of the HD-POS layer, ii) stable bonding of HD-POS on the PET microfibers, and iii) inherent high stability and elasticity of HD-
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POS as a silicone material [67–69]. These are also responsible for the excellent environmental and chemical durability of the fabric as shown below. 3.4. Environmental and chemical robustness of HD-POS@PET fabrics The HD-POS@PET fabric did not show obvious change in the WSA and WRG after UV irradiation for 7 days (Fig. S10), ensuring long-term outdoor applications. The environmental robustness of the fabric was further tested by outdoor weathering (Fig. 3d). The superhydrophobicity kept unchanged until the snows on Dec. 28 and 31, which led to increase in the WSA to 15° and decrease of the WRG to 4 grades, which might because the surface was slightly contaminated by the impurities in the snows. The WSA gradually increased but the WRG unchanged with prolonged outdoor weathering. However, after 77 days, the superhydrophobicity was improved as the WSA decreased to 17°. This is ascribed to temperature rise in spring, leading to diffusion of HD-POS to the surface of the fabric to minimize the surface energy. Heat treatment can improve superhydrophobicity or superamphiphobicity by migration of silicone materials to the surface of damaged coatings [36,50]. Finally, the WSA was ~21° and the WRG was 3 grades after 117 days (on Apr. 21, 2019), indicating long-term durability of the fabric in outdoor conditions. Chemical durability of the HD-POS@PET fabric was evaluated by various approaches. After 7 days immersion in HCl solution (pH 1) or NaOH solution (pH 14), the WSA was ~ 8° and the WRG stayed at 4-5 grades (Fig. S11a). After 225 min in boiling water, the WSA was
Fig. 5. Digital images, infrared images and schematic illustrations of the boiling water scald models on rat dorsum covered by the (a-c) PET and (d-f) HD-POS@PET fabrics. The arrows in the infrared images show heads of the rats.
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~13° and the WRG stayed at 4 grades (Fig. S11b). The fabric also showed excellent thermostability up to 250 °C (Fig. S11c). Moreover, ultrasonic treatment in water or ethanol for 60 min resulted in negligible changes in the WSA and WRG (Fig. S11d). 3.5. HD-POS@PET fabrics for preventing scald To find out the difference between the PET and HD-POS@PET fabrics when contacting with boiling water, infrared camera and video camera were employed to record the process of pouring 100 mL of boiling water on the fabrics (20 20 cm) from both horizontal and vertical views (Fig. S2). From the horizontal view (Fig. 4a-b and Movie S5), all the hot water quickly wetted and penetrated the PET fabric. The water temperature at lower surface of the PET fabric was as high as 85.5 °C after 1.5 s and was still above 60 °C after 6 s. Hot water stayed in the fabric even after 9 s. From the vertical view (Fig. 4d-e and Movie S6), the water temperature at lower surface of the PET fabric was still above 70 °C after 9 s, and all the wetted area was at very high temperature. The high temperature area reached 2/3 of the fabric. A large amount of hot water above 70 °C with such long contact time and large contact area would cause serious scald. Differently, boiling water could not penetrate the HD-POS@PET fabric but rolled off the fabric from the edge (Movie S5). The hot water completely left the fabric in 3 s. Although the temperature at the lower surface of the HD-POS@PET fabric reached 80.4 °C after 1.5 s, the temperature dropped quickly to 60 °C in 2.7 s (Fig. 4a, c), which is much shorter than the minimum duration (5 s) to cause scald [1,3,6]. The temperature difference between the PET and HD-POS@PET fabrics could be seen more
clearly from the vertical view (Fig. 4d-f and Movie S6). The temperature dropped quickly to 60 °C in 3.2 s, to 39.2 °C in 4.5 s, and to room temperature in 8.0 s. Also, the high temperature area was no more than 1/2 of the fabric. The temperature increase at the lower surface of the HD-POS@PET fabric is attributed to heat conduction and radiation through the fabric as well as diffusion of a small amount of hot vapor [70]. The above results demonstrate that the HD-POS@PET fabric cools down much more quickly than the PET fabric by efficiently inhibiting hot water penetration, reducing contact time and contact area with hot water, and thus could probably be used for scald-preventing. The scald-preventing performance of the HD-POS@PET fabric was studied by a boiling water scald model on rats dorsum. Once encountering boiling water, the PET fabric was immediately wetted and the temperature at upper surface of the fabric sharply increased to ~89 °C after 1 s (Fig. 5a–c and S12a). All the hot water and most of the hot vapor penetrated the PET fabric and contacted with the skin. The temperature was still as high as 82 °C after 2 s and 58 °C after 9 s, which could still cause scald to the skin [4]. The temperature of the area between the fabric and the rats dorsum must be even higher due to slow heat conduction and radiation, condensation of hot vapor and hot water cooling. Differently, for the HD-POS@PET fabric, boiling water rapidly rolled off once contacting with the fabric (Fig. 5d–f and S12b), avoiding direct contact of hot water with rats dorsum and inhibiting penetration of most of hot vapor. Thus, the temperature at upper surface of the fabric increased to 77 °C after 1 s, but dropped quickly to ~64 °C after 2 s and to ~35 °C after 9 s owing to evidently reduced contact time and contact area with hot water.
Fig. 6. Digital images of rat dorsum and histology images of rat dorsum skin covered with the (a, b) PET and (c, d) HD-POS@PET fabrics after the scald test with (e, f) the control group for comparison.
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To evaluate the scald injuries, the changes of the dorsum skin were tracked for 48 h. At the moment after the scald test, the rats dorsum of all the three groups did not show visible difference. However, 6 h later, wound appeared on the rats dorsum covered with the PET fabric (Fig. 6a and S13a). The scald injury was very evident after 24 h, almost the same as 48 h later. The bottom side was bright-red due to loss of the epidermis, and the top part was pale and swollen. Then, the dorsum samples were cut, sectioned and observed by optical microscope (Fig. 6b and S13b). Some epidermis disappeared, pyknosis and extensive necrosis were observed in the keratinocyte nuclei (blue arrows), and the follicle-like structures were damaged (green arrows). These results indicate serious scald injury. However, the dorsum skin covered with the HD-POS@PET fabric did not show any evident difference in 48 h compared with the control group (Fig. 6c, e and S13c, e). The rats dorsum was even covered with new hairs after 48 h, indicating that the skin was healthy. From the dorsum skin histology images (Fig. 6d, f and S13d, f), no difference can be found between the HD-POS@PET fabric covered group and the control group, except that acidophilia of collagen decreased due to very slight edema in the corium (black arrows). Due to excellent hot water repellency and water impalement resistance, the HD-POS@PET fabric can (i) avoid direct contact of hot water and vapor with rat skin by preventing penetration of hot water and most of vapor, (ii) reduce heat conduction and radiation to rat skin by reducing contact time and contact area of hot water with the fabric. Consequently, the HD-POS@PET fabric kept dry and the temperature of the fabric in contact with the skin was much lower than that of the PET fabric once encountering hot water, ensuring efficient scald-preventing. 4. Conclusions In summary, we have demonstrated the creation of a robust HD-POS@PET fabric with excellent hot water repellency and water impalement resistance for efficient scald-preventing via a simple waterborne and nonfluorinated approach. The fabric features excellent hot water repellency even for dynamic boiling water and high water impalement resistance of 5 grades. Moreover, the fabric shows high mechanical, environmental and chemical robustness in various harsh conditions such as 200 cyles washing, 10,000 cycles abrasion, 100 cycles tape peeling, 1000 cycles 100% stretching and releasing, 168 h UV irradiation, 168 h corrosive liquids erosion and 117 days outdoor weathering, which is superior to most of previous studies [44,62]. These extraordinary properties are attributed to hierarchical micro-/nanostructure of the fabric, stable bonding of the compact HD-POS layer on the PET microfibers, and inherent high stability and elasticity of HD-POS as a silicone material. The fabric demonstrates efficient scald-preventing performance according to the simulation experiments. Hot water can completely leave the HD-POS@PET fabric in 3 s, and the surface temperature decreased to 60 °C 10 s quicker than the pristine fabric. Furthermore, the scald model on rats dorsum and histological analysis demonstrate that the rats covered with the pristine fabric was injuried seriouly, while those covered with the HD-POS@PET fabric were perfectly protected, reflecting that the HD-POS@PET fabric can indeed avoid direct contact of hot water and vapor with rat skin, and reduce heat conduction and radiation to rat skin. The biomimetic fabric might be used to avoid or at least alleviate most of scald injuries in our daily life rather than treatment after scald. CRediT authorship contribution statement Ning Tian: Conceptualization, Methodology, Investigation, Writing - original draft. Jinfei Wei: Methodology, Investigation.
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Yabin Li: Investigation, Data curation. Bucheng Li: Methodology, Investigation. Junping Zhang: Conceptualization, Supervision, Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This study was supported by the National Natural Science Foundation of China (51873220), and the Funds for Creative Research Groups of Gansu, China (17JR5RA306). Appendix A. Supplementary material Supplementary data to this article can be found online at https://doi.org/10.1016/j.jcis.2020.01.067. References [1] M. Stone, J. Ahmed, J. Evans, The continuing risk of domestic hot water scalds to the elderly, Burns 26 (2000) 347–350. [2] T.W. Chiu, D.C. Ng, A. Burd, Properties of matter matter in assessment of scald injuries, Burns 33 (2007) 185–188. [3] C. Loller, G.A. Buxton, T.L. Kerzmann, Hot soup! Correlating the severity of liquid scald burns to fluid and biomedical properties, Burns 42 (2016) 589– 597. [4] Y. Liu, X. Chen, J.H. Xin, Can superhydrophobic surfaces repel hot water?, J. Mater. Chem. 19 (2009) 5602. [5] M.H. Toon, D.M. Maybauer, L.L. Arceneaux, J.F. Fraser, W. Meyer, A. Runge, M.O. Maybauer, Children with burn injuries–assessment of trauma, neglect, violence and abuse, J. Inj. Violence Res. 3 (2011) 98–110. [6] E.M. Quist, M. Tanabe, J.E. Mansell, J.L. Edwards, A case series of thermal scald injuries in dogs exposed to hot water from garden hoses (garden hose scalding syndrome), Vet. Dermatol. 23 (2012) 162–166. e33. [7] M. Wu, B. Ma, T. Pan, S. Chen, J. Sun, Silver-nanoparticle-colored cotton fabrics with tunable colors and durable antibacterial and self-healing superhydrophobic properties, Adv. Funct. Mater. 26 (2016) 569–576. [8] H. Zhou, H. Wang, H. Niu, A. Gestos, X. Wang, T. Lin, Fluoroalkyl silane modified silicone rubber/nanoparticle composite: a super durable, robust superhydrophobic fabric coating, Adv. Mater. 24 (2012) 2409–2412. [9] B. Deng, R. Cai, Y. Yu, H. Jiang, C. Wang, J. Li, L. Li, M. Yu, J. Li, L. Xie, Laundering durability of superhydrophobic cotton fabric, Adv. Mater. 22 (2010) 5473– 5477. [10] Q. Zhu, Q. Gao, Y. Guo, C.Q. Yang, L. Shen, Modified silica sol coatings for highly hydrophobic cotton and polyester fabrics using a one-step procedure, Ind. Eng. Chem. Res. 50 (2011) 5881–5888. [11] Q. Ma, B. Wang, J. Xu, J. Lv, H. Li, Y. Li, C. Zhao, Preparation of superhydrophobic polyester fabric by growing polysiloxane microtube and its application, Silicon 10 (2018) 2009–2014. [12] B. Li, J. Zhang, Durable and self-healing superamphiphobic coatings repellent even to hot liquids, Chem. Commun. (Camb) 52 (2016) 2744–2747. [13] T. Mouterde, P. Lecointre, G. Lehoucq, A. Checco, C. Clanet, D. Quere, Two recipes for repelling hot water, Nat. Commun. 10 (2019) 1410. [14] M. Cao, X. Luo, H. Ren, J. Feng, Hot water-repellent and mechanically durable superhydrophobic mesh for oil/water separation, J. Colloid Interface Sci. 512 (2018) 567–574. [15] J. Zhang, B. Li, L. Wu, A. Wang, Facile preparation of durable and robust superhydrophobic textiles by dip coating in nanocomposite solution of organosilanes, Chem. Commun. (Camb) 49 (2013) 11509–11511. [16] C.-H. Xue, Y.-R. Li, J.-L. Hou, L. Zhang, J.-Z. Ma, S.-T. Jia, Self-roughened superhydrophobic coatings for continuous oil–water separation, J. Mater. Chem. A 3 (2015) 10248–10253. [17] Z. Du, P. Ding, X. Tai, Z. Pan, H. Yang, Facile preparation of Ag-coated superhydrophobic/superoleophilic mesh for efficient oil/water separation with excellent corrosion resistance, Langmuir 34 (2018) 6922–6929. [18] P. Raturi, K. Yadav, J.P. Singh, ZnO-nanowires-coated smart surface mesh with reversible wettability for efficient on-demand oil/water separation, ACS Appl. Mater. Interfaces 9 (2017) 6007–6013. [19] E.J. Falde, S.T. Yohe, Y.L. Colson, M.W. Grinstaff, Superhydrophobic materials for biomedical applications, Biomaterials 104 (2016) 87–103. [20] Z. Qin, J. Liu, X. Zeng, A simple way to achieve superhydrophobic surfaces with tunable water adhesion by a nanosecond pulse laser, SPIE/COS Photonics Asia 10813 (2018) 14.
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