One-Step Synthesis of Superhydrophobic Coating on Cotton Fabric by

Aug 29, 2013 - Superhydrophobic surfaces are highly hydrophobic; that is, they are extremely ... superhydrophobic textiles contain two-step coating pr...
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One-Step Synthesis of Superhydrophobic Coating on Cotton Fabric by Ultrasound Irradiation Mohammad E. Yazdanshenas* and Mohammad Shateri-Khalilabad* Department of Textile Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran S Supporting Information *

ABSTRACT: Superhydrophobic textiles are materials that have been treated to become resistant to penetration by water and wetting. Such materials have attracted substantial interest because of their high potential for applications in various areas. They are usually made in a two-step coating process: formation of nanoscale roughness on microscale fibers and subsequent hydrophobization by low-surface-energy materials. In this study, a facile one-step ultrasound-assisted approach was developed for the synthesis of silica nanoparticles (SiNPs) functionalized with octyltriethoxysilane and their in situ incorporation into cotton fabrics. The fabrics were tested in terms of water contact angle (CA) and water shedding angle (SHA) and were characterized by SEM, EDX and FTIR spectroscopies, and reflectance spectrophotometry. SEM and AFM images revealed that the functionalized SiNPs formed a nearly close-packed assembly on the fibers and increased the roughness value of the fabric. The fabric showed stable superhydrophobicity with CA and SHA values of 152.8° ± 2.6° and 8°, respectively. Reflectance spectra showed that the coating was transparent and could not affect the color of the fabric. In addition, the coating had high stability against repeated washing, and its mechanical properties were not substantially affected.

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INTRODUCTION Superhydrophobic surfaces are highly hydrophobic; that is, they are extremely difficult to wet and have contact angles (CA) of greater than 150°. Inspired by the special surface structure of lotus leaf, many researchers have prepared a variety functional superhydrophobic surfaces during the past two decades.1−4 Active studies on superhydrophobic materials have eventually led to industrial applications. Because textile materials have diverse applications in various industries, interest in superhydrophobic textiles has increased greatly. Superhydrophobic textiles have applications such as self-cleaning, water-proof, and soil-repellent apparel; oil/water separation filters; and microfluidic channels.5−12 The wetting behavior of a solid surface is controlled by both the geometric structure and the chemical composition of the material. Generally, for the conversion of a hydrophilic substrate into a superhydrophobic surface, two key parameters are essential: creation of hierarchical surface structures (microscale roughness covered by nanoscale roughness or micro-/nanoscale roughness) and a low-surface-energy layer. Because textiles are constructed from interlacing yarns with microscale fibers, they naturally have a microscale structure, and further nanoscale coatings and low-surface-energy layers are needed for their conversion into superhydrophobic surfaces. According to this principle, various superhydrophobic textiles have been successfully prepared using nanoparticles, especially inorganic nanoparticles comprising SiO2, ZnO, CuO, Ag, Au, CeO2, and TiO2, combined with low-surface-energy material coatings such as alkylsilanes.5−21 The most widely used strategies for the fabrication of superhydrophobic textiles contain two-step coating processes, and only a few works have been reported for the fabrication of these surfaces in one step. For example, there are reports of the formation of superhydrophobic polymethylsiloxane nanostruc© 2013 American Chemical Society

tures on the surface of cotton fabrics using methyltrichlorosilane in a one-step solution immersion process.22−24 However, the problem with this approach is the formation of hydrochloric acid during the coating process, which causes damage to the acid-sensitive cotton cellulose fibers (instability of β-acetal bonds in acidic solutions) and, therefore, reduces the mechanical properties of the treated cotton textiles. In another report, Pereira et al. described an effective method for the preparation of cotton fabric with superamphiphobic properties by synthesizing mesoporous silica nanoparticles (SiNPs) functionalized with tridecafluorooctyltriethoxysilane and incorporating them into cotton textiles using a one-pot cocondensation methodology.5 In this study, a sonochemistry method was used for the onestep synthesis of superhydrophobic coating on cotton fabric. The reaction was performed by transferring fabric into a solution containing the nanoparticles and low-surface-energy forming materials, namely, tetraethylorthosilicate (TEOS) and octyltriethoxysilane (OTES). Using this simple method, SiNPs functionalized with OTES were deposited on the fabric in situ, resulting in a surface structure similar to that of the lotus leaf. As a consequence, the superhydrophilic cotton fabric became a superhydrophobic substrate.

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EXPERIMENTAL SECTION Materials. Tetraethylorthosilicate (TEOS), n-octyltriethoxysilane (OTES), and ammonia solution (25%) were purchased from Merck. Ethanol (96%) was supplied by Razi Chemical Co., Tehran, Iran. Commercial 100% cotton fabric (twill weave, Received: Revised: Accepted: Published: 12846

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330 g/m2) was obtained from Yazdbaf Textiles Co., Yazd, Iran. The fabric was desized, scoured, and bleached before being used. Coating Process. TEOS and OTES (100 μL each) were added under magnetic stirring to a beaker containing 50 mL of ethanol. One gram of cotton fabric (3 × 9 cm) was transferred to this solution and left to be stirred for 2 min. Then, 500 μL of ammonia solution was added, and the mixture was transferred to an ultrasonic bath. It was kept under ultrasound irradiation using a Euronda bath sonicator (Eurosonic 4D, 50/60 Hz) with a power of 350 W for 60 min. According to the supplier, the working frequency of this instrument is 34−37 kHz. During irradiation, the temperature of the reaction mixture increased from 26 to 45 °C. At the end of the reaction, the fabric was removed from the solution, washed several times with water, and then dried and cured at 120 °C for 60 min. For comparison, two reference samples were also prepared, one by reaction of the fabric with only OTES and the other by reaction with OTES−TEOS under magnetic stirring without sonication, to highlight the effects of the preparation conditions on the wetting properties of the fabric. Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy. Microscopic investigations of the specimens were carried out using an AIS-2100 scanning electron microscope (SEM). The specimens were mounted on conductive carbon adhesive tabs and images were taken after the specimens had been sputter-coated (SC 7620 EMITECH) with a very thin layer of gold. To determine the elemental composition of the fabric surface, an energy-dispersive X-ray (EDX) detector was used with a VEGA TS 5136XM scanning electron microscope. Atomic Force Microscopy. Atomic force microscopy (AFM) images were obtained in ac mode using a Dualscope/ Rasterscope C26 (Danish Micro Engineering A/S, Copenhagen, Denmark). The root-mean-square (RMS) roughness of the fabrics was measured from the mean plane and determined according to 3 × 3 μm scans. Fourier-Transform Infrared Spectroscopy. Fouriertransform infrared (FTIR) spectra of the fabrics were obtained by the KBr pellet technique. Fine fibers of the samples were collected by manual abrasion. The obtained fibers were ground and dispersed in a matrix of KBr by glass mortar. The pellets were then formed by compression at 7 t for 30 s. FTIR spectra were recorded on a Bruker Tensor 27 FTIR spectrometer. The spectra were recorded in the wavelength range of 4000−400 cm−1 at ambient temperature. Thermogravimetric Analysis. Thermograms of the fabrics were obtained on a TA Instruments model TGA Q50 apparatus under argon flow (60.0 mL/min) at a heating rate of 20 °C min−1 from 30 to 600 °C. Water Contact Angle. Static water contact angle (CA) measurements were completed on a self-developed goniometer apparatus coupled to a high-resolution camera based on previous work.25 Distilled water droplets with a volume of 5 μL were carefully dispensed from a syringe onto the fabric (3 × 3 cm) surface. The water CA was measured 60 s after the droplets were placed on a fabric sample’s surface. For statistics, four separate measurements were performed in different locations on the fabric surface, and the results were averaged to obtain the mean and standard deviation. Water Shedding Angle. Water shedding angle (SHA) measurements were determined according to the method of Zimmermann et al.26 Briefly, the fabric (3 × 3 cm) sample was

attached to a glass coverslip with double-sided adhesive tape and placed on a custom-built tilting table. A syringe containing distilled water was mounted above the tilting table with a fixed 2-cm needle-to-substrate distance. Droplets of water (5 μL) were released onto the samples at a minimum of four different positions, each 2 cm from the bottom end of the sample. The lowest inclination angle at which all of the droplets completely rolled or bounced off the surface was noted as the SHA. Water Repellency. The water repellency of the modified fabrics was evaluated according to AATCC test method 1932005.27 This test method evaluated the fabric’s resistance to wetting using a selected series of eight water/isopropyl alcohol solutions of different surface tensions. Drops (50 μL) of standard test liquids were placed on the fabric (3 × 3 cm) surface in three locations and observed for wetting and wicking at a 45° angle. The aqueous repellency grade was the number corresponding to the highest-numbered test liquid that did not penetrate or wet the fabric surface at the liquid−fabric interface and for which no wicking occurred around the drops within 10 ± 2 s. Transmittance/Reflectance Spectra and Color Measurements. Transmittance/reflectance spectra of the fabric samples (3 × 3 cm) were determined using a Perkin-Elmer Lambda 35 UV−vis spectrophotometer. The spectra were recorded in the range of 400−700 nm. Air was used as the reference. The three coordinates (L*, a*, and b*) of the CIELAB color system and the color difference (ΔE) of the fabrics were measured by colorimetry software. The measurements were performed under standard illuminant D65 and at a 10° observing angle. Washing Durability. The treated cotton fabrics were washed with other loading fabrics to obtain sufficient rubbing and reflect true washing durability under normal conditions. The samples were washed according to ISO method 105C10:2006(C) with 5 g L−1 nonionic soap solution (with a liquor ratio of 50:1) at 50 °C for 45 min. The samples were rinsed in cold distilled water, held under cold tap water for 10 min, dried at room temperature, and heat-treated in an oven at 110 °C for 60 min. The samples were washed for 1, 5, 10, and 15 cycles. Fabric Thickness. The thickness of the fabrics was measured using a Uni-thickness measuring device. Measurements were carried out on samples of fabric with a 5-cm diameter at a pressure of 20 kPa. The reported values represent the means of four measurements each. Bending Modulus. The bending modulus of the fabrics was measured by the cantilever method using a stiffness tester. The bending modulus Q (in g/cm2) is given by the equation Q=

12G × 10−3 g3

where g is fabric thickness (in cm). G is the flexural rigidity, which is calculated as G = 0.1MC 3

where M is the mass per unit area of the fabric (in g/m2) and C is the bending length (in cm). The reported values of bending modulus represent the means of four measurements each. Air Permeability. Air permeability was examined with a Metefcm air permeability tester. The dimension of the used fabrics was 9 × 9 cm. The reported values represent the means of four measurements each. 12847

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Figure 1. Schematic illustration of chemical structures and coating procedure for the fabrication of superhydrophoic cotton fabric.

Figure 2. SEM images of (a) pristine and (b) OTES−TEOS-treated cotton fabrics. Images on the right are at higher magnification.

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RESULTS AND DISCUSSION

the surface into the pore or channels, instead of being embedded in the wall of the silica matrix. The sonochemical irradiation of a liquid causes two primary effects, namely, cavitation (bubble formation, growth, and collapse) and heating. When the microscopic cavitation bubbles collapsed near the surface of the fabric, they generated powerful shock waves and microjets that caused effective stirring/mixing of the adjusted layer of the liquid. The later effects of cavitation are several hundred times greater in heterogeneous than homogeneous systems. In the reaction vessel, the ultrasonic waves promoted fast migration of the newly formed hybrid SiNPs to the fabric’s surface. This might cause local melting of the fibers at the contact sites, which might be the reason for the particles’ strong adherence to the fabric. The surface morphologies of the pristine and OTES−TEOStreated fabrics were investigated by electron microscopy. The corresponding scanning electron microscopy (SEM) images are shown in Figure 2. The low-magnification images show that the treated fabric looked similar to the untreated one. The high-

The chemical structures and methodology used to prepare superhydrophobic coating on cotton fabric are presented in Figure 1. Hydrophobic SiNPs were synthesized in situ on the cotton surface by hydrolysis and condensation of TEOS under alkaline conditions in the presence of OTES under ultrasonic irradiation. The hybrid SiNPs produced by this reaction were thrown onto the surface of the cotton fibers by sonochemical microjets resulting from the collapse of sonochemical bubbles.28 As the hydrolysis rate of TEOS is relatively higher than that of organically modified siloxanes, the sol−gel reaction proceeded in stepwise fashion. That is, TEOS was hydrolyzed and condensed first to form the silica matrix, whereas OTES was subsequently hydrolyzed and co-condensed on the preformed silica network surface, which suggests that the organic groups were located on the inner surface of the silica matrix; in other words, the functional groups protruded from 12848

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Figure 3. AFM images of (a) pristine and (b) OTES−TEOS-treated cotton fibers.

Figure 4. EDX spectra of (a) pristine and (b) OTES−TEOS-treated cotton fabrics.

provided a large degree of roughness to the fibers’ top surfaces and imparted nanoscale surface roughness. It is obvious that the SiNPs coated on the cotton fabric were random and close-

magnification images reveal a smooth longitudinal fibril structure of the pristine cotton fibers, whereas the treated cotton fibers were coated with tiny SiNPs. The coating 12849

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the treated sample (Figure 4b) exhibits a new absorption band at 795 cm−1 corresponding to Si−C stretching. Also, the new band at 2830 cm−1 and the increased band intensity at 2900 cm−1 of −CH2 due to C−H symmetric and asymmetric stretching, respectively, indicate the introduction of long-chain hydrocarbons. However, the typical absorption of the Si−O−Si bands of OTES−SiNPs in the 1100−1000 cm−1 region appears to be overlapped by cellulose bands due to C−O bending modes. Furthermore, significant reductions of the OH stretching band around 3315 cm−1 and the OH bending band at around 1635 cm−1 were observed, which confirms the moisture reduction of the treated fabric. These results confirm the successful reaction of the cotton cellulose with OTES− TEOS and formation of Si−O−Si bonds on the coating surface, which contributed to the lower surface energy. The wettability properties of the fabrics were evaluated by water CA and SHA measurements. Pristine cotton fabric demonstrated superhydrophilic behavior due to the presence of abundant hydroxyl groups on the surface of their cellulose fibers, so that water droplets were quickly absorbed and disappeared on its surface, as seen in Figure 6a. The OTES− TEOS-treated fabric exhibited superhydrophobic behavior with a CA of 152.8° ± 2.6° (Figure 6b) and an SHA of 8°. Droplets of water that fell on the superhydrophobic fabric formed highly spherical beads that stood up on the surface and easily rolled off, effectively making the surface waterproof. In addition, the repellency was stable, and the droplets were not adsorbed after a long time until complete evaporation. For comparison, the wettability properties of fabric treated with only OTES and fabric treated with OTES−TEOS (in the absence of sonication) were evaluated. In both cases, weak hydrophobicity was observed, so that the droplets were adsorbed and disappeared in less than 10 s, which demonstrates both the substantial effect of sonication and the synergetic effect of OTES and TEOS in obtaining superhydrophobic fabric. The water repellency of the prepared superhydrophobic fabric was also determined according to AATCC test method 193-2005. The obtained results demonstrated a reduction of the surface tension of the fabric so that it gained a rating of 3, that is, able to repel liquid with a surface tension of greater than 42 dyn/cm. Generally, two crucial factors govern surface wetting behavior. One is surface roughness, represented by various periodically or randomly distributed hierarchical structures, and the other is the surface chemical composition. Cotton fabric is a rough, porous substrate produced by interlacing threads (composed of micrometer-sized cellulose fibers) and placed perpendicular to each other. Consequently, microscale roughness is naturally provided, and further nanoscale roughness is necessary for the formation of a dual-scale structure. In addition, a low-surface-energy coating is needed for conversion into a superhydrophobic substrate. Here, as shown in SEM images, nanoscale roughness and low-surface-energy layer were obtained through the formation of hybrid hydrophobic SiNPs. As a consequence, a superhydrophobic cotton fabric with a dual-scale surface structure was formed. The prepared superhydrophobic fabric was highly waterrepellent and stayed afloat on water. After being forced under water, a layer of silver sheen covered the whole fabric due to total reflectance of light at the air layer trapped on the fabric surface, defined as a plastron layer. This behavior is evident in Figure 7, which shows photographs of the pristine and OTES−

packed, which caused complete surface coverage of the cellulose fibers. An SEM survey of 50 isolated particles confirmed the average size of the particles as 88 nm. Also, the SEM image of the OTES−TEOS-treated fabric without sonication was obtained (Figure S1, Supporting Information). It was observed that the particles were inhomogenously distributed on the fibers’ surface and many particles were agglomerated. This result demonstrates the effective role of sonication in the formation of homogeneous particles on the fibers. Atomic force microscopy (AFM) images also revealed the nanoscale roughness of the surface coating (Figure 3). Based on the AFM images, the root-mean-square (RMS) roughness of the fabrics was measured. The cotton fibers of the pristine fabric had an RMS roughness of 38.5 nm (Figure 3a), whereas the fibers after OTES−TEOS coating had an RMS roughness of 77.2 nm (Figure 3b). Thermogravimetric analysis (TGA) was used to determine the remaining weight of pristine and OTES−TEOS-treated cotton fabrics. As shown in Figure S2 (Supporting Information), for the pristine cotton, the remaining weight percentage was 5.9%. After the hybrid SiNPs had been grafted onto the cotton fibers, this percentage increased to 6.0%. The very low difference in the weights of the samples could be due to the low SiNP content of the treated fabric, as demonstrated by EDX spectroscopy (discussed next). The chemical composition of the surface of the fabrics was analyzed by EDX spectroscopy (Figure 4). The spectrum of the pristine sample showed peaks for carbon and oxygen, but no silicon was detected. However, the EDX spectrum of the coated sample yielded carbon, oxygen, and silicon peaks. For the coated fabric, the weight percentage of silicon was 0.67%. The presence of the silicon peak indicates the successful formation of hybrid OTES−SiNPs on the surface of the treated fabric. To further corroborate the different surface chemical compositions of the fabrics, FTIR spectroscopy was used to characterize the species introduced onto the fabrics’ surface. Figure 5 shows FTIR spectra of the pristine and OTES−TEOStreated samples. The FTIR spectra of both samples show characteristic bands for cellulose: OH stretching at ca. 3500− 3000 cm−1, CH stretching at 2900 cm−1, OH bending at 1635 cm−1, CH2 bending at 1430 cm−1, CH bending at 1380 cm−1, C−O stretching at 1058 and 1035 cm−1, and CH bending or CH2 stretching at 900 cm−1. In addition, the FTIR spectrum of

Figure 5. FTIR spectra of (a) pristine and (b) OTES−TEOS-treated fabrics. 12850

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Figure 6. Colored water droplets sitting on (a) pristine and (b) OTES−TEOS-treated cotton fabrics. Goniometer images for 5-μL droplets are shown on the right.

Figure 7. Photographs of pieces of (a) pristine and (b) OTES−SiNP-treated cotton fabrics immersed in water.

TEOS-treated fabrics in water. Although the striped weave pattern of the fabric is discernible for the pristine cotton, this pattern cannot be seen for the submerged coated fabric because of the light reflection by the plastron layer. More interestingly, this plastron layer was retained after the fabric was submerged in water for a long time. After removal from water, the fabric was not soaked or wetted by the liquid, although some drops remained adhered to the fabric. These observations are consistent with the findings of Nosonovskii ̆ and Bhushan, who showed that a dual-scale structure was not only necessary for a high CA but essential for the stability of the water−solid and water−air interfaces (the composite interface).29 On the basis of classical theories, there are two situations in the wetting of a rough surface: a homogeneous interface without any air pockets (Wenzel’s state)30 and a composite interface with air pockets trapped between the rough details (Cassie’s state).31 Experimentally, the wettability state can be distinguished by the presence or absence of light between liquid and substrate in a microscopic side view. Because cotton fabrics are porous substrates, they are considered physically heterogeneous (air pockets at the interface), irrespective of their different roughness scales. Thus, the observed superhydrophobic behavior was expected to be modeled by Cassie’s equation, which assumes that a liquid does not completely wet the rough hydrophobic surface because of the presence of air pockets

(composite surface) on the liquid−solid interface. The equation for Cassie’s state is cos θr = f1 cos θ − f2

(1)

where θr is the observed water CA on a rough, porous surface; θ is the intrinsic water CA on the corresponding smooth surface (θ = 93.2° for the smooth OTES surface);32 f1 is the liquid/solid contact area divided by the projected area; and f 2 is the liquid/vapor contact area divided by the projected area (f1 + f 2 = 1). According to this equation, the f 2 value of the treated fabric was 0.89, which indicates that the achievement of superhydrophobicity was the main result of air trapped in the very rough surface of the dual-scale OTES−TEOS-treated fabric. The very low SHA of the fabric can be attributed to the complete surface coverage of the cotton fibers with very rough hydrophobized SiNPs.23 In addition to achieving superhydrophobicity in one step, the superhydrophobic coating obtained was highly transparent: The fabric weaving pattern can be clearly seen through the blue-colored superhydrophobic fabric (Figure 8, photographs). The high optical transparency was further supported by the UV−visible transmittance spectra (Figure 8). Compared to the pristine blue-colored cotton, the treated fabric showed the same transmittance in the range of 400−700 nm, which demonstrates a nearly invisible coating. 12851

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Figure 8. Transmittance spectra of blue-colored fabric (a) before and (b) after OTES−TEOS coating.

Also, to assess the effect of the coating on the color of the fabric, reflectance spectra were recorded (Figure S3, Supporting Information). The spectra showed a small increase in the reflectance percentage of the treated fabric in comparison to that of the pristine blue-colored fabric. The CIE L*, a*, and b* values, quantitatively characterizing the color of the samples, are reported in Table S1 (Supporting Information). The colorimetric measurements reveal a small total color difference (ΔE) between the two samples. It is worth noting that the total color difference of ΔE = 2 corresponds to a difference that is just noticeable by eye. To evaluate the washing durability, the fabric was washed for 1, 5, 10, and 15 cycles according to ISO test method 105C10:2006(C). Figure 9 shows the effects of repeated washings on the CA and SHA. With increasing washing up to 10 cycles, the coated fabric had a small decrease in CA. However, after 15

cycles of washing, a decrease of about 10° was observed in the CA. Nevertheless, the CA remained above the 130° threshold for ultrahydrophobic surfaces. It should be noted that the droplets sitting on all of the samples were stable and could not be adsorbed after a long time. Figure 9 also shows that the SHA did not change for the samples washed for 1 and 5 cycles. Most of the increase in the SHA occurred after 10 and 15 washing cycles, after which the SHA increased to 21 and 25, respectively, and demonstrated an increase in the stickiness of the droplets to the fabric surface. This observation is presumably due to the removal of some hydrophobized SiNPs from the coating layer during washing, as demonstrated in SEM images (Figure S4, Supporting Information). However, the results showed a high washing durability of the superhydrophobic coating formed on the fabric. The mechanical properties (tensile strength and elongation) of the pristine and superhydrophobic cotton samples were measured and compared to determine whether the coating process weakened the textile (Figure 10). The results show that the coating treatment of the fabric caused an approximately 9% decrease in tensile strength. However, the elongation was not affected. Consequently, the mechanical properties of the superhydrophobic fabric were comparable to those of the pristine fabric and were retained for practical applications. This coating also showed little influence on the handling properties of the fabric. The coating treatment slightly increased the fabric thickness from 0.582 to 0.586 mm. The bending modulus of fabric is an indication of the intrinsic stiffness of the fabric. The higher the bending modulus, the more rigid the fabric, and the less comfortable the fabric would be to wear. After the coating treatment, the bending modulus of the fabric increased from 37.8 to 42.4 kg/cm2, indicating that the superhydrophobic coating had a slightly negative influence

Figure 9. Effect of washing cycles on the CA and SHA of OTES− TEOS-treated fabric. 12852

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(3) Yao, X.; Song, Y.; Jiang, L. Applications of Bio-Inspired Special Wettable Surfaces. Adv. Mater. 2011, 23, 719. (4) Ionov, L.; Synytska, A. Self-Healing Superhydrophobic Materials. Phys. Chem. Chem. Phys. 2012, 14, 10497. (5) Pereira, C.; Alves, C.; Monteiro, A.; Magen, C.; Pereira, A. M.; Ibarra, A.; Ibarra, M. R.; Tavares, P. B.; Araujo, J. P.; Blanco, G.; Pintado, J. M.; Carvalho, A. P.; Pires, J.; Pereira, M. F.; Freire, C. Designing Novel Hybrid Materials by One-Pot Co-Condensation: From Hydrophobic Mesoporous Silica Nanoparticles to Superamphiphobic Cotton Textiles. ACS Appl. Mater. Interfaces 2011, 3, 2289. (6) Zhou, H.; Wang, H.; Niu, H.; Gestos, A.; Lin, T. Robust, SelfHealing Superamphiphobic Fabrics Prepared by Two-Step Coating of Fluoro-Containing Polymer, Fluoroalkyl Silane, and Modified Silica Nanoparticles. Adv. Funct. Mater. 2013, 23, 1664. (7) Synytska, A.; Khanum, R.; Ionov, L.; Cherif, C.; Bellmann, C. Water-Repellent Textile via Decorating Fibers with Amphiphilic Janus Particles. ACS Appl. Mater. Interfaces 2011, 3, 1216. (8) Zhou, H.; Wang, H.; Niu, H.; Gestos, A.; Wang, X.; Lin, T. Fluoroalkyl Silane Modified Silicone Rubber/Nanoparticle Composite: A Super Durable, Robust Superhydrophobic Fabric Coating. Adv. Mater. 2012, 24, 2409. (9) Yang, J.; Zhang, Z.; Men, X.; Xu, X.; Zhu, X.; Zhou, X. Counterion Exchange to Achieve Reversibly Switchable Hydrophobicity and Oleophobicity on Fabrics. Langmuir 2011, 27, 7357. (10) Owens, T. L.; Leisen, J.; Beckham, H. W.; Breedveld, V. Control of Microfluidic Flow in Amphiphilic Fabrics. ACS Appl. Mater. Interfaces 2011, 3, 3796. (11) Li, J.; Shi, L.; Chen, Y.; Zhang, Y.; Guo, Z.; Su, B.-l.; Liu, W. Stable Superhydrophobic Coatings from Thiol-Ligand Nanocrystals and Their Application in Oil/Water Separation. J. Mater. Chem. 2012, 22, 9774. (12) Basu, M.; Sinha, A. K.; Pradhan, M.; Sarkar, S.; Negishi, Y.; Pal, T. Fabrication and Functionalization of CuO for Tuning Superhydrophobic Thin Film and Cotton Wool. J. Phys. Chem. C 2011, 115, 20953. (13) Zhu, Q.; Gao, Q.; Guo, Y.; Yang, C. Q.; Shen, L. Modified Silica Sol Coatings for Highly Hydrophobic Cotton and Polyester Fabrics Using a One-Step Procedure. Ind. Eng. Chem. Res. 2011, 50, 5881. (14) Duan, W.; Xie, A.; Shen, Y.; Wang, X.; Wang, F.; Zhang, Y.; Li, J. Fabrication of Superhydrophobic Cotton Fabrics with UV Protection Based on CeO2 Particles. Ind. Eng. Chem. Res. 2011, 50, 4441. (15) Gao, Q.; Zhu, Q.; Guo, Y.; Yang, C. Q. Formation of Highly Hydrophobic Surfaces on Cotton and Polyester Fabrics Using Silica Sol Nanoparticles and Nonfluorinated Alkylsilane. Ind. Eng. Chem. Res. 2009, 48, 9797. (16) Shateri Khalil-Abad, M.; Yazdanshenas, M. E. Superhydrophobic Antibacterial Cotton Textiles. J. Colloid Interface Sci. 2010, 351, 293. (17) Chen, X.; Liu, Y.; Lu, H.; Yang, H.; Zhou, X.; Xin, J. H. In-Situ Growth of Silica Nanoparticles on Cellulose and Application of Hierarchical Structure in Biomimetic Hydrophobicity. Cellulose 2010, 17, 1103. (18) Lee, M.; Kwak, G.; Yong, K. Wettability Control of ZnO Nanoparticles for Universal Applications. ACS Appl. Mater. Interfaces 2011, 3, 3350. (19) Wang, T.; Hu, X.; Dong, S. A General Route to Transform Normal Hydrophilic Cloths into Superhydrophobic Surfaces. Chem. Commun. 2007, 1849. (20) Wang, L.; Zhang, X.; Li, B.; Sun, P.; Yang, J.; Xu, H.; Liu, Y. Superhydrophobic and Ultraviolet-Blocking Cotton Textiles. ACS Appl. Mater. Interfaces 2011, 3, 1277. (21) Roe, B.; Kotek, R.; Zhang, X. Durable Hydrophobic Cotton Surfaces Prepared Using Silica Nanoparticles and Multifunctional Silanes. J. Text. Inst. 2012, 103, 385. (22) Shirgholami, M. A.; Khalil-Abad, M. S.; Khajavi, R.; Yazdanshenas, M. E. Fabrication of Superhydrophobic Polymethylsilsesquioxane Nanostructures on Cotton Textiles by a SolutionImmersion Process. J. Colloid Interface Sci. 2011, 359, 530.

Figure 10. Mechanical properties of pristine and OTES−TEOStreated fabrics.

on the fabric handling. The air permeability decreased only slightly after coating from 24.1 to 23.4 m3/32/h.

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CONCLUSIONS Superhydrophobic cotton fabric was prepared by the facile onestep ultrasound-assisted synthesis of hydrophobic nanoscale roughness. The reaction of organic−inorganic hybrid precursors OTES and TEOS under ultrasonic irradiation was found to provide an effective superhydrophobic coating. The fabric showed superhydrophobicity with a water contact angle higher than 150° and a shedding angle of 8°. The enhanced surface roughness imparted by the SiNPs and the reduction of the surface free energy induced by the hydrophobic silane were responsible for the water repellency properties of the treated fabric. The application procedure did not significantly affect the physical and mechanical properties of the treated fabric. In addition, the superhydrophobicity was stable even after several washing cycles.

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ASSOCIATED CONTENT

S Supporting Information *

SEM images of the treated sample in the absence of ultrasonic irradiation, TGA curves, reflectance spectra, SEM images of a treated sample after 15 cycles of washing, and color coordinates/color differences of the fabric before and after treatment. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Tel.: +982188741057. *E-mail: [email protected]. Tel.: +989137075734. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research project was financially supported by the Research Council of the Yazd Branch, Islamic Azad University. REFERENCES

(1) Zhang, Y.-L.; Xia, H.; Kim, E.; Sun, H.-B. Recent Developments in Superhydrophobic Surfaces with Unique Structural and Functional Properties. Soft Matter 2012, 8, 11217. (2) Shirtcliffe, N. J.; McHale, G.; Atherton, S.; Newton, M. I. An Introduction to Superhydrophobicity. Adv. Colloid Interface Sci. 2010, 161, 124. 12853

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dx.doi.org/10.1021/ie401133q | Ind. Eng. Chem. Res. 2013, 52, 12846−12854