Materials Letters 255 (2019) 126562 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue A new method to prepare superhydrophobic cotton fabrics by post-coating surface modification of ZnO nanoparticles Gajanan D. Patil a,1, Aravind H. Patil a,b,1, Sushilkumar A. Jadhav a,⇑, Chetan R. Patil a, Pramod S. Patil a,b a b School of Nanoscience and Technology, Shivaji University, Kolhapur, Vidyanagar, 416004 Kolhapur, Maharashtra, India Department of Physics, Shivaji University, Kolhapur, Vidyanagar, 416004 Kolhapur, Maharashtra, India a r t i c l e i n f o Article history: Received 16 July 2019 Received in revised form 18 August 2019 Accepted 19 August 2019 Available online 20 August 2019 Keywords: ZnO nanoparticles Cotton fabrics Polymeric composites Surfaces Superhydrophobic cotton a b s t r a c t A new, simple and low cost method for the preparation of superhydrophobic cotton fabric by postcoating surface modification of zinc oxide nanoparticles (ZnO NPs) is developed. The method includes synthesis of ZnO NPs, their coating on fabric by padding dry cure technique and post deposition surface modification of the nanoparticles and of the fabric with hexadecyltrimethoxysilane (HDMS). The synthesized ZnO NPs and surface modified cotton fabrics were fully characterized. The ZnO coated and HDMS modified cotton fabric showed very high water contact angle of 152°. The high contact angle was maintained even after several washing cycles. Ó 2019 Elsevier B.V. All rights reserved. 1. Introduction The excellent water repellent ability of the lotus called ‘‘lotus effect’’ has attracted great attention in the past decades [1–4]. Numerous studies have been done to find out the physical and chemical mechanisms of that effect and mimic it by producing synthetic superhydrophobic materials. The superhydrophobic surfaces or materials are those which show water contact angle greater than 150° [5,6]. The cotton fabrics are widely used in daily life because of their excellent properties such as softness, comfort, biodegradation etc [7,8]. The large number of hydroxyl groups on its surface make cotton based textiles highly hydrophilic in nature [9]. Recently, nanotechnology in textiles has established a new way to obtain textiles with desirable properties such as hydrophobicity. This is achieved by coating the textiles with metal oxide nanoparticles which modifies the surface without losing intrinsic properties of the textile substrate [10]. Zinc oxide (ZnO) nanostructures are widely used for the preparation of textiles with hydrophobic and antimicrobial properties [11–14]. The permanent coating of the ZnO particles on the textile is important so that the particles will stay on the substrate during repeated laundry cycles. Although attempts were made to coat ZnO particles on the textiles, the coating was weak or the interactions ⇑ Corresponding author. 1 E-mail address: sushil.unige@gmail.com (S.A. Jadhav). GDP and AHP contributed equally to the work therefore both are lead authors. https://doi.org/10.1016/j.matlet.2019.126562 0167-577X/Ó 2019 Elsevier B.V. All rights reserved. were unstable in washing conditions. Therefore, as a significant new development towards the preparation of durable superhydrophobic cotton fabrics with embedded ZnO nanoparticles in the present work we have developed a simple and low cost method for the preparation of superhydrophobic cotton fabric by postcoating modification of ZnO NPs and of the cotton fabrics with hexadecyltrimethoxysilane (HDMS). Due to its compatibility with the industrial process the method can be easily transferred in an industrial set-up for superhydrophobic textile production. 2. Experimental 2.1. Materials Zinc acetate dihydrate (99.5%), polyethylene glycol (PEG), ammonia 25% and HDMS were purchased from Molychem India. The cotton fabrics were provided by D.K.T.E. Society Ichalkaranji, Maharashtra India’s textile engineering division. 2.2. Instruments and methods XRD patterns were recorded on Bruker D2 Phaser diffractometer. The UV–visible spectra were registered on Cary-60 UV/Visible spectrophotometer. ATR-FTIR spectra were recorded with Perkin Elmer spectrometer. The SEM images were taken on JEOL-JSM6360 from Jeol Ltd. Japan. The water contact angles were measured on Holmarc contact meter model HO-IAD-CAM-01B. 2 G.D. Patil et al. / Materials Letters 255 (2019) 126562 2.3. Synthesis of ZnO NPs, coating and modification 2.3.1. Synthesis of ZnO NPs Zinc acetate (4.38 g) and PEG (0.5 g) were solubilized in 200 ml water with vigorous stirring. Later, 200 ml of 25% ammonia was added to it with constant stirring. The reaction was allowed to proceed for 5 h and the pH of the solution was maintained around 8–9. After completion of the reaction the supernatant liquid was discarded. The remaining suspension was centrifuged and the obtained nanoparticles were washed and dried at 80 °C for overnight. The resulting powder was annealed at 400 °C for 2 h. 2.3.2. Coating of ZnO NPs The cotton fabric was cut in to 15 15 cm size piece and was immersed in the solution containing ZnO (1%) and acrylic binder (1%) for 15 min and then it was passed through a padding mangle. A 100% wet pick-up was maintained for all the treatments. After padding, the fabric was air-dried and then cured for 3 to 4 min at 140 °C. 2.3.3. Surface modification The ZnO NPs coated cotton fabrics were surface treated by applying HDMS. In this step, the ZnO coated fabric sample was immersed in HDMS solution (3.5 wt%) in ethanol and stored and room temperature for 24 h. The fabric sample was then washed with ethanol several times. It was then dried in air for prolonged time. 3. Results and discussion The process of the preparation of the superhydrophobic cotton fabrics with the developed method is shown in Fig. 1. The XRD spectrum of ZnO-NPs is shown in Fig. 2A. The peaks at 2h = 31.8, 34.2, 36.2, 47.6, 56.7, 62.7 and 67.99° of ZnO nanoparticles are corresponding to the growth of ZnO nanocrystallites along (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3) ,(2 0 0) (1 1 2 )and (2 0 2) orientations (JCPDS No. 01-089-7102). All the diffraction peaks can be indexed to the hexagonal wurtzite structured ZnO NPs [15]. The crystallite size calculated for the ZnO NPs was 45 nm. The UV–visible absorption spectrum of ZnO nanoparticles Fig. 1. The process of preparation of superhydrophobic cotton fabric. Fig. 2. A) XRD 2B) UV–visible spectrum of ZnO nanoparticles and 2C) ATR-FTIR spectra of A) ZnO NPs B) untreated cotton fabric C) HDMS and D) treated superhydrophobic cotton fabric. G.D. Patil et al. / Materials Letters 255 (2019) 126562 3 Fig. 3. SEM images of ZnO NPs incorporated and HDMS coated cotton fabrics. is shown in Fig. 2B which showed the absorption peak at 377 nm. The significant sharp absorption of ZnO indicated formation of the nanoparticles with narrow particle size distribution. The IR spectra of all samples are shown in Fig. 2C. The peaks around 475 to 563 cm 1 are characteristic absorptions peaks of Zn–O bond. The cotton fabric has shown peaks between 900 and 1285 cm 1 corresponding to asymmetric out-of-phase ring stretch: C1–O–C4; b glucosidic bond, 1030 to 1031 cm 1 C-O stretching and 1280 to 1285 cm 1 due to C–H deformation stretch. The spectra of HDMS showed peaks at 1000–1100, 1455, 2850 and 2920 cm 1 corresponding to Si-O-C stretching, C–H bending, and C–H stretching respectively. Instead, the important spectrum of ZnO and HDMS modified showed peaks at 475–563, 1000–1100, 1455, 1712, 2850 and 2920 cm 1, coming from ZnO nanoparticles and HDMS. This confirmed the grafting of HDMS on ZnO and on the fabric [16]. The SEM images of the final superhydrophobic fabric sample taken at different magnifications are illustrated in Fig. 3. The ZnO particles strongly adhered to the cotton yarns coated with the layer of HDMS were seen. The HDMS layer protects the coated ZnO nanoparticles. The resulting contact angle values and durability of the hydrophobicity of fabric sample are due to this modification process. This prevents the detachment of the particles during the washing or use of the fabric. Additionally, due to known antibacterial properties of the ZnO nanoparticles the underlying ZnO particles may impart antibacterial properties to the fabric. The wettability of the cotton fabrics was examined by measuring the water contact angle. The pristine cotton fabrics can be completely wetted due to the abundant hydroxyl groups in its structure. Instead, the ZnO coated and HDMS treated cotton fabrics showed superhydrophobicity. They showed water contact angles of 91° and 152° which confirmed the hydrophobicity of the fabric (Fig. 4). The contact angle remained constant even after 35 washing cycles. 4. Conclusion In conclusion, a new and simple method to prepare superhydrophobic cotton fabrics by post-coating surface modification of ZnO nanoparticles is developed. The padding process helped the penetration and coating of ZnO nanoparticles in the cotton yarns. The post-coating surface modification of the nanoparticles and of the fabric with HDMS resulted in formation of a very thin superhydrophobic layer. The very high water contact angle confirmed the superhydrophobic nature of the fabric. This method can be easily adapted in the textile industrial set-up for the production of superhydrophobic textiles. Declaration of Competing Interest Fig. 4. Water contact angle of cotton fabrics after padding and subsequent modification. 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. 4 G.D. Patil et al. / Materials Letters 255 (2019) 126562 Acknowledgment The financial support by Rashtriya Uchchatar Shiksha Abhiyan (RUSA)’s State Project Directorate (SPD), Mumbai, Maharashtra, India through the center for nanofabrics is gratefully acknowledged. References [1] L. Gao, T.J. McCarthy, Artificial lotus leaf prepared using a patent and a commercial textile, Langmuir 22 (2006) (1945) 5998–6000. [2] W. Chen, A.Y. Fadeev, M.C. Hsieh, D. Öner, J. Youngblood, T.J. McCarthy, Ultrahydrophobic and ultralyophobic surfaces: some comments and examples, Langmuir 15 (1999) 3395–3399. [3] A.Y. Fadeev, T.J. McCarthy, Trialkylsilane monolayers covalently attached to silicon surfaces: wettability studies indicating that molecular topography contributes to contact angle hysteresis, Langmuir 15 (1999) 3759–3766. [4] W. Ming, D. Wu, R. van Benthem, G. de With, Superhydrophobic Films from Raspberry-like Particles, Nano Lett. 5 (2005) 2298–2301. [5] C. 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