Elsevier

Applied Surface Science

Volume 258, Issue 11, 15 March 2012, Pages 4888-4892
Applied Surface Science

Thermoresponsive PNIPAAm-modified cotton fabric surfaces that switch between superhydrophilicity and superhydrophobicity

https://doi.org/10.1016/j.apsusc.2012.01.107Get rights and content

Abstract

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto the cotton fabric by atom transfer radical polymerization (ATRP). Introducing 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTS) onto the surface, the density of PNIPAAm chains can be adjusted because of the competitive reactions of (3-aminopropyl) triethoxysilane (APS) and PFDTS. With the appropriate ratio of APS and PFDTS, the cotton fabric can be switched from superhydrophilic to superhydrophobic by controlling temperature. The prepared cotton fabric may find application in functional textiles, soft and folding superhydrophobic materials.

Highlights

► PNIPAAm was grafted onto cotton fabric by ATRP. ► The density of PNIPAAm chains can be adjusted by introducing PFDTS to the surface. ► The as-prepared surface had controllable wettability by changing temperature. ► The prepared cotton fabric may find application in functional textiles.

Introduction

In recent years, smart responsive surfaces with controllable wettability which can be prepared by modification of stimuli-responsive materials on solid substrates, has received great attention due to the excellent response of their physical and chemical properties to external stimuli, such as temperature [1], [2], light illumination [3], [4], [5], pH value [6], electric field [7], and solvent and solute [8]. PNIPAAm, with a lower critical solution temperature (LCST) about 32 °C, is a well-studied thermoresponsive and biocompatible polymer which has wide use in many applications, e.g. attachment–detachment controllable surface for proteins [9], blood-compatible materials [10], temperature controllable water permeation device [11] and so on [12]. When PNIPAAm and its copolymers are grafted onto certain solid substrates, it can be used as smart responsive materials. Several papers have reported that the PNIPAAm can be grafted onto solid substrate by ATRP. Jiang and co-workers modified PNIPAAm on rough silicon substrate, and the as-prepared surface can be transformed from superhydrophilic to superhydrophobic by adjusting the temperature when the groove spacing of the substrate was small enough [1]. They also obtained a dual-stimuli-responsive surface with reversible switching between superhydrophilic and superhydrophobic, and responsibility to both temperature and pH, by grafting a poly(N-isopropyl acrylamide-co-acrylic acid) copolymer on a roughly etched silicon substrate [13]. Lindqvist et al. reported the grafting PNIPAAm from filter paper which could alter the wettability from 0° to 110° at temperatures below and above LCST [14].

In this study, cotton fabric was first chosen as the substrate to graft from PNIPAAm, because of its biodegradation, softness and high roughness on the surface. The low surface energy regent, PFDTS was introduced into the surface to adjust the density of the PNIPAAm chains and reduce the surface energy of the cotton fabric. In the previous reports, Sun et al. used heptadecafluorodecyltrimethoxysilane and (3-aminopropyl)-trimethoxysilane to modify on silicon wafer, and then grafted PNIPAAm from this substrate by ATRP, resulting in the wettability only switching ranging between 75.9° and 113.0° which limited the application of the biointerface materials [15]. Liu and co-workers used the mixture of silane 3-(trichlorosilyl)propyl-2-bromo-2-methylpropanoate and 1H,1H,2H,2H-perfluoro-octyltrichlorosilane to modify anodized alumina substrates, then modified the substrate with PNIPAAm by ATRP, and obtained a surface with switching water drop adhesion by controlling the temperature [16]. Different from the above reported literatures, we used PFDTS and APS to modify the cotton fabric and can obtain a PNIPAAm grafting cotton fabric surface with controllable wettability by changing the temperature. What is more, the cotton fabric was a soft and folding substrate which can broaden the application of superhydrophobic materials.

Section snippets

Materials

Cotton fabrics were purchased from a local fabric store. Before use, the cotton fabrics were immersed in a 0.2 M of NaOH aqueous solution for 30 min, cleaned by ultrasonic washing in acetone and water respectively, and dried at 120 °C. N-isopropylacrylamide monomer (NIPAAm, Aladdin, 98%) was recrystallized from hexane for two times. CuBr (Sinopharm Chemical Reagent Factory, 98.5%) was washed with acetic acid several times and then washed with ethanol until the pH reached 7. PFDTS (Aldrich, 97%),

Results and discussion

PNIPAAm is a temperature responsive polymer which can change its molecular conformation. When the temperature is lower than the LCST, the PNIPAAm exhibits an extended hydrophilic chain conformation. The PNIPAAm polymer chain behaves like a hydrophobic aggregate above its LCST. Cotton fabric was used as the substrate, because there were a large number of hydroxyl groups and the surface of cotton fabric was rough. In this work, ATRP was used to graft PNIPAAm onto the cotton fabric.

When the cotton

Conclusion

In conclusion, PNIPAAm brushes were successfully grafted onto the cotton fabrics by ATRP. By introducing PFDTS molecules onto the surface, the density of the PNIPAAm chains can be controlled. When the ratio of APS/PFDTS was in a proper ratio, the prepared cotton fabric surface can transform from superhydrophilic to superhydrophobic by adjusting the temperature. What is more, this wettability switching was reversible. This temperature responsive cotton fabric may have potential applications in

Acknowledgments

The financial supports from the National Science Foundation for Distinguished Young Scholars of China (grant no. 51025517) and the National Defense Basic Scientific Research Project (A1320110011) are duly acknowledged.

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