Superhydrophobic fabrics from hybrid silica sol-gel coatings: Structural effect of precursors on wettability and washing
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Jie Ding Human Protection and Performance Division, Defence Science & Technology Organisation (DSTO), Melbourne, VIC 3207 Australia
Yuhua Xue, Xungai Wang, and Tong Lina) Centre for Material and Fibre Innovation, Deakin University, Geelong, VIC 3217 Australia (Received 8 March 2010; accepted 12 April 2010)
Particle-containing silica sol was synthesized by co-hydrolysis and co-condensation of two silane precursors, tetraethylorthosilicate (TEOS) and an organic silane composed of a non-hydrolyzable functional group (e.g., alkyl, fluorinated alkyl, and phenyl), and used to produce superhydrophobic coatings on fabrics. It has been revealed that the nonhydrolyzable functional groups in the organic silanes have a considerable influence on the fabric surface wettability. When the functional group was long chain alkyl (C16), phenyl, or fluorinated alkyl (C8), the treated surfaces were highly superhydrophobic with a water contact angle (CA) greater than 170 , and the CA value was little affected by the fabric type. The washing durability of the superhydrophobic coating was improved by introducing the third silane containing epoxide group, 3-glycidoxypropyltrimethoxysilane (GPTMS), for synthesis. Although the presence of epoxide groups in the coating slightly reduced the fabrics’ superhydrophobicity, the washing durability was considerably improved when polyester and cotton fabrics were used as substrates. I. INTRODUCTION
Superhydrophobicity is typically used to describe surfaces with a water contact angle greater than 150 .1–4 Nature has provided many examples of superhydrophobic surfaces, such as lotus leaves, butterfly wings, and duck feathers, to show water repellent and selfcleaning functions. It is of practical importance to develop superhydrophobic surfaces on fabrics so that they can repel water/ice/snow and have anti-sticking, anti-contaminating, and/or self-cleaning characteristics, but are still permeable to air and moisture for comfort. Extensive research has recently been conducted to understand the formation of superhydrophobicity on various substrates. It has been established that superhydrophobicity depends on not only the surface chemistry but also the surface topology. Two distinct theoretical models (Wenzel and Cassie-Baxter)1,2 have been developed to guide the production of superhydrophobic surfaces by either roughening the surface or lowering the surface free energy, or both. For example, superhydrophobic surfaces were prepared by building a nano-structured surface on a substrate,5–21 followed by treatment with fluoro-containing polymer or silane.9,12 Most of the superhydrophobic techa)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0169
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J. Mater. Res., Vol. 25, No. 7, Jul 2010
niques, however, involve a tedious and multiple-step procedure, which is impractical for large-scale production. In this regard, coating solutions using a one-step preparation and a simple coating process are highly desirable because of the simplicity in both the process
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