The effects of surface energy and roughness on the hydrophobicity of woven fabrics

Abstract

The wetting behavior of a hydrophobic rough surface is investigated on a surface fabricated by applying low surface tension materials such as silicone or fluoropolymer to polyester woven fabric consisting of multifilament yarns. The roughness factor of various woven fabrics can be calculated by Wenzel's and Cassie-Baxter's equations. For the fabrics treated with silicone or fluoropolymer, the Cassie-Baxter model was applied, showing a level of agreement for the fabric specimens non-textured filament fibers between the predicted contact angles and the measured values. More precisely, the fabrics treated with silicone or fluoropolymer represent the transitional state between the Wenzel type and the Cassie-Baxter type; that is, the fractional contact area between the water and air f 2 is greater than zero, and the sum of the fractional contact areas for solid-water f 1 and air-water f 2 is greater than 1. A surface with lower energy and higher roughness gave f 1 + f 2 close to 1 with smaller f 1 and larger f 2 , which resulted in a high contact angle. KeywordsHydrophobic, lotus effect, roughness factor, Wenzel model, Cassie-Baxter model Inspired by natural surfaces like the lotus leaf, surfaces with extreme water repellent properties have received considerable interest in the last decade. 1 The studies by Wenzel 2 and Cassie and Baxter 3 showed that the rough and porous structure of a surface combined with a low surface energy can contribute to the hydrophobicity of a surface. The surface of the lotus leaf is chemically made of wax and structurally has two levels of roughness consisting of nano-scale bumps on the surface of micro-scale protrusions that enables the trapping of air underneath water droplets, thereby contributing to a well-designed superhydrophobic surface. 4 Drops of water deposited on such superhydrophobic surfaces exhibit extremely high contact angles (>150 ) and roll off at slight inclinations. Potential applications range from non-wettable, quick-drying surfaces to anti-fouling or self-cleaning surfaces. 4-8 In view of the significant potential of such surfaces for numerous scientific and industrial applications, many strategies to create superhydrophobic surfaces have been published to date. [6][7][8][9] As a measure of the hydrophobicity of the fabric surface, the static contact angle is often used; a larger contact angle with a smaller contact angle hysteresis represents higher hydrophobicity. Wenzel 2 and Cassie and Baxter 3 suggested the theoretical models for contact angles of a liquid on a surface with certain geometry. 9 Different contact angles may result with the same roughness texture depending on how the liquid is configured on the surface. When a liquid completely fills all the spaces in the pores, the Wenzel model is applied to describe the contact angle W r as a function of the ratio of the liquid-solid contact area to the

Interaction of Surface Energy Components between Solid and Liquid on Wettability, and Its Application to Textile Anti-Wetting Finish

“…Early studies on anti-wetting surface modification have been focused on novel anti-wetting chemicals with a low surface energy or durable treatment methods [5,30,31,32]. Fluorinated compounds have been extensively applied in anti-wetting finish methods due to their very low surface energy [19,20,31,33,34]. Recently the environmental concern has been raised on the use of perfluorinated compounds having chain lengths of eight carbons (C8) or longer [35], and the alternatives to C8 perfluorinated chemicals, including silane with long carbon chains, are being explored [36,37,38].…”

“…Thus, the implementation of surface roughness becomes significant in achieving the high level of anti-wetting property [43,44]. When an anti-wetting coating is applied to fabrics, the surface usually displays a higher level of anti-wetting than flat film surfaces, due to the presence of roughness formed by the microscale fibers and yarns [19,20,32,33,45]. With the additional roughness formed by the particle deposition [38,45] or the surface etching [36,46,47], the fabric surface can further enhance the anti-wetting property [9,22,25,26].…”

Development of a superhydrophobic electrospun poly(vinylidene fluoride) webviaplasma etching and water immersion for energy harvesting applications

“…Superhydrophobic surfaces have been fabricated by dip-coating, spray-coating, sol-gel methods, layer by layer assembly, chemical vapor deposition, etc. [38][39][40][41][42] However, all these techniques include complicated procedures and additional coating processes with low surface energy materials.…”

Electric heated cotton fabrics with durable conductivity and self-cleaning properties

“…19 To achieve this selfcleaning property, both high contact angle and low contact angle hysteresis are required. [16][17][18]41,[48][49][50] To evaluate the self-cleaning properties of the fabricated superhydrophobic surface, water droplets were dropped on the sample aer sprinkling silicon carbide particles on the surface to observe the removal of particles by the water droplets. Fig.…”