Design of a Superhydrophobic Surface Using Woven Structures

Abstract

The relationship between surface tension and roughness is reviewed. The Cassie-Baxter model is restated in its original form, which better describes the most general cases of surface roughness. Using mechanical and chemical surface modification of nylon 6,6 woven fabric, an artificial superhydrophobic surface was prepared. A plain woven fabric mimicking the Lotus leaf was created by further grafting 1H,1H-perfluorooctylamine or octadecylamine to poly(acrylic acid) chains which had previously been grafted onto a nylon 6,6 woven fabric surface. Water contact angles as high as 168 degrees were achieved. Good agreement between the predictions based on the original Cassie-Baxter model and experiments was obtained. The version of the Cassie-Baxter model in current use could not be applied to this problem since the surface area fractions in this form is valid only when the liquid is in contact with a flat, porous surface. The angle at which a water droplet rolls off the surface has also been used to define a superhydrophobic surface. It is shown that the roll-off angle is highly dependent on droplet size. The roll-off angles of these superhydrophobic surfaces were less than 5 degrees when a 0.5 mL water droplet was applied.

Fabrics with Tunable Oleophobicity

“…[37][38][39][40] Fig. 3c shows an electron micrograph of a commercial polyester fabric (Anticon 100 clean-room wipe).…”

Superhydrophobic cotton fabrics prepared by sol–gel coating of TiO2and surface hydrophobization

“…Equation (1) has recently been modified to account for the local surface roughness on the wetted area as follows [14,16,30]:…”

“…We suppose that the obtained advancing and receding contact angles are not the true accurate values owing to the effect of the protruding fibers. Because the protruding fibers exhibit elasticity and also forces on the water droplet [11], it is difficult to yield accurate values for the advancing and receding water contact angles [14,16]. Therefore, only static CAs are reported here, as shown in table 1.…”

“…Among others, superhydrophobic textiles have been successfully obtained by a number of different approaches [9][10][11][12][13][14][15][16]. For example, Gao and McCarthy, according to a 1945 patent, grafted a silicone coating to a microfiber polyester fabric to render the fabric superhydrophobic [9], but the microfiber polyester fabric (with a single fiber as small as 2-5 µm) must be tightly woven, and this approach may not be suited to cotton textiles.…”

“…For oleophobic textiles, perfluoralkyl silane was used for surface modification. Michielsen and Lee [16] used mechanical and chemical surface modifications with further grafting of 1H,1H-perfluorooctylamine or octadecylamine to poly(acrylic acid) chains, which was previously grafted onto a nylon 6,6 woven fabric surface, to prepare artificial superhydrophobic surfaces. Li et al [15] prepared superhydrophobic surfaces from water glass and nonfluorinated alkylsilane on cotton substrates.…”