Repelling liquid using squishy surfaces

Abstract

The ability to create surfaces with extreme repellency for both high and low surface tension liquids has broad technological implications in areas ranging from fuel transport, drag reduction to anti-icing, anti-fouling applications. Here, I will look into the ability of four classes of squishy surfaces to repel an impinging liquid droplet or jet: 1) surfaces grafted with 'liquid-like’ polymer brushes , 2) lotus-effect surfaces, 3) lubricated surfaces, and 4) soft gels. In each case, there is an element of 'squishiness’ in the material that leads to unusual wetting properties. In a lubricated surface, this comes in the form of a mobile interface (liquid droplet-lubricant oil) that can deform in response to capillary forces, resulting in the absence of any contact-line pinning. A soft gel, which contains up to 90 wt% liquid, is inherently squishy; as a result, a liquid jet can stably bounce off a sufficiently soft gel, by following the contour of the dimple created due to pressure upon impact, irrespective of the wetting properties of the liquid. I will describe in details the mechanisms of these liquid-repellencies and show how the squishiness of such surfaces results in qualitatively different behavior from their hard, rigid counterparts. While the focus of this dissertation is on repelling liquid, many of the experimental approaches and analysis described here can be more broadly applied to other subjects, ranging from ice-repellency to self-assembly of colloids into a photonic crystal.