Abstract
Physics of wettability and water repellency of fractal-structure surfaces has been reviewed. Wetting behavior of the fractal surface is predicted on the basis of the theory of wettability of a flat and a rough surface. Since the fractal surface has a very large surface-area density, a hydrophobic (hydrophilic) fractal surface can be super water repellent (superwettable). An expression for the contact angle of a liquid droplet placed on a fractal surface is expressed as a function of the fractal dimension, the range of fractal behavior, and the contacting ratio of the surface. Experimental results are also mentioned as to a super-water-repellent fractal surface made of alkylketene dimer; a water droplet on this surface shows a contact angle as large as 174°.
