Effects of surface roughness on advancing and receding contact angles

Abstract

The ability of liquid drops to advance and recede over a solid surface of varying surface energy and roughness, including drugs compacted into disks, has been investigated by measuring advancing and receding contact angles. For the relatively non-polar solids used in this study, roughness of the type encountered in pharmaceutical systems produces significant contact angle hysteresis by primarily affecting the receding angle. Despite the apparent random nature of the surface roughness of compacted disks, it is concluded that the concentric groove model by Shuttleworth and Bailey (Disc. Faraday Soc., 3 (1948) 16) best describes the effect of roughness qualitatively. In view of the relatively small effect of such roughness on advancing contact angles, it is concluded that such angles measured on highly compressed disks generally can be taken to be reasonable estimates of the intrinsic equilibrium contact angle.