THE EFFECT OF SOLID-SURFACE HETEROGENEITY AND ROUGHNESS ON THE CONTACT-ANGLE DROP (BUBBLE) SIZE RELATIONSHIP

The contact angle for varying sizes of drops and air bubbles was measured on clean, heterogeneous, and rough solid surfaces. A linear correlation of the cosine of the contact angle vs reciprocal of the drop (bubble) base radius was obtained for the tetradecane/water/quartz and air/water/polyethylene systems, in which pure single-component liquids and freshly prepared clean solid surfaces were used. It was found that solid surface imperfections, heterogeneity and/or roughness, affect the contact angle/drop (bubble) size relationship. The change in contact angle with bubble size depended on the extent of solid surface heterogeneity, as was observed for the tetradecane/water/methylated quartz system with varying degrees of quartz methylation. For the air/water/polyethylene and air/water/gold systems, it was found that the slope of a plot of cos theta vs 1/r increased for rough surfaces when compared to that for smooth surfaces, and that these experimental data qualitatively support the modified Wenzel equation which includes the line-tension term. (C) 1994 Academic Press, Inc.