Spreading of liquids on rough surfaces

Spreading of liquids on rough surfaces was studied experimentally and theoretically. Seven liquids, with viscosities spanning over a few orders of magnitude, were used on glass surfaces of five different values of average roughness, ranging from about 0.07 to about 40 mu m. It is shown that the experimental data can be empirically correlated by a power law. In addition, a simple theoretical model is presented, which takes into account the capillary flow of liquid into the roughness grooves. A Lucas-Washburn type of analysis for this flow is modified by taking into account the variation in the length of the capillary itself, due to the variation in the location of the edge of the drop that feeds the capillary flow. Results of the theoretical calculations are shown to be in good agreement with the experimental data. (C) 1999 Elsevier Science B.V. All rights reserved.