The Apparent Contact Angle of Liquids on Finely-Grooved Solid Surfaces-A SEM Study

Abstract

Abstract A finely parallel-grooved nitrocellulose surface has been employed as a model to study by scanning electron microscopy the influence of roughness on the spreading equilibrium of liquid drops. The Cassie and Baxter equation for spherical drops on a composite interface was experimentally confirmed with mercury and a similar equation derived for a cylindrical drop has also been shown to be approximately valid for liquid polyphenylether. The observed drop shapes have been explained and the importance of groove edges demonstrated. Direct measurements of the microscopic contact angle of mercury locally on the grooved surfaces were found to be approximately the same for the smooth ungrooved surface.