Spreading Kinetics of a Drop on a Rough Solid Surface


The effect of surface roughness on spreading rates has been analyzed using a model in which a liquid drop spreads over the surface of a porous medium filled with the same liquid. The equations of motion in the drop are simplified with the lubrication theory approximation and then solved for both zero and small but nonzero contact angles by the method of matched asymptotic expansions. Although the largest pressure gradients and velocity gradients occur near the contact line at the drop periphery, behavior in this region is not singular as found in previous analysis of spreading on perfectly smooth surfaces. The reason no singularities exist is that flow occurs in the "porous medium" underlying the drop, i.e., the region of surface irregularities which is present for all real surfaces. Because the solution is not valid in the initial stages of spreading where experimental data on spreading rates are available, a quantitative comparison of theory and experiment cannot be made at present. The theory does, however, explain all qualitative features observed for spreading drops, e.g., the increase in spreading rate with increasing roughness and the frequent appearance of apparent contact angles significantly different from equilibrium contact angles. © 1983.


Chemical and Biochemical Engineering

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Article - Journal

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© 1983 Elsevier, All rights reserved.

Publication Date

01 Apr 1983