Influence of Surface Roughness on Wetting Dynamics

Using the molecular-kinetic theory of wetting, we analyze the dynamic contact angle of a sessile drop of squalane spreading spontaneously on Langmuir-Blodgett multilayer substrates (behenic acid on glass). This allows the effect of microscale roughness on the parameters appearing in the theory to be determined. In particular, it is shown that the jump frequency of liquid molecules at the wetting line decreases with microroughness, supporting the idea that surface defects induce additional pining potentials. The increase in pinning potential can be explained in terms of a linear increase in the activation free energy of wetting with increasing RMS microroughness.