Dewetting dynamics on heterogeneous surfaces. A molecular-kinetic treatment

When the molecular-kinetic theory of wetting dynamics on ideal surfaces is applied to heterogeneous solid substrates, effective values of its specific parameters lambda and K-0 are obtained. This paper shows that application of the Blake-Haynes equation to the velocity dependence of dynamic contact angles of water on partially methylated silica yields strong dependencies o f lambda(eff) and K-eff(0) On static wettability and degree of methylation. Such dependencies can be explained by the molecular-kinetic model of dewet ting dynamics on smooth heterogeneous surfaces proposed in this study. Sati sfactory agreement between theory and experimental data is observed below 7 0% methylation, but the values of lambda(eff) and K-eff(0) Obtained at more complete coverage do not follow the theoretical predictions. At this stage we speculate that this disagreement might be due to formation of a rough c oating at higher concentrations of the methylating agent and longer reactio n times. Such an interpretation is based on literature data from ellipsomet ric and AFM studies and elemental analyses of silica surfaces methylated wi th trimethylchlorosilane.