Computation of Contact Lines on Randomly Heterogeneous Surfaces

Abstract

Liquid wetting on real solid surfaces is significantly more complex than it is on the idealized surfaces of Young's equation. In the case of chemically heterogeneous solid surfaces, simulations of wetting have been carried out only for regularly patterned or one-dimensional surfaces. We describe a computational method for calculating advancing and receding contact lines on two-dimensional solid surfaces with arbitrary patterns of chemical heterogeneity. Results are verified against analytical solutions for homogeneous, single-defect, and striped surfaces. More practical surfaces with randomly placed high energy defects are also modeled. Realistic scatter in the contact angles as well as contact angle hysteresis and stick-slip motion are observed in the simulations. Hysteresis increases with the density of defects, but less so at high densities. The method allows prediction of wetting behavior from surface chemistry for a wide range of heterogeneous surfaces.