Contact line structure and dynamics on surfaces with contact angle hysteresis

We examine the wetting properties of surfaces coated by organic monolayers having varying degrees of chemical damage. Macroscopic contact angles and contact angle hysteresis energy serve as one characterization of the surfaces. Measurement of contact line structure to micron resolution over centimeter lengths serves as another characterization. We also examine the dynamics of jumps along the contact line in the different regions around a contact angle hysteresis loop. We investigate the scaling of pinning and elastic energies and the influence of gravity in dictating contact line roughness at various length scales. We measure an approximate power-law for contact line roughness versus length scale. Contrary to many models for weak heterogeneity and dilute pinning, we see no correlation between contact line roughness and contact angle hysteresis. However, the contact line roughness does correlate with the contact angle. These observations reconfirm the dense, strong pinning nature of our surfaces. Qualitative energy functionals provide a useful language for examining and describing the results.