TENSIOMETRIC STUDIES ON WETTING OF SOLID SURFACES

Theoretical studies on the wetting of cylindrical solid surfaces with axisymmetric rugosities explicitly showed the presence of contact angle hysteresis, non-equilibrium jumps during contact line motion and the formation of composite surfaces. For physically rough surfaces with unidirectional randomness it was shown that hysteresis increases with decreasing roughness dimensions and with increasing standard deviation in the solid surface slope distribution.;High energy surfaces such as platinum and quartz exhibit a regular stick-jump behavior when wetted with water above a very low critical contact line velocity. This is caused by minute amounts of surface active impurities in the system. From the experimental data it can be deduced that surface active molecules diffuse onto and over the solid surface.;A relaxation of the contact angle was observed when an initially slow moving contact line was brought to a full stop. This is attributed to the slow establishment of a new equilibrium, possibly by surface capillary waves, involving metastable contact line positions separated by energy barriers. For receding contact angles, the main cause of the relaxation seems to be a stabilization of a liquid film left behind a receding contact line.;The observations made in this study contribute to a better understanding of the complicated nature of the wetting of solids.;The wetting of solid surfaces by liquids was investigated by a new tensiometric technique called capillarography. At large roughness wavelengths ((TURN)100 (mu)m) the contribution of concentric sawtooth-shaped regular roughness was found to be close to the values calculated theoretically. At smaller roughness wavelengths ((TURN)1 (mu)m) the wetting is complicated by intrinsic roughness and chemical heterogeneity.