A COMPUTER-MODEL FOR WETTING HYSTERESIS .2. A VIRTUAL WETTABILITY SCANNING BALANCE

We described previously a computer model for wetting hysteresis based on a theoretical analysis of the Wilhelmy wetting experiment. Applying this model to a number of virtual surfaces, we demonstrated that surf ace heterogeneity causes hysteresis in the wetting trace of an otherwi se perfect solid. We now develop a model for the two-meniscus case to emulate liquid membrane wetting. This experiment scans a suspended sol id specimen with a film of liquid contained in a loop attached to a ve rtical drive. After showing how variations in the size and proportion of surface energy domains affect the appearance of virtual wetting tra ces, we estimate the proportion of the surface covered randomly by two materials having different wettabilities, using real immersion and li quid membrane wetting data. The traces produced by the two models matc h the measured traces well. We are also able to mimic the effect of ma croscale heterogeneity superimposed on surfaces featuring wetting hyst eresis caused by microscale heterogeneity, specifically, fibers with n on-uniform applications of finishing agents.