A COMPUTER-MODEL FOR WETTING HYSTERESIS .3. WETTING BEHAVIOR OF SPATIALLY ENCODED HETEROGENEOUS SURFACES

Heterogeneous surfaces are often modeled as a distribution of homogene ous ''patches'' of different energies. Direct testing of these models has not been possible, since the heterogeneous surfaces that have been studied are, at the start, ill-defined. We have synthesized tailored heterogeneous surfaces using a new combinatorial technique, designated PROLAPS. This method creates a mosaic of spatially encoded immobilize d materials, i.e. each immobilized material is identified by its posit ion on the support. The wetting behavior of glass cover slips on which compounds of different wettability have been synthesized in well-defi ned patterns is described. A model for wetting hysteresis was found to accurately mimic fluctuations in meniscus height as the wetting liqui d encounters zones of alternating high and low solid surface energy. T he changes in contact angle as the meniscus encounters transitions fro m regions of low to high surface energy and vice versa are not as abru pt in real life as in model data.