Wetting of silicon wafers by n-alkanes

We examine the wetting behavior of various n-alkanes on both oxide-coated and silane-coated Si wafers. n-Hexane and n-heptane completely wet a silane-coated Si wafer while n-octane exhibits a wetting transition at T-w similar or equal to 60 degreesC. In the complete wetting region, the wetting layer thicknesses as a function of temperature and height are markedly thinner than that which would be predicted by a long-ranged nonretarded dispersion interaction in competition with a gravitationally determined chemical potential. By contrast, the isothermal pressure measurements of Beaglehole and Christenson (J. Phys. Chem. 1992, 96, 3395) for n-pentane on an oxide-coated Si wafer display a much thicker wetting film than would be predicted when the dispersion and pressure-induced chemical potential are taken into account. We resolve these disparate experimental results as a function of temperature, height, and pressure by considering the influence of a number of medium-ranged interactions.