Microcomputer-enhanced optical investigation of transport processes with phase change in near-equilibrium thin liquid films

Abstract

The near-equilibrium thickness profiles of an extended meniscus in the contact line region of a completely wetting film of octane on an inclined, flat plate were measured using an ellipsometer and a microcomputer-enhanced interferometer. The extreme sensitivity of the system to the nonequilibrium effects associated with volatile liquids is demonstrated and evaluated. The inferred equilibrium profile agreed with theoretical predictions of the width of the transition region, the curvature, and the thickness of the adsorbed film. The procedures allow the interfacial properties of the system to be evaluated in situ at the start of dynamic studies and then to be used to describe the transport processes associated with evaporation and condensation. The effect of transport processes on the thickness profile agreed with previous theoretical models. The convenience of microcomputer-enhanced video microscopy naturally leads to a better understanding of the transport processes in the contact line region. The results demonstrate that the near-equilibrium processes of change-of-phase heat transfer and fluid flow in thin films are intrinsically connected because of their common dependence on the intermolecular force field and gravity.