THE WETTING BEHAVIOR OF ALKANES ON WATER

This paper presents recent experimental and theoretical results concer ning the wetting behavior of n-alkanes on water as a function of therm odynamic conditions (i.e., temperature, pressure, etc.). The transitio n from lenses to a macroscopically thick film, that takes place when t he temperature is increased, occurs for n-alkanes on water in a manner very different from that encountered in other fluid systems. For n-pe ntane on water, ellipsometric measurements reveal that the growth of t he pentane layer to a macroscopically thick film occurs in a continuou s manner, for a temperature(approximate to 53 degrees C) corresponding to a change in the sign of the. Hamaker constant. A theoretical appro ach based on the Cahn-Landau theory, which takes into account long-ran ge (van der Waals) forces, enables us to explain the mechanism of this continuous wetting transition. This transition is preceded (at a lowe r temperature) by a discontinuous transition from a thin film (of adso rbed molecules) to a thick (but not macroscopically thick) Nm. The lat ter transition was not visible for pentane on water (it should occur b elow the freezing temperature for water), but we expect to observe it for longer alkanes (e.g., hexane) on water. Work is underway to examin e the wetting behavior of oil/brine systems more representative of res ervoir conditions. (C) 1998 Elsevier Science B.V. All rights reserved.