THERMOTROPIC PHASE-TRANSITION OF ADSORBED OLEATE SPECIES AT A FLUORITE SURFACE BY INSITU FT-IR/IRS SPECTROSCOPY

In situ FT-IR/IRS analysis of the fluorite/oleate system at pH 9.5 has provided spectral data which indicate that thermotropic phase transitions of chemisorbed calcium oleate occur at the fluorite surface. Specifically, at room temperature the chemisorbed oleate at submonolayer coverage transforms to the more rigidtrans state.In situ surface measurements further show that with an increase in temperature the chemisorbed calcium oleate, in thetrans state at 25°C, transforms, "melts," to agauche state with a transition temperature between 25 and 40°C corresponding to the coagel to micelle transition temperature for the bulk sodium oleate/water system as determined from transmission FT-IR experiments by previous investigators. © 1991 Academic Press, Inc. All rights reserved.