WETTING CHARACTERISTICS AND STABILITY OF LANGMUIR-BLODGETT CARBOXYLATE MONOLAYERS AT THE SURFACES OF CALCITE AND FLUORITE

Although surface chemistry fundamentals of semisoluble minerals have b een studied by many researchers, detailed understanding of these syste ms is still incomplete. In situ Fourier transform infrared internal re flection spectroscopy (FT-IR/IRS) techniques have recently been used t o successfully describe the adsorption of carboxylates at semisoluble mineral surfaces. The wetting characteristics of these adsorbed films, however, require further consideration. In this regard, the hydrophob icity and stability of transferred Langmuir-Blodgett (LB) monolayers o f fatty acids at fluorite and calcite surfaces have been studied by co ntact angle measurements with water and diiodomethane. Generally, it w as found that the transferred LB monolayers of fatty acids at a calcit e surface are unstable whereas such monolayers transferred onto a fluo rite surface are stable, as revealed from advancing and receding conta ct angle measurements. These results are believed to be due to incompl ete reaction of the fatty acid monolayer at the calcite surface. In ad dition it was found that a closely packed well-ordered stearate monola yer similar to that of a transferred LB monolayer can be formed at flu orite surfaces by spontaneous adsorption and self-assembly from aqueou s solutions.