A thermodynamic approach to the effect of pressure on solid/liquid interfacial tensions

In this work the effect of pressure on solid/liquid interfacial tension is analysed by use of the surface thermodynamics of Gibbs. For solid/one-compo nent-liquid interfaces the effect of pressure is dependent on the excess of liquid molecules at the interface. The surface excesses and the effect of pressure for the calcite/water and calcite/n-decane interfaces are discusse d by use of vapour adsorption data, and two molecular layers are found to r epresent the majority of the surface pressures. Based on +/- 25% surface ex cess of the two first molecular layers, and a pressure increase from 5 to 4 0 MPa at 25 degrees C, the changes of the surface pressures due to pressure are calculated to be about +/- 33% and +/- 2% at the calcite/n-decane and calcite/water interface, respectively. The higher relative pressure effect for the calciteln-decane interface is due to the lower total surface pressu re of n-decane than that for the water, 22.7 and 270 mN m(-1), respectively . The absolute changes of the surface pressures are +/-7.4 and +/-5 mN m(-1 ) for n-decane and water, respectively. The major uncertainty in these calc ulations is related to the magnitudes of the surface excesses. (C) 1999 Els evier Science B.V. All rights reserved.