SURFACE THERMODYNAMIC PROPERTIES OF MICAS AND RELATED LAYER SILICATE MINERALS

The surface tension values for a series of 2:1 phyllosilicate minerals with different structural characteristics and layer charges ranging f rom 0 to 2 per O-10 group have been examined. The average Lifshitz-van der Waals component (gamma(LW))value is 40.3 +/- 1.9 mJ/m(2), and the average Lewis acid (gamma(+)) parameter is 1.2 +/- 0.6 mJ/m(2) for th ose minerals with a layer charge greater than zero. In contrast, the L ewis base parameter (gamma(-)) varied greatly from a maximum of 59.7 m J/m(2) to a minimum of 23.7 mJ/m(2). Those minerals with a layer charg e of zero (three samples) had smaller gamma(LW) values of 32.0 +/- 1.6 mJ/m(2), slightly larger gamma(+) values of 2.0 +/- 0.4 mJ/m(2) and s ignificantly smaller values of gamma(-) of 4.5 +/- 1.6 mJ/m(2). The hy drophobic versus hydrophilic character of these materials is largely g overned by the value of gamma(-) which is strongly related to the valu e of the layer charge. Thus, the hydrophilicity of a smectite is deter mined by the charge unbalancing ionic substitutions which attract hydr ophilic interlayer cations and render adjacent oxygen atoms of the par ticle surface hydrophilic.