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 from 0 to 2 per O10 group have been examined. The average Lifshitz-van der Waals component (ΓLW)value is 40.3 ± 1.9 mJ/m2, and the average Lewis acid (®) parameter is 1.2 ± 0.6 mJ/2 for those minerals with a layer charge greater than zero. In contrast, the Lewis base parameter (γe) varied greatly from a maximum of 59.7 mJ/m to a minimum of 23.7 mJ/m2. Those minerals with a layer charge of zero (three samples) had smaller γLW values of 32.0 ± 1.6 mJ/m2, slightly larger γ® values of 2.0 ± 0.4 mj/m2 and significantly smaller values of γ® of 4.5 ± 1.6 mJ/m2. The hydrophobic versus hydrophilic character of these materials is largely governed by the value of γ° which is strongly related to the value of the layer charge. Thus, the hydrophilicity of a smectite is determined by the charge unbalancing ionic substitutions which attract hydrophilic interlayer cations and render adjacent oxygen atoms of the panicle surface hydrophilic.