Determination of dispersive properties of silicas by inverse gas chromatography: Variation with surface treatment

The application of inverse gas chromatography (IGC) to the examination of the surface properties of untreated crystalline and fused silica and surface-treated silicas with silane coupling agents is discussed. The carbon content of the silane coupling agents adsorbed on the surface of the silicas was determined by means of a Carbon Determinator. If the assumption is made that each silane coupling agent molecule occupies an area of 0.5 similar to 1 nm(2), the adsorption amounts show that multilayers are generally adsorbed onto the silica surfaces. This paper presents and discusses the dispersive properties expressed by gamma(D)(S), the dispersive component of the surface free energy, as determined at various temperatures. At the same temperature of IGC measurement, the values of gamma(D)(S) determined by IGC were lower for the crystalline silica than for the fused silica. This means that crystalline silica is more stable than fused silica. The silica surface-treated with gamma-methacryloxy propyl trimethoxy silane (MTMS) shows a relatively high gamma(D)(S) value(42.75 mJ.m(-2) at 160 degrees C). This means that this sample should be compatible with polyester(27 +/- 3 mJ.m(-2) at 290 degrees C) at high temperature. The silicas that were surface-treated with gamma-glycidoxy propyl trimethoxy silane (GMS) and gamma-mercapto propyl trimethoxy silane (MCMS) exhibit gamma(D)(S) values that are in close agreement with those of almost all resins(30 mJ.m(-2) at 160 degrees C). The gamma(D)(S) value of the silica surface-treated with gamma-amino propyl triethoxy silane (AES) is similar to that of epoxy resin(40 mJ.m-2 at 80 degrees C). This means that this sample is compatible with epoxy resin at relatively low temperatures.