Surface energy of silica-TEOS-PDMS ormosils

Inverse gas chromatography (IGC) was applied to characterize the surface en ergy of organically modified silicates (ormosils) by measuring the interact ion of molecular organic probes with the ormosil surface. Ormosils were pre pared by the sol-gel method by the reaction of TEOS (tetraethoxysilane), PD MS (polydimethylsiloxane) and different types of silica (Aerosil 130, Aeros il 200 and Aerosil 380). The isosteric heat of adsorption, gamma (D)(s), an d the dispersive component of the surface energy, gamma (D)(s), were estima ted by using the retention volume of different nonpolar and polar probes at infinite dilution. The dispersive component shows an increase as the speci fic surface area of the silica is increased from 29.6 mJ/m(2) to 51.4 mJ/m( 2) at 60 degreesC. Such values are lower than that obtained for aerosil par ticles meaning that PDMS chains impede the interaction with silanol groups located on the silica surface. The specific interaction parameter, I-SP, an d the enthalpy of specific adsorption, DeltaH(a)(SP), of polar probes on th e ormosil surface were also measured in order to obtain the acid-base chara cter of ormosil surface. The DeltaH(a)(SP), was correlated with the donor, DN, and the acceptor, AN, numbers of the probes to quantify the acidic, K-A , and the basic, K-B, parameters of the substrate surface. The obtained res ults suggest that the silica particles were covered by PDMS chains in a dif ferent way depending on the type of silica used. The values of K-A and K-B suggest that the ormosil surface is amphoteric, with predominantly acceptor electron sites.