The influence of polymer impregnation ratios on the surface properties of fumed silicas as determined by inverse gas chromatography

The evolution of the surface properties of two types of fumed silica impregnated with different amounts of different polymers (polyethyleneglycol (PEG), polyvinylchloride (PVC), polyvinylmethylketon (PVMK) or polystyren (PS)) has been studied by inverse gas chromatography at infinite dilution. IGC-ID is a convenient method for the examination of the surface properties of a solid in which molecular probes are injected in very small amounts so that they mainly interact with sites of highest energy. The impregnation of silica with increasing polymer ratios leads to the progressive killing of these sites, allowing the probes to access the less energetic free sites. The polymers were chosen on the basis of their acidic or basic properties. A basic polymer, like PEG or PS, should first interact with the silanol groups, whereas an acidic polymer should interact preferentially with siloxane bridges. What behaviour will be adopted by an amphoteric polymer, such as PVMK? also allows a fine estimate of the number of monomer units per nanometer square necessary to form a polymer monolayer at the surface of the solid. Finally, we have followed the evolution of the glassy transition temperature of the adsorbed polymer, with the PVC impregnation ratios on a silica. Correlatively, the enthalpies of adsorption below and above this critical temperature were determined. Hence, we will demonstrate that it will be possible to examine the evolution of the surface properties from the point of view of the polymer layer adsorbed on the silica surface.