Acid–Base interactions in filler characterization by inverse gas chromatography



Glass beads as model fillers were characterized by inverse gas chromatography (IGC) according to the Lewis acid–Lewis base (donor–acceptor) concepts as adapted by Fowkes. A range of organic probes (acidic chloromethanes, neutral n-alkanes, and basic acetone and diethylether) was used to elucidate the acid–base nature of the glass bead surface. The untreated glass bead surface was found to contain predominantly acidic sites while the treated glass bead (treated with an aminopropyltriethoxysilane coupling agent) was more basic than its unmodified counterpart. Calculation of the enthalpies of acid–base interactions (ΔHab) form the retention behavior of the basic probes with the two glass beads produced at least an 8-kJ/mol difference between the two glass types, the ΔHab of the untreated glass being greater than the treated glass. A difference of this magnitude is sufficient to produce a corresponding difference in the interfacial behavior of the two glass types. Therefore, IGC can be used as a quantitative technique for characterizing filler surfaces.