Abstract
In this paper, the inverse gas chromatography (IGC) technique was used to calculate the acid–base superficial characteristics of some solid substrates such as oxides, polymer and polymer adsorbed on oxide. The acid–base constants were calculated for many solids: Monogal, MgO, ZnO, SiO 2 and Al 2O 3, four different carbon fibres and polymers such as poly(methyl methacrylate) (PMMA) at various tacticities adsorbed on alumina or silica. The determination, by IGC, of the specific free enthalpy Δ G sp a of adsorption corresponding to the specific interactions of polar molecules with the solid, as a function of the temperature, allowed to obtain the specific enthalpy Δ H sp a and specific entropy Δ S sp a. Knowing Δ H sp a of the various polar molecules, we were able to determine the acidic constant K A and basic constant K D, the two constants characterizing solid substrates like PMMA, PMMA–SiO 2 or PMMA–Al 2O 3, using the following classical expression: − ΔH sp a =K A DN+K D AN where DN and AN are respectively the electron donor and acceptor numbers of the solid substrates. This study showed an important effect of the tacticity on the acid–base properties. On the other hand, we proved that the previous relation was not correct in many cases and especially for some oxides (as MgO, ZnO and Monogal) and carbon fibres. We proposed a new relationship by adding a third parameter K reflecting the amphoteric character of the solid according to: − ΔH sp a =K A DN+K D AN−KDN×AN.
Published Version
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