A study of glass surface heterogeneity and silylation by inverse gas chromatography

The method of obtaining energy and entropy of adsorption on homogeneous:,surfaces from retention time of a chromatographic peak is extended to heterogeneous surfaces. A heterogeneous surface is modeled as a collection of homogeneous patches (sites) and is characterized by a bidimensional distribution of these patches with respect to the energy and entropy of adsorption. This bidimensional distribution can be converted into a one-dimensional distribution of sites with respect to the free energy of adsorption. (The latter can be calculated from chromatographic elution profiles by known methods.) It is shown how to convert the free energy distribution of sites into the distributions of sites with respect to parameters similar to energy and entropy of adsorption. These are regressions of energy and entropy on the free energy of adsorption. Their meaning is elucidated by an-example of the normal bidimensional distribution in {energy, entropy} pairs. The method is applied to the study of the silylation of glass fiber surfaces by trimethoxymethylsilane. The adsorption energy distributions of butanol on the silylated surfaces are obtained for different curing temperatures. At a fixed value of the distribution function in the interval of curing temperature from 180 to 350 degreesC, the adsorption activity of the surface is minimal at-about 290 degreesC.