INVESTIGATION OF THE SURFACE FREE-ENERGY COMPONENTS OF THERMALLY TREATED CONTROLLED POROSITY GLASSES BY INVERSE GAS-CHROMATOGRAPHY

Adsorption isotherms of n-octane and toluene were measured on thermally treated controlled porosity glasses (CPG) and on boron-coated silica gel (SG). From the isotherms the film pressure (pi) for both adsorbates was determined. Based on extrapolated pi(max) values the dispersion (gamma-S(d) and the non-dispersion (gamma-S(n) components of the surface free energy for all the investigated materials were calculated. It was found that the changes in gamma-S(d) caused by the surface modification were relatively small (approximately 4 mJ/m2), while those of gamma-S(n) were significant. The boron compounds decrease the gamma-S(n) value from 145-160 to 37-55 mJ/m2. The dependences between DELTA-pi/DELTA-alpha and the adsorbed amount can give some about the adsorption mechanism and surface homogeneity. The presence of Na on the surface of both CPG and SG seems to be a more important factor for adsorption than that of boron. The significant changes in non-dispersion interactions were attributed to surface dehydroxylation, which may result from both the thermal treatment and the presence of boron on the surface.