interesting method for determination of dispersion surface
The effect of thermal treatment on the surface properties of silica free energy in this region; however, the results obtained with gel was investigated by the gas phase titration method. The silica this method appeared comparable with other experimental gel samples were heated at 200, 400, and 800ЊC. Ethyl methyl ketone data only for homogeneous surfaces, such as cellulose ( ) was applied as a blocking reagent, and n-octane, benzene, and and carbon adsorbents (13). Ligner et al. (14) investigated chloroform were used as testing probes. A new presentation of the various samples of silica and achieved unrealistic values of results was proposed, which allowed their direct comparison for dispersion surface free energy. different sample areas. It was determined that the thermal treat-Nawrocki (15, 16) proposed a chromatographic method for ment of silica resulted in different changes of testing probe retention
investigation of adsorption sites of extremely high interaction upon adsorption of the same blocking reagent, and this was dependent on the type of surface-molecule interactions (nonspecific, elec-energy, so-called gas phase titration. In this method the subtron-acceptor, and electron-donor, respectively). Certain differstance strongly interacting with the surface (the so-called ences in adsorption sites distribution were found. Then the changes blocking agent) is injected into the column, and then the in free enthalpy of adsorption were calculated for all testing probes. changes in retention volume of the other substance (the testing The results are discussed in terms of condensation of surface silanols agent) are recorded, until the peak of the blocking agent and formation of siloxane bridges. ᭧ 1998 Academic Press appears (15, 16). The adsorption of the blocking agent onto Key Words: silica gel; gas chromatography; gas phase titration; successive sites (i.e., their temporary elimination from the surface heterogeneity.
surface) produces certain changes in the retention of a testing agent. The method was verified in terms of its applicability for investigation of different types of surface-molecule inter-186