Surface methylation of aerosil and its influence on the adsorption of water

Reversible adsorption isotherms at different temperatures have been used to study the system of water adsorbed on Aerosil and on Aerosil whose surface has been partially methylated with trimethylchlorosilane. The change in the shape of the isotherm upon surface methylation from type II to type III, according to Brunauer's classification, renders difficult the calculation of the capacity of the monolayer; however, in this case it can be obtained by Kaganer's method. The variation in the mobility of the monolayer on surface methylation can be shown by comparing the experimental and theoretical integral entropies, while the molecules adsorbed in the multilayer region always have a high degree of freedom.