Influence of surfactants on the disjoining pressure of polymolecular adsorption films of apolar substances at polar substrates

Experimental data obtained by Blake and his co-workers (J. Colloid Interfac e Sci., 1971, vol. 37, no. 4, p. 648) on the wetting and polymolecular adso rption of saturated hydrocarbons on the aluminum surface chemically modifie d with various alcohols are analyzed. The dependences of the disjoining pre ssure of films on their thickness for the unmodified aluminum surface are s hown to significantly deviate from the inverse cubic law predicted by the t heory of dispersion forces. This difference is explained by the effect of t he structural component of disjoining pressure, which is a negative value. Parameters characterizing the dispersion and structural components of disjo ining pressure were estimated using the Frumkin-Derjaguin equation, with al lowances for the influence of alcohol adlayers on the thickness of adsorpti on films and contact angle. It was established that the nature of adsorbate and chemisorbed alcohol molecules affects mainly the structural component. This leads to the variations in thickness of polymolecular films at a cons tant relative pressure of the vapor of the homologous series of both satura ted alcohols and alcohols modifying surface properties of aluminum.