THE ADSORPTION OF NONIONIC SURFACTANTS IN HYDROPHILIC CYLINDRICAL PORES .2. MEAN-FIELD LATTICE CALCULATIONS

The adsorption behavior of nonionic surfactants in hydrophilic cylindr ical pores has been studied with a mean field lattice (MFL) theory. Th e pore radius has two important influences on the adsorption isotherm. With decreasing radius (i) the adsorbed amount decreases and (ii) the step in the isotherm shifts to lower concentration. This behavior is rather generic. Neither the molecular architecture nor the adsorption energy influences these qualitative features. However, the position of the step in the isotherm becomes more sensitive to the curvature as t he adsorption energy increases, just as has been predicted with the se mithermodynamic (ST) theory. We have been partly successful in predict ing the curvature behavior from the excess grand potential density pro file of the flat adsorbed layer. All trends found with the full MFL ca lculations could be reproduced with the help of the curvature constant s, calculated fr om the profile of the flat layer. However. the curvat ure constant was underestimated. At the step in the isotherm the error was about 25%.