Enthalpies of adsorption of non-ionic surfactants from aqueous solutions on to silica

Abstract

Enthalpies of adsorption of three n-alkylpolyethylene glycol non-ionic surfactants (C₁₂E₅, C₁₂E₈ and C₈E₄) on silica immersed in aqueous solutions have been determined by calorimetry. Consecutive stages in the adsorption process are distinguishable by marked changes in the differential enthalpy of adsorption. The results are discussed in terms of the orientation of the surfactant molecules at the silica/water interface as a function of increasing surface coverage. Sudden changes in the enthalpy of adsorption of C₁₂E₅ at saturation monolayer coverage and saturation bilayer coverage of the surface suggested that structural reorganisation akin to phase change was occurring in the interfacial region.