DOUBLE-LAYER INTERACTIONS BETWEEN SILYLATED SILICA SURFACES

Data are presented for the free energy of interaction mediated by water between silica surfaces which have been silylated with (gamma-aminopropyl)dimethylethoxysilane. The measured interactions are of classical DLVO type, with no hydration force evident. Measurements of silylated silica interacting with untreated silica in water indicate an opposite sign of charge between these surfaces and do not exhibit hydration forces. Comparison of the data with theoretical calculations using fully retarded van der Waals interactions and the nonlinear Poisson-Boltzmann equation indicates that the amino-functional surfaces exhibit charge regulation behavior, a model for which is presented.