REVERSIBLE AND IRREVERSIBLE ADSORPTION OF PARTICLES ON HOMOGENEOUS SURFACES

The kinetics of localized reversible and irreversible adsorption of interacting particles on homogeneous surfaces was analysed. Asymptotic analytical equations were derived for the surface blocking parameter B(theta), and for adsorption kinetics and adsorption isotherms in the limit of low and high surface concentrations. It was found that the geometrical blocking effect was much more pronounced than the Langmuir model predicts, especially for high surface concentrations and low ionic strengths of suspensions. The new adsorption isotherm formulated indicates that for a large adsorption constant, K(a)BAR, the equilibrium surface concentration becomes proportional to K(a)-1/3BAR, whereas in the Langmuir model this quantity is approached as K(a)-1BAR (for K(a)>>1BAR). In the case of irreversible adsorption the theoretical predictions were experimentally tested by applying the direct microscope observation method. Monodisperse suspensions of negatively charged latex particles were used in these experiments with silanized mica sheets as the adsorbing surface. Our theoretical predictions were quantitatively confirmed, indicating that the Langmuir model is not appropriate for describing localized adsorption of particles on homogeneous surfaces.