화학공학소재연구정보센터
Journal of Colloid and Interface Science, Vol.179, No.2, 587-599, 1996
Adsorption of Charged Latex-Particles on Mica Studied by Atomic-Force Microscopy
Atomic force microscopy (AFM) is used to study the localized adsorption of charged latex particles onto a mica substrate with varying adsorption times and solution ionic strengths. Images are obtained by employing tapping mode AFM with silane-treated probes to reduce the intrusive effect of the imaging process on physisorbed particles, The initial kinetics of the adsorption process are found to be diffusion-limited and the long-time asymptotic kinetics are found to resemble those of a random sequential adsorption process. Double-layer screening of interparticle electrostatic repulsions is shown to have a controlling effect on the surface coverage at saturation and, to a lesser degree, on the diffusion-limited rate of adsorption. In situ images of adsorbed layers are compared with those of dried samples to reveal the morphological effects of film evaporation on the microstructure of adsorbed particles. Results show that particles in adsorbed layers of high surface coverage can rearrange into two-dimensional clusters during film evaporation-a phenomenon attributed to capillary forces between particles in near contact. Ordering of particles at the solid-liquid interface is analyzed using two-dimensional radial distribution functions. A high degree of short-range order is found among adsorbed particles when the surface coverage approaches saturation, and a significant reduction in the range of ordering due to double-layer screening of interparticle repulsions is also reflected in the radial distributions.