The effect of neutral polymer and nonionic surfactant adsorption on the electroacoustic signals of colloidal silica

The effects of adsorbed neutral polymer and nonionic surfactant on the electroacoustic signals of silica particles have been determined. The dynamic mobility of the particles was measured using an AcoustoSizer (Matec Applied Sciences) during the addition of poly(vinyl alcohol) (PVA) and nonyl phenol ethoxylate (C-9 phi E-N) to the system. Large changes in the dynamic mobility of the coated particles were observed. A theoretical treatment was developed to describe the electroacoustic behavior of an elastic gel layer of uncharged adsorbed polymer and provided a reasonable fit to the experimental dynamic mobility data, This analysis provided information about the thickness and elasticity of the adsorbed layers. The adsorbed layer thickness for PVA compared well with results of other techniques reported in the literature and appeared to be influenced by changes in pH, C-9 phi E-N adsorbed in a relatively dense layer, For both PVA and C-9 phi E-N the thickness of the inner adsorbed layer remained approximately constant, while the outer layer became thicker with increasing concentration and molecular weight. (C) 1997 Academic Press.