The effects of adsorbed neutral polymer and nonionic surfactant ies of neutral polymer adsorption, research has been directed on the electroacoustic signals of silica particles have been detertoward the development of new experimental techniques in mined. The dynamic mobility of the particles was measured using order to obtain more information about the adsorbed layer. an AcoustoSizer (Matec Applied Sciences) during the addition of These techniques include small angle neutron scattering poly(vinyl alcohol) (PVA) and nonyl phenol ethoxylate (C 9 fE N ) (SANS) (24, 25), NMR (24, 26), and surface forces (27). to the system. Large changes in the dynamic mobility of the coated Photon correlation spectroscopy (PCS) has also been used particles were observed. A theoretical treatment was developed (28-32) to study the thickness and structure of adsorbed to describe the electroacoustic behavior of an elastic gel layer of layers of polymer. uncharged adsorbed polymer and provided a reasonable fit to the experimental dynamic mobility data. This analysis provided infor-Most studies of nonionic surfactant adsorption involve mation about the thickness and elasticity of the adsorbed layers. either alkyl polyoxyethylene, C x E y , or alkyl phenol polyoxy-The adsorbed layer thickness for PVA compared well with results ethylene, C x fE y , molecules, as these are commonly used in of other techniques reported in the literature and appeared to be commercial applications. A review by Clunie and Ingram influenced by changes in pH. C 9 fE N adsorbed in a relatively dense (33) has highlighted some general characteristics of nonlayer. For both PVA and C 9 fE N , the thickness of the inner adionic surfactant adsorption. The adsorption isotherms are sorbed layer remained approximately constant, while the outer usually of the Langmuir type, with surfactant displacing walayer became thicker with increasing concentration and molecular ter from the surface at low concentrations and forming a flat weight. α§ 1997 Academic Press monolayer near the cmc. If the concentration of surfactant