Electroacoustic detection of the onset of depletion flocculation of latex dispersions by hydroxyethyl cellulose

Depletion flocculation of three poly(methylmethacrylate) (PMMA) latices with particle diameters of 265, 244 and 103 nm by hydroxyethyl cellulose (HEC) with a molecular weight of 1.3 × 106 Da was observed with electroacoustics on a prototype AcoustoSizer-II with a flow-through cell. Triton X-100 was added in order to avoid any bridging flocculation caused by the adsorption of HEC on the surface of the particles. There were significant changes in the magnitude and phase angle of the dynamic mobility spectra accompanying depletion flocculation, which allow a precise estimate to be made of the point of onset of the flocculation in this latex system.