Rheology and particle interaction of thickened latex

Abstract

The pseudoplastic rheological properties of concentrated monodisperse polystyrene latexes with known sodium lauryl sulfate and methylcellulose surface coverages have been studied. It was assumed that the flow units of a concentrated thickened latex subjected to mechanical shear are “flocs” which comprise many particles with immobilized medium in the interstices. During shearing, the particle-particle bonds within the flocs undergo compression and stretching, sometimes breaking and reforming, causing the energy dissipation measured as the yield stress. A model was developed to calculate the average number of bonds per floc and this model was applied to an empirical modification of Firth and Hunter's elastic floc model to correlate the yield stress with the particle-particle separation pressure (defined as a measure of the interaction strength). It was found that the yield stress of a thickened latex is affected by the particle-particle interaction and the morphology of the particle flocs. The particle-particle interaction is affected by the surface coverage of thickener and emulsifier, and their concentrations in the aqueous phase, as well as other factors. The morphology of the particle flocs is affected by the particle interaction and the mechanical treatment. The adsorption of emulsifier and thickener, the rheology of the thickened latexes, the morphology of the particle flocs, and the particle-particle interactions, as well as their interrelationships, are described.