Correlation of viscoelastic properties of concentrated dispersions with their interparticle interaction

Abstract

In this overview the correlation between viscoelastic properties of concentrated dispersions and their interparticle interaction has been demonstrated. Three model polystyrene latex dispersions were studied. The first was an electrostatically stabilised dispersion whereby the viscoelastic properties were measured as a function of volume fraction, φ, at two NaCl concentrations namely 10⁻⁵ and 10⁻³ mol dm⁻³. The viscoelastic properties could be related to double layer repulsion which at a given φ was stronger in 10⁻⁵ compared to 10⁻³ mol dm⁻³ NaCl. The second system was a sterically stabilised dispersion produced either by grafting or physically adsorbing a polymer layer. A predominantly elastic response was produced when the surface-surface separation became less than twice the adsorbed layer thickness, under which condition strong steric respulsion occurs. The third system was flocculated latex dispersions. WEakly flocculated dispersions were obtained by addition of free (non-adsorbing polymer) to a sterically stabilised latex. At a critical free polymer volume fraction, φ ⁺_p , the dispersion showed non-Newtonian flow. It was possible to relate the extrapolated yield stress to the energy of interaction, E _Sep, between the particles. Comparison of E _Sep with theoretical calculation of G _dep (the free energy of interaction due to depletion) showed reasonable agreement. Strongly flocculated dispersions were obtained either by reduction os solvency for a polymer stabilised dispersion or addition of electrolyte to an electrostatically stabilised dispersion. Again good correlation between the viscoelastic properties and the energy of interaction was obtained in this case.