RHEOLOGICAL PROPERTIES OF CONCENTRATED STERICALLY STABILIZED LATEX DISPERSIONS IN THE PRESENCE OF HYDROXYETHYL CELLULOSE

The effect of addition of hydroxyethyl cellulose (HEC) with three different molecular weights (70,000, 124,000, and 223,000) on the viscoelastic properties of polystyrene latex dispersions was investigated using steady state and oscillatory techniques. The latex contained grafted poly(ethylene oxide) (PEO) and three different particle diameters (D = 147, 435, and 915 nm) were used. Results were obtained as a function of HEC volume fraction, φp, and particle volume fraction, φs. A scaling law was used to describe the dependence of the extrapolated yield value, τβ, with φs above the critical flocculation polymer volume fraction, φ+p. The exponent in φs was constant and of the order of 2.8, which is close to that for a diffusion controlled aggregation process. τβ was used to calculate the energy of separation between the particles in a flocculated structure. The free energy of attraction due to depletion, Gdep was calculated using three theories. The storage modulus, G′, was measured as a function of φp, φs, particle size (D), and molecular weight of HEC. The results showed an increase in G′ with increase in φp as expected. However, G′ increased with increase in D which is opposite to the effect found previously using PEO. In addition, the molecular weight of HEC did not significantly affect the dependence of G′ on φs. These results were unexpected; tentative explanations for them are given. © 1993 by Academic Press, Inc.