Characterization of a polydisperse depletion-flocculated emulsion: III. Oscillatory rheological measurements

The addition of nonadsorbing polymer to an alkane-in-water emulsion causes the droplets to flocculate into a space-spanning, stress-bearing network. We report rheological measurements of an emulsion of 1-bromohexadecane-in-water flocculated by hydroxy-ethylcellulose. Small-deformation oscillatory measurements allowed characterization of the structure during formation and an indication of the strength of the resulting network. Emulsions without polymer, and polymer solutions alone, showed essentially viscous behavior, with dominant viscous modulus over the whole frequency range (0.01-10 Hz). However, the emulsion containing polymer demonstrated a significant elastic modulus, dependent on the oil and polymer concentrations, attributable to interdroplet depletion interactions. Power-law relationships were observed between the elastic modulus, elastic strain limit, and oil volume fraction, but the indices were lower than those predicted by fractal models, giving unrealistic fractal dimensionalities. The modulus increased exponentially with polymer concentration, but the elastic strain limit was independent of added polymer. The rate of formation of the network was not consistent with diffusion-controlled aggregation. Copyright 2000 Academic Press.