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. W e report rheological measurements of an emulsion of 1-bromohexadecane-in-wa ter flocculated by hydroxy-ethylcellulose. Small-deformation oscillatory me asurements allowed characterization of the structure during formation and a n indication of the strength of the resulting network. Emulsions without po lymer, and polymer solutions alone, showed essentially viscous behavior, wi th dominant viscous modulus over the whole frequency range (0.01-10 Hz). Ho wever, the emulsion containing polymer demonstrated a significant elastic m odulus, dependent on the oil and polymer concentrations, attributable to in terdroplet depletion interactions. Power-law relationships were observed be tween the elastic modulus, elastic strain limit, and oil volume fraction, b ut the indices were lower than those predicted by fractal models, giving un realistic fractal dimensionalities. The modulus increased exponentially wit h polymer concentration, but the elastic strain limit was independent of ad ded polymer. The rate of formation of the network was not consistent with d iffusion-controlled aggregation. (C) 2000 Academic Press.