Creaming and oscillation rheology of weakly flocculated concentrated emulsions

Addition of the non-adsorbing polymer hydroxyethylcellulose (HEC) to oil-in -water emulsions induces flocculation via the depletion mechanism. In the p resent work, we report results on the delay time prior to creaming of hexad ecane-in-water emulsions, flocculated by HEC. In addition, we report on osc illation rheology measurements of a comparable, density-matched system. We compare the two in the search for rheological signatures of delay, and for insight into the delay mechanism. Our results suggest that the commonly use d low-frequency relaxation time does not map simply to delay time. We do, h owever, find that rheology can tell which of our compositions will exhibit delay, and which will not. In addition, those compositions having the great est shear modulus have the longest delay. A simple model, in which the dela y is attributed to a slow creaming stage over a very small distance, produc es an acceptable correlation with the product of complex viscosity and the strain at the end of linearity. Thus the area under the linear portion of t he complex viscosity-strain plot may provide a useful marker of delay time. The unexpected observation of a liquid-like regime at high oscillation fre quency merits further investigation. (C) 2001 Elsevier Science B.V. All rig hts reserved.