RHEOLOGY OF OIL-IN-WATER EMULSIONS

The effect of interfacial tension on the steady-flow and dynamic visco elastic behavior of emulsions are studied experimentally. At very low interfacial tensions and low volume fractions, the viscosity decreases with increasing shear rate and becomes constant at high shear rates. The high-shear-rate Newtonian viscosity is not affected by interfacial tension, but the transition from pseudoplastic to Newtonian flow shif ts to lower shear rates as the interfacial tension decreases. At an in terfacial tension of 5 x 10(-3) Nm-1, the viscosity decreases, passes through a minimum, and then increases as the shear rate is increased. The dilatant behavior may be attributed to elastic responses of interf aces during collision of drops. At high volume fractions, the emulsion s show remarkable elasticity resulting from the interfacial energy ass ociated with deformation of liquid films. The modulus and viscosity ar e proportional to interfacial tension and inversely proportional to dr op size.