Yield stress and viscoelastic properties of high internal phase ratio emulsions

 The rheology of high internal phase ratio oil-in-water emulsions was investigated using a controlled-stress rheometer. The dispersed-phase (oil) concentration was varied from 71.24 to 89.61% by volume. Three different types of rheological experiments were conducted for each emulsion, namely: steady shear, oscillatory shear, and creep/recovery experiments. All the emulsions investigated in this study possess a yield stress. The yield-stress values obtained from different rheological experiments for the same emulsion show good agreement with each other. The yield-stress value increases exponentially with an increase in the dispersed-phase concentration. The yield-stress data of this study can be described quite well with the Princen and Kiss equation for high internal phase ratio emulsions provided that the thickness of the interdroplet films is taken into account. For any given emulsion, the storage modulus, measured in the linear viscoelastic region, is found to be constant, independent of the frequency, indicating a solid-like behaviour. The value of the storage modulus increases with an increase in the dispersed-phase concentration. The storage modulus data are interpreted in terms of the Princen and Kiss equation. Received: 23 October 1998 Accepted in revised form: 18 February 1999