Rheology and dynamics of water-in-oil emulsions under steady and dynamic shear flow

The fundamental aspects governing the rheology of water-in-oil emulsions, such as viscosity ratio and morphology were considered. The model developed here is based on the early work of Pal and Rhodes (1989) for viscosity equation, combined with the theory of Lee and Park (1994) for the morphological contributions. Thus, the proposed conception enables us to predict not only the degree of flocculation but also viscosity ratio and morphological effects. The contribution of secondary morphology caused by the flocculation of droplets on the viscosity of dispersed emulsions has been found by using the factor, -alpha'q'(xy)/y over dot (where alpha is the interfacial tension, q'(xy) is xy-component of anisotropy tensor, and y over dot is shear rate). However, this approach is only useful for system below the maximum random packing concentration. Experimentally, the bulk rheological properties have been examined under steady and dynamic shear flow to investigate the structure of emulsion. The flocculation-deflocculation transition was observed during the shear rate sweep, resulting in instant dilatancy of viscosity near the critical shear rate y over dot approximate to 100 s(-1). (C) 1997 Academic Press