INFLUENCE OF ELASTIC PROPERTIES ON DROP DEFORMATION AND BREAKUP IN SHEAR-FLOW

In this article we report experimental results on the deformation and the critical breakup conditions of a single drop in a medium under sim ple shear flow. The role played by both drop and matrix elasticities i s quantified by using constant viscosity elastic (Boger) fluids. The e xperiments were conducted using two transparent parallel disks mounted on a R-18 Weissenberg rheogoniometer. The critical shear rate was det ermined by imposing successive small changes in shear rate from lower to higher values until the drop breakup was observed. The results show remarkable differences in the mode of deformation and breakup for New tonian and elastic fluid systems. It is also found that the drop resis tance to deformation and breakup increases with increasing elasticity ratio. The contribution of the drop and matrix elasticities is quantif ied by using an empirical relation established between the drop deform ation and the capillary number, Ca. The critical breakup conditions, s uch as a dimensionless breakup time, t(b), and a critical capillary n umber, Ca-c, are determined as a function of the drop/matrix elasticit y ratio, k'. The values of Ca, and t(b) are found to increase with in creasing k'. (C) 1998 The Society of Rheology. [S0148-6055(98)00106-0] .