Journal of Rheology, Vol.54, No.6, 1285-1306, 2010
Droplet dynamics in mixed flow conditions: Effect of shear/elongation balance and viscosity ratio
The dynamics of single droplets dispersed in a second, immiscible liquid undergoing a controlled mixture of shear and elongational flow has been studied using a home made eccentric cylinder device. The model system consists of poly(dimethyl siloxane) droplets in a poly (isobutylene) matrix, both Newtonian liquids at room temperature. In continuation of previous work [Boonen et al., Rheol. Acta 48, 359-371 (2009)], the effect of changing the balance of shearing and elongational flow components and varying viscosity ratio on the deformation and orientation of the droplets has been systematically investigated under sub-critical flow conditions. The experimental results obtained from optical microscopy are compared with theoretical predictions of the phenomenological model by Maffettone and Minale [J. Non-Newtonian Fluid Mech. 78, 227-241 (1998)], obtained using the transient form of the model and incorporating a flow type parameter that accounts for the relative amount of extension in the flow. Overall, a fair agreement was found between the model predictions and the experimental results for all sub-critical mixed flows applied and all viscosity ratios investigated here. This work provides an experimental reference data set which can be used to guide future modeling efforts. (C) 2010 The Society of Rheology. [DOI: 10.1122/1.3490661]