Drop deformation in polymer blends during elongational flow

An original method for measuring droplet deformation in polymer melts during uniaxial elongational flow has been developed. It is based on the observation of a limited number of drops, before and after elongation in the melt. The shape of the elongated drops was frozen by fast quenching. Two PS samples for the continuous phase, plus two HDPE, and one PMMA for the drops, allowed a wide range of viscosity ratios (0.0046 < p < 13). Experiments at high capillary number (Ca) values were in good agreement with Taylor's linear newtonian theory up to deformations of about λ = 4: viscous drops (p > 1) deform less than the surrounding matrix, whereas the opposite is observed for low viscosity drops (p < 1) with a limiting ratio of drop vs. matrix deformation of 5/3 at vanishing drop viscosity. Experiments carried out at Ca values of the order of unity showed that the drop deformation increases linearly with their initial radius in agreement with the linear theory. In some cases, the agreement with the data could be improved by using Palierne's theory for viscoelastic systems. Analytical expressions could be obtained for maxwellian fluids and high capillary numbers.