(A) study on the morphology evolution of polymer blend in an electric field

Abstract

In this study, the morphology evolution of immiscible blend of polystyrene and poly (vinylidene fluoride) in a DC electric field was investigated. The effect of surfactant was considered by adding the block copolymer of polystyrene and poly (methyl methacrylate). The theoretical investigation was also performed to examine the effect of surfactant on the shape deformation and stability of a droplet suspended in an infinite immiscible fluid under uniform electric field, when the convection and diffusion of surfactant at interface were balanced. The domain perturbation was utilized to linearize the nonlinear free boundary problem and obtained the steady drop-shape in a uniform electric field. In stability analysis, the critical Weber number ($We_c$), which is a limit point for existence of the steady drop-shape, was estimated by transforming the We-perturbation into $P_2$-perturbation. In the limit of small deformation, the degree of deformation was in proportional to the electric field strength as predicted from theory. From this, the interfacial tension between two phases of polymer solutions was estimated. The theoretical and experimental results showed that the presence of surfactant made the drop more deformable and unstable. According to stability analysis, there was a critical Weber number above which the drop shape became time-dependent, and further increase in the electric field strength eventually break up the drop. The theoretical and experimental study were consistent in a qualitative manner. The primary mode of drop breakup was tip streaming and for the larger drop the fracture occurred simultaneously.