Droplet Breakup and Shear-Induced Mixing in Critical Polymer Blends

Abstract

Phase-contrast microscopy, small-angle light scattering, and fluorescence microscopy have been combined in situ to study domain deformation, breakup, and homogenization in unstable mixtures of polystyrene (PS) and polybutadiene (PB) under shear flow. Close to the critical point, mixing of the two components toward a single homogeneous phase occurs via repeated deformation and fragmentation of minority-phase droplets, and the data are in good agreement with the mode-coupling renormalization-group (MCRG) theory of a simple binary mixture under shear flow. Well into the two-phase region of diluted high-molecular-weight PS/PB blends, however, the data suggest a tendency for T c(γ) to saturate at very high shear rates.

String Formation in Sheared Polymer Blends: Coalescence, Breakup, and Finite Size Effects

“…The situation is more complex in concentrated dispersions where droplet coalescence and breakup occur simultaneously, however a 0 still defines a length scale for the maximum stable droplet size [7,8]. Stringlike structures have been observed in blends which are thermodynamically near a phase transition point [9][10][11][12] and in immiscible viscoelastic systems in complex flow fields [13]. While these studies focus on bulk behavior ͑a 0 ø d͒, a two-dimensional simulation has studied the influence of the walls [14].…”

Vorticity Elongation in Polymeric Emulsions

“…When a fluid dispersed in a second fluid is subjected to shear, the droplets deform and burst, and the use of shear flow to emulsify immiscible liquids is ubiquitous in the processing of soft materials. Although the pioneering work of Taylor [1][2][3][4] on isolated Newtonian emulsions remains at the foundation of our understanding, with the underlying intuition that the droplets elongate along the direction of flow at sufficiently high shear rates, the shear response of fluids that exhibit rheological complexity, such as semidilute entangled polymer solutions [5][6][7][8], wormlike micelles [9], and thixotropic clay gels [10], suggests that the shear can induce domains with extended correlation along the direction of vorticity, perpendicular to the flow field. In this Letter, stroboscopic video microscopy is used to measure the shear response of dilute emulsions composed of viscoelastic polymer melts.…”

Phase behavior of blends of poly (vinyl methyl ether) with styrene-acrylonitrile in film

“…As the phase separation takes place from the initially homogenous stage, the so-called ''spinodal ring'' [7] does not emerge. In fact, the pattern is a ''two-wing'' [8], just as the SALS pattern for blend under shearing, and the shear rate is relatively low [7,9]. Finally, the pattern becomes circular gradually as the phase separation proceeds.…”

“…Other works [7,9,18,19,20] have found the shear-induced orientation of polymer blends. In our study, both the coalescence and the orientation are found in 20/80 SAN99/PVME blend, so there must be some shear.…”