Capillarity, Wetting, and Rheology in Multiphase Particle-filled Polymer Blends

Prof. Sachin Velankar

Dept. of Chemical Engineering, University of Pittsburgh, USA

时间: 5月24日（周四）下午2点

地点：英士楼201会议室

联系人：谢续明

Abstract👩🏽‍🎓：

Particle-filled polymers are very common in practical applications ranging from nanocomposites, packaging films, to rubber tires. Blends of immiscible polymers are commonly used in a variety of applications as well, such as rubber toughening or improving the barrier properties of polymers. Here we examine situations where particles are filled into a blend of two immiscible polymers. The overall goal is to explore the rich composition-morphology relationship in these systems.

In such polymer/polymer/particle ternary blends, the microstructure resulting from the blending process arises from a coupling between three factors: (1) capillarity, i.e. the tendency to minimize interfacial area between the immiscible polymers, (2) wettability, i.e. the relative preference of the particles for each polymer, and (3) viscous forces required for mixing. We examine the morphology and the rheological properties of ternary mixtures of particles (30 vol%) and two immiscible molten polymers, polyisobutylene (PIB) and polyethylene oxide (PEO). The particles are fully-wetted by PEO, and the fraction of the fully-wetting liquid ranges from very small to large values.

Morphological characterization reveals a sequence of morphological changes as the composition is varied: PEO meniscus-bound particle aggregates at low wetting fluid fraction, cocontinuous morphologies when the two polymers have comparable fraction, and a "drops-in-suspension" microstructure at high wetting fluid fraction. Rheological characterization by small and large amplitude oscillatory shear, and by stress ramp experiments reveals that many of these mixtures have solid-like rheology with yielding at high strain. The solid-like behavior (quantified by the low-amplitude storage modulus or the yield stress in a stress ramp experiment) is highest for meniscus-bound aggregates; this is in contrast to particle-free mixtures in which cocontinuous morphologies tend to show the greatest solid-like behavior. We construct a microstructural map for such ternary blends in which the various morphologies and the phase inversion composition are mapped on a triangular composition diagram. With a clear understanding of the fundamental physics of such systems, it is possible to design new materials or new processing strategies. We will show two examples: one in which plastics are made conductive, and one in which porous ceramics can be made.

Sachin Velankar is an Associate Professor in Chemical Engineering at the University of Pittsburgh. He got his Ph.D. in Chemical Engineering from the University of Delaware in 1999. This was followed by post-doctoral fellowships in the Katholieke Universitiet Leuven and the University of Minnesota, after which he joined the University of Pittsburgh. He has research interests in a wide range of topics in soft materials including polymers, interfacial phenomena, thin film mechanics, hydrogels, and polymer foams.