Particles at polymer/polymer interfaces: Interfacial phenomena and morphology control in immiscible polymer blends

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

09329091 Velankar Particles that are partially wetted by oil and water are well known to adsorb at oil/water interfaces. Such interfacially adsorbed particles can stabilize emulsions of oil and water, and these emulsions are called Pickering emulsions. We seek to transplant this idea of Pickering emulsions to polymeric systems: specifically to create stable morphologies composed of two immiscible homopolymer phases and interfacially adsorbed particles. Previously we have shown that particles readily adsorb at the interface between a variety of polymers, and that even a small fraction (well under 1 vol. %) of particles can greatly affect the morphology of droplet/matrix polymer blends. Furthermore, when particles are sufficiently crowded at the interface, they jam the interface into a solid like state that prevents interfacial tension driven changes of the morphology. Here we propose a comprehensive experimental study of the effects of interfacially active particles in immiscible polymer blends. We hypothesize that particles that adsorb at the interface between two immiscible homopolymers can be used to control the morphology of the blend, in particular they can control the sizescale of the morphology, create highly anisotropic (cylindrical or lamellar) morphologies, as well as generate a new type of layered structure. Research Proposal: Experiments will be conducted on a model pair of homopolymers,(crosslinkable polyisoprene (PI) and polydimethylsiloxane (PDMS)), and silica particles that are surfacemodified to adsorb at the PI/PDMS interface. In situ flow visualization experiments will be conducted under shear flow conditions to characterize the morphology. Particle scale imaging will be performed ex situ by crosslinking the PI, washing away the uncrosslinked PDMS, and then conducting SEM of the particle laden interface. In initial research, we will devise flow protocols that induce the particles to rapidly adsorb at the interface, and induce them to crowd at the interface to cause interfacial jamming. We will also examine whether particles aggregate or spread on the interface, and whether they reduce the interfacial tension. The core of the research then is to test the above hypothesis about morphology control. The effect of particles on the flow induced morphology will be examined as a function of the relative volumes of the PI and PDMS, the particle loading, and the wettability of the particles. The ability of the particles to control the sizescale of the morphology and their ability to stabilize anisotropic morphologies by interfacial jamming will be examined. Finally, at high particle loadings when the particles tend to form layers in shear flow, we will examine whether these particle layers can template a PI/PDMS alternating lamellar morphology. Intellectual merit: This proposal unites knowledge in three different areas: interfacially adsorbed particles in oil/water systems, polymer compatibilizers at polymer/polymer interfaces, and the flow induced morphology in polymer blends. These ideas are combined together to develop particulate compatibilizers particles that act as interfacial modifiers in polymeric systems in a fashion similar to block copolymer compatibilizers. Such particulate compatibilizers have the potential for achieving morphology control far beyond what is possible with conventional block copolymer compatibilizers. During the course of this research, we will also address several practical and fundamental issues such as how to rapidly adsorb the particles on the interface, and whether particles reduce the interfacial tension of polymeric interfaces. Finally, the PI has had success with transplanting several concepts from oil/water systems to polymeric systems, and this proposal goes considerably further in that direction. Broader impact: This proposal will develop a new mechanism to precisely control the morphology of polymer blends, and develop a new type of particle templated morphology composed of alternating layers of two immiscible polymers with particles at each interface. One graduate student and several undergraduates will be trained. The PI will develop a new hour long undergraduate level module on wetting phenomena for engineers combining hands on experiments with theoretical discussion. This is a part of a series of modules on soft matter that will be made available publicly.