Collaborative Research: Connecting the Wetting and Rheological Behaviors of Compatibilized Polymer Droplets in Immiscible Polymer Melts

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TECHNICAL SUMMARY:The objective of the research is to elucidate and quantify how the wetting of diblock copolymers governs the dispersion of polymer droplets in immiscible polymer blends. Specifically, monodisperse polydimethylsiloxane-polyisoprene (PDMS-b-PIP) diblock copolymers will be synthesized, and these components will be added to immiscible blends of PDMS and PIP to formulate of well-defined model systems of PDMS/PMDS-b-PIP/PIP. The advantage of using these systems is that the coalescence of the droplets, which depends on the amount of copolymer at the droplet interface, can be studied in either the PDMS or PIP matrices, which are both melts at room temperature. The use of these components will help to establish whether wetting phase diagrams, which depend on the chain lengths of the block copolymers and matrix polymers, can be used to predict the rheology of the immiscible droplets. Specifically, can theoretically derived diagrams predict the regions over which droplets are unstable and coalesce or are stable and disperse? To explore this question, well-controlled rheological experiments will be performed on the model systems, and the results of these experiments will be compared to theoretical predictions of the rheological behavior of immiscible droplets in polymeric media. It is expected that the results of this research will enhance the understanding into the mechanisms that control the dispersion of polymer droplets into polymer melts. These findings should positively impact the production of engineered materials whose properties are optimized when the droplets are evenly dispersed throughout the blend. NON-TECHNICAL SUMMARY:Tremendous opportunities exist for researchers to create advanced, lightweight materials from immiscible polymer blends made compatible with block copolymers. Copolymers, containing blocks chemically identical to the blended components, segregate to the interface between the polymers, which should produce a fine dispersion of one polymer in another. However, fine dispersions are rarely achieved in practice, because the droplets tend to coalesce, weakening the performance of the blends. To resolve this issue, researchers from the University of Virginia (UVa) and Virginia Polytechnic Institute (VPI) will collaborate. They will synthesize and formulate systems of immiscible polymers and block copolymers of academic and industrial interest, and investigate the dispersion characteristics of these systems in well-controlled experiments. A central thrust of the research is to determine whether theoretically derived phase diagrams can be used to predict the regions over which the droplets coalesce or disperse. Preliminary findings of the collaborators indicate that phase diagrams do aid in the prediction of droplet coalescence and dispersion. Funding from the NSF will be used to cement these relationships, which are important because they can be used to provide user-friendly roadmaps to engineer advanced materials such as automotive parts, medical fabrics, and insulation products. Moreover, broader impacts from the research include using the results to enhance a course on interfacial chemistry and reaching out to local schools with the goal of increasing the number and diversity of qualified engineering and science applicants to UVa and VPI.