CAREER: The Role of Relative Motion and Intermolecular Ordering on Dynamic Behavior of Polymers and Polymer Blends

The objectives of this research project are to (1) correlate relative motion in relaxation processes of glass-forming polymers with the character of inter- and intra-molecular packing, and (2) assess the way in which intermolecular packing changes as a function of environment and the relation of these changes to know relaxation behavior in blends. The importance of the spatial region corresponding to the preferred intermolecular packing distance has previously been demonstrated. However, not all polymers have similar degrees of intermolecular ordering, and the effect of this on dynamics is unknown. Further, intermolecular ordering shifts depending on environment, and the effect of this is unknown as well. To achieve the objectives stated above, a series of polymers, wherein the degree of intermolecular ordering ranges from very little to extensive will be considered. A given polymer [A] will then be considered in a series of second components [B]. Changes in the degree of intermolecular ordering will be observed, including the original polymer [A-A], and the new ordering [A-B} induced by the changing environment. Observations will be made by coherent neutron scattering, which reveals relative motion on selected spatial scales, and molecular simulation, will assess the location and extent of spatial separations relevant to interchain packing. This combination of techniques has been chosen because they can follow relative motion with spatial selectivity. The ability of neutron measurements to select for spatial scales will be exploited to separate the contributions of the a and b-relaxations, and assess the influence of environment of each individually. The novelty of the proposal lies in following relative, rather than self motion, investigating carefully selected series of materials, and integrating molecular simulation. This work, when completed, will allow us to connect features intermolecular packing with relative motion, and to unambiguously delineate the role of environment in miscible blend dynamics.

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Educational activities are centered on bringing research-oriented activities to students who would not otherwise have these experiences. Specifically, open-ended experimental/simulation problems will be introduced in core chemical engineering courses, research opportunities will be provided to students in non-research universities, and a senior elective course on molecular simulation and its role alongside experiment will be added to the Chemical Engineering curriculum. Selected undergraduate students entering their senior year at Cal Poly Pomona, and industrially oriented university with no formal research program, will be invited to spend a summer pursuing research in the PI's group. The students' research will continue as their senior thesis project during their final year. These students will develop a course project based on the research they conduct at Penn State. At the same time, open-ended projects will be developed and used in the reaction engineering and thermodynamics courses, and an experiment with a simulation comp0nent will be added to the senior laboratory course. These projects will be compiled, and in the last year of the Plan, used as modules in a senior elective course. This course, aimed at non-simulators, will teach students how to use and interpret simulation data, much as a traditional laboratory course does the same for experimental data.

The research to be carried out in this proposal falls in the general area of short-time dynamic behavior in polymer melts and blends, an area important for its relevance to the glass transition and processing behavior of these common materials.