Tg Changes, Surface Effects, and Dynamics in Nanoconfined Polymers

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TECHNICAL:The fundamental question of confinement and surface effects on material behavior at the nanoscale, and in particular the glass transition (Tg) and related dynamics, will be addressed using a model thermosetting material confined to various nanoconfining geometries, including freely-standing and supported thin films, rods, and spheres. The relative contributions of surface and intrinsic size effects will be systematically varied since the scaling of the surface area to volume as a function of nanoconfinement length scale differs for different geometries. Model polycyanurate materials will be used in the study because they allow annealing of residual stresses without dewetting or hole growth problems and allow facile synthesis of both freely-standing, as well as supported structures. The effect of crosslink density on the Tg depression will be examined in order to test recent suggestions that molecular stiffness and size of the cooperatively rearranging regions are important factors for determining the magnitude of the Tg changes. The glass transition temperature will be measured using differential scanning calorimetry (DSC) as a function of cooling rate, and dynamics will be measured using a new method for measuring the linear dynamic specific heat using quasi-isothermal DSC.NON-TECHNICAL:The properties of polymers in thin films and other special geometries are going to be studied in the solid state by a variety of experimental techniques. The results of the research are important for a fundamental understanding of nanoscale behavior and to test recent hypotheses for this behavior. In addition, the results are important to electronic and aerospace industries since they will facilitate optimization of polymer properties in nanoelectronic, nanolithographic, and nanocomposite applications. The proposed work includes the training of two graduate students and an undergraduate researcher in cutting edge research involving polymer chemistry and physics at the nanoscale and calorimetry. Ethics training will be incorporated into the training of the students. The PI has a strong track record working with minority and female students, and a strong effort will similarly be made to include underrepresented students in this project. Outreach will include development of a one-week long polymer module for the TTU program, "Science - It's a Girl Thing," for girls in high school, and the development of four two-hour modules for the TTU Super Saturdays science program for 4th to 6th graders.