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Predictive Design of Interfacial Functionality in Polymer Matrix Composites
Technical Report,01 Nov 2013,31 Oct 2016
University of Michigan Ann Arbor United States
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With this research we explore interfacial functionality in polymer matrix composites from sensing and monitoring of mechanical damage to the active control of interfacial phenomena, such as the transport of heat and mass. We use a combined computational and experimental approach. Structures generated using our simulation framework allow us to gain unprecedented insights into anomalous diffusion behavior of water in polyimides and reveal that non-bonding interactions play a more important role in the thermal conductivity of polymers than expected. At 20-30 of the nominal breakdown voltage we observe small changes in the elastic modulus of PVDF as a result of applying this field, but these changes dissipate with time. Closer inspection of the time dependence of elastic property changes under the influence of external constrains reveal that, as long as the deformation remains within the elastic regime, the elastic modulus gradually returns to the value that corresponds to the unstrained state, presumably as a result of structural reconstitution. Two different relaxation rates govern this process, and they differ by up to two orders of magnitude, depending on the amount of strain applied and the deformation history. The slower processes are only observable in the adiabatic modulus. These results provide insights into the relative magnitudes of entropic and enthalpic changes that occur upon deforming PVDF. We attribute theenthalpic changes predominantly to nonbonding interactions, since in the elastic regime we do not expect covalent bonds to rupture under deformation.
APPROVED FOR PUBLIC RELEASE