When 9:00 AM - 11:00 AM Jan 11, 2018
Where NCRC Bldg. 10, Room G063
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PhD Dissertation Defense: Relaxations in Complex Polymer Systems

Ravi Sharma
MSE PhD candidate

Polymers are used in a variety of applications, from energy conversion and storage to membranes for gas separation and organic electronics. A key challenge for the design, processing, and performance of these materials is to understand interrelations between physical properties and the local and macro-scale morphologies. This thesis was devoted to understanding the role of morphology on chain relaxation and transport processes in different intermolecular environments encountered in different applications.

In bulk, miscible A/B polymer/polymer blends, unlike small molecule mixtures, the composition is homogeneous at the macroscopic scale, yet spatially heterogeneous at the molecular level. We show that this spatial compositional heterogeneity, in blends where the A component has a much lower glass transition temperature T9A<<T9B, has a profound influence on the relaxation and transport of the A chains. Below the blend glass transition temperature T9blend, the A chains relax at rates that differ by orders of magnitude, depending on the local composition in which they reside.

When the A/B blends are confined between two substrates over lengths-scales under a micron, one of the components may preferentially wet the substrates and strongly influence the composition as a function of film depth. Consequently, when component A enriches the substrates, the relaxation and transport of the A chains become film thickness dependent. Whereas thickness confinement effects modify the dynamics of pure homopolymers chains for thicknesses up to a few nanometers, the effects on these A/B blends extend over hundreds of nanometers.

In the final case, in which a polymer A is confined between a hard substrate C and a soft, immiscible polymer film B, the relaxation rates of A are significantly faster than the case where A is symmetrically confined between two substrates C. These findings implicate the sensitivity of polymer dynamics to the modulus of the confining environment.

These studies reveal that the relaxation and transport of polymers differ from their intrinsic behavior in different molecular environments, and provide new insights into the design and use of polymers for nanoscale application.