(324e) Confinement Effects On the Glass Formation Behavior of Nanolayered Polymers

Confinement to nanoscale dimensions produces large changes in the engineering properties of glass-forming materials. Until recently, the majority of studies on nanoconfinement effects on the glass transition have focused on freestanding films and films supported by rigid substrates. In contrast, many real-world materials exhibit internal nanoconfinement: they possess distinct polymeric domains of nanoscale dimension confined between mutual interfaces. Examples include block copolymers, multi-nanolayered polymers, polymer nanoblends, and bulk heterojunction organic photovoltaics. In this presentation, I will describe recent and ongoing work in our group employing computer simulations to characterize and understand nanoscale confinement effects in such a system – a nanolayered polymer.

Our results show that the glass formation properties of nanostructured polymers depend strongly on both the relative T_g of the nanoscale polymer domains and the degree of immisibility of the polymers. We also observe confinement-induced changes in the ‘fragility’ of glass formation, which quantifies the ‘abruptness’ with which the glass forms on cooling. Results indicate that these changes are neither a direct result of interfacial mixing nor of a change in free volume at the interface, but rather emerge from changes in interfacial mobility parallel and normal to the interface. These changes are hypothesized to be controlled by dynamic coupling across the interface, resistance of the interface to penetration by chains, and the inherent susceptibility of each polymer to dynamical perturbations as quantified by their fragilities of glass formation. These studies suggest a new basis for understanding and controlling glass formation behavior in nanostructured polymers via rational selection of polymer bulk and mixing properties.