Interfaces have long since been known to alter local dynamics of materials with glasses exhibiting outsized effects presumably because their dynamics appear to be particularly sensitive to small changes in local packing. Our group has focused recent efforts on investigating how the local glass transition changes across interfaces between two polymers with widely different bulk glass transition temperatures Tgbulk. Starting with a single interface between two semi-infinite domains (ΔTgbulk ≈ 80 K), we have used a localized fluorescence method to demonstrate broad profiles in the local glass transition temperature Tg(z) across dissimilar polymer-polymer interfaces spanning hundreds of nanometers and observed to be asymmetric relative to the composition profile. In these materials, the geometry of the morphology creates glasses where the dynamical heterogeneity has a strong directional gradient. A key finding of these results is the observation that the broad coupling of dynamics across the dissimilar polymer-polymer interface only occurs if this interface is annealed to equilibrium. Our efforts to understand what factors during polymer interface formation causes these broad profiles in Tg(z) find that chain connectivity appears to be surprisingly important. This is confirmed by studies on silica substrates with tethered chains where low grafting densities (~10 vol% tethered chains) are observed to cause large +50 K increases in local Tg. We now explore what property changes take place in multilayer systems during interface annealing that alter dynamics across the material using different experimental techniques with the goal of understanding what controls dynamical coupling across dissimilar polymer domains and how interfaces mediate this behavior. Advanced materials design is headed towards increasing amounts of interfaces with progressively smaller domain sizes where the geometrical arrangement of these interfaces can be utilized to alter local material properties for desired applications.

Uncovering factors causing dynamic coupling across dissimilar polymer domains

2019 Spring National Meeting

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