Large <i>T_g</i> shift in hybrid Bragg stacks through interfacial slowdown

Studies of glass transition under confinement frequently employ supported polymer thin films, which are known to exhibit different transition temperature T_g close to and far from the interface. Various techniques can selectively probe interfaces, however, often at the expense of samples designs very specific to a single experiment. Here, we show how to translate results on confined thin film T_g to a 'nacre-mimetic' clay/polymer Bragg stack, where polymer molecular layer number is precisely tunable. Exceptional lattice coherence multiplies signal manifold, allowing for interface studies with both standard T_g and broadband dynamic measurement. For the monolayer, we not only observe a dramatic increase of T_g (~ 100 K), but also use X-ray photon correlation spectroscopy (XPCS) to probe platelet dynamics originating from interfacial slowdown. This is confirmed from the bilayer, which comprises both “bulk-like” and interface contributions, as manifested in two distinct T_g processes. Since platelet dynamics of mono- and bilayers are similar, while segmental dynamics of the latter are found to be much faster, we conclude that XPCS is sensitive to the clay/polymer interface. Thus, large T_g shifts can be engineered and studied once lattice spacing approaches interfacial layer dimensions.