Invited: Glass transition of polymers under ultrafine nanoconfinement: interfacial dynamics and the spatial gradients*

Polymers under nanoconfinement can exhibit large alterations in dynamics or mechanical properties from their bulk values. These large changes in properties impact strongly the macroscopic properties of multicomponent or multiphase polymeric materials that have been widely used for engineering applications. The large influence of the nanoconfinement has often been attributed to an interface effect. However, the origin of the interface effect and its connection with the bulk glass transition remains a topic of active debate. In particular, a spatial gradient in polymer dynamics near an interface has been widely acknowledged. On the other hand, experimental characterizations of the interfacial dynamics gradient remain rare, hindering an in-depth understanding of the interface effect and its relationship to the nanoconfinement effect. In this contribution, we prepare ultrathin polymer films of ~10 nm in thickness and perform systematic dynamics measurements through broadband dielectric spectroscopy. The structural relaxation over a wide temperature range will be presented. The glass transition of these ultrathin films will also be discussed in detail, with a special focus on the spatial gradient of interfacial dynamics and its relationship to the glass transition.