Glassy dynamics and nanoconfinement: what we learned, what comes next.

Over the past three decades, spatial confinement has reshaped our understanding of polymers as glass-forming materials. Rather than merely perturbing bulk behavior, geometric and interfacial constraints introduce new length and time scales that actively transform materials response, underpinning a range of otherwise distinct phenomena, from microscopic dynamics and macroscopic relaxation to vitrification and mechanical properties. By reducing at least one system dimension to the nanoscale, combined experimental, theoretical, and simulation efforts have revealed how confinement selects which dynamic modes remain active, uncovering relaxation pathways that might be silent in the bulk. These convergent insights have matured into a robust conceptual framework, which continues to evolve as new questions emerge. This perspective focuses on three themes that I consider central to this evolution: the decoupling of thermal and dynamical signatures of the glass transition under confinement, the emergence of finite low-frequency rigidity in confined liquids and soft solids, and the stabilization of long-lived nonequilibrium states mediated by interfaces and reduced dimensionality. The discussion of these topics points toward a necessary evolution: further progress will require theories that move beyond equilibrium descriptions to explicitly incorporate nonequilibrium pathways and emergent microscopic routes to macroscopic relaxation, ultimately bridging the gap toward a more complete, predictive description of glassy polymer dynamics.