Interfaces impact the properties of glasses over surprisingly large length scales, which has important implications for developing nanoscale devices involving polymers. Emory graduate student Yannic Gagnon, together with his PhD advisor Prof. Connie Roth and Prof. Justin C. Burton, recently discovered a new mechanism for how local dynamics in glasses may be coupled over long distances by the way sound waves can propagate across the material, reflecting at or transmitting across interfaces, and interacting with the vibrational spectrum of density fluctuations. By measuring shear wave propagation across glassy polystyrene and rubbery polybutadiene bilayer films, they demonstrated the emergence of a long range 200 nm gradient in local modulus when the interface between the glassy and rubbery polymer domains is formed. This work also suggests a new way to understand long range profiles in local glass transition temperature Tg that have previously been measured in these systems.
Development of broad modulus profile upon polymer–polymer interface formation between immiscible glassy–rubbery domains, Proceedings of the National Academy of Sciences, December 2023, DOI: 10.1073/pnas.2312533120.