Model for athermal enhancement of molecular mobility in solid polymers by light

Abstract

Molecular motion in polymers is frozen below the glass transition temperature Tg and changes of viscoelastic functions are most spectacular near Tg. Exceptional enhancement of molecular mobility and a decrease of polymer viscosity, by several orders of magnitude, down to the viscous flow regime, are observed way below Tg by light absorption. Relaxation processes, which take decades to centuries in some high-Tg polymers, are reduced to minute timescales by sub-Tg light absorption. Here we develop a model for this intriguing albeit spectacular action of light on glass forming materials and we propose experiments to relate light absorption to materials properties. The model provides a solution to a long-lasting problem of how molecular mobility is enhanced in solid polymers by photoisomerization and provides a tool for a better understanding of the relationship between light absorption and material properties and developing photosensitive polymers for light to mechanical energy transduction.