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

Abstract

Molecular motion in polymers is frozen below the glass transition temperature T_{g} and changes of viscoelastic functions are most spectacular near T_{g}. 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 T_{g} by light absorption. Relaxation processes, which take decades to centuries in some high-T_{g} polymers, are reduced to minute timescales by sub-T_{g} 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.