Kinetics of Photoisomerization of Azobenzene at Surface of Glassy Polymers

The design of responsive surfaces of polymer glasses with rapidly switchable properties remains a challenge due to the restricted mobility of the glassy polymer chains, which limits the dynamics as well as the responsiveness. However, recent studies have revealed that the surfaces of polymers exhibit active dynamics even at temperatures far below the glass transition temperature. In this work, we constructed an azobenzene-functionalized surface of glassy polystyrene (PS) and measured the photoisomerization of surface azobenzene using dynamic wetting measurement. Notably, the azobenzene isomerization rate at surface is indistinguishable from that in solution and is 10 times faster than that in the glassy bulk, revealing a "liquid-like" surface in terms of photoisomerization on polymer glasses. This was presumably attributed to the reduced energy barrier and enhanced mobility at the surface. These findings offer new insights into the understanding of the photoisomerization of azobenzene groups at the surface of glassy materials.