Isothermal Compressibility of Azobenzene-Containing Epoxy-Amines Measured Using Small-Angle X-ray Scattering

The fracture behavior of polymers shifts from a brittle to ductile response as the environmental temperature cycles from below to above the glass transition temperature (T_g). The ability to rapidly transition through a T_g-like response using an external stimulus is a proposed mechanism by which mechanical properties of a polymer could be temporarily switched, depending on the needed response of the material. This capability could allow a strong, high-T_g polymer with the ability to “switch-on” T_g-like motions when desired. One method for inducing a T_g-like response may be the introduction of molecular motion in the glassy polymer through azobenzene isomerization. Azobenzene isomerization, which is a light-triggered molecular motion, may be sufficient to locally deform the network and encourage long-range chain cooperativity, and thereby transform the glass into a rubber. Isothermal compressibility, an intrinsic materials property often considered to be the inverse of elastic modulus, would be expected to increase if illumination causes the material to soften due to photoisomerization of azobenzene. In this presentation, results will be presented from a recent study in which small-angle X-ray scattering (SAXS) was used to measure isothermal compressibility of azobenzene-containing epoxy-amine networks with and without UV illumination