Regulating Color Activation Energy of Mechanophore-Linked Multinetwork Elastomers

To lower color activation stress/strain while maintaining excellent mechanical properties for mechanochromic materials has been a challenge. Here, a structure of multinetwork polyacrylates was adopted to incorporate a widely studied mechanophore, spiropyran (SP), to investigate the regulation of mechanochromic sensitivity by varying network compositions. In situ color channel intensity analysis was used to characterize deformation-induced ring-opening of SP to merocyanine (MC) for color changes. The multinetwork strategy could substantially reduce the onset of mechanochromic activation strain and stress, and the resulted double networks and triple networks exhibited remarkable mechanochromic performance with excellent mechanical properties. The network formation conditions, including solvent ratio and type of monomers, were shown to have great impact on regulating the mechanochromic activities. A triple-network sample achieved the lowest macroscopic color activation energy compared to previously reported SP-linked elastomers. In addition, the ratio of SP to MC conversion activated by stretching was first shown higher than that by UV light.