Sunlight helps self-healing of liquid-crystalline gels of lignin-graft PMMA doped with GO and azobenzene

Self-healing soft matters have attracted much attention because of their extraordinary performance for extending working life of materials. To utilise sunlight to help self-healing of liquid-crystalline gels composed of one low-mass liquid crystal (5CB) and one hyperbranched polymer (lignin-graft-PMMA), a low content of graphene oxide (GO) and one azobenzene compound are doped as photoresponsive additives. Upon irradiation of UV light, the azobenzene can induce gel-sol transition due to the photoinduced molecular cooperative motion, thus surface dents can be repaired. On the other hand, GO functions as the nanoscale heat source because of the photothermal effect under exposure of visible (VIS) or NIR light, heating the gel to undergo gel-sol transition for mending surface cracks. In addition, the mechanical properties of the gels are also improved by addition of GO. This NIR-VIS-UV light responsive liquid-crystalline gel shows highly effective gel-sol transition upon direct solar radiation because of the coexistence of both photochemical and photothermal effect. Furthermore, these sunlight-assistant self-healing gels also show anisotropy and orientation just like other liquid-crystalline materials, enabling them to find various advanced applications with longer service life.