Viscoelastic and Photoresponsive Properties of Microparticle/Liquid-Crystal Composite Gels: Tunable Mechanical Strength along with Rapid-Recovery Nature and Photochemical Surface Healing using an Azobenzene Dopant

We investigated viscoelastic and photoresponsive properties of the microparticle/liquid-crystal (LC) composite gels. The mechanical strength of the colloidal gels can be widely tuned by varying particle concentrations. With increasing particle concentration, a storage modulus of the particle/LC composite gels increased and reached over 10(4) Pa, showing good self-supporting ability. We demonstrated for the first time that the particle/LC composite gels exhibited rapid and repetitive recovery of the mechanical strength after large amplitude oscillatory breakdown. In addition, photoresponsive properties of the composite gels were investigated by the cis-trans photoisomerization of the azobenzene compound doped into the host LCs. The photochemical gel-sol transition could be repeatedly induced by changing the phase structure of the host LCs between nematic and isotropic, using the photoisomerization. The particle/LC composite gels can be applied to optically healable materials by the site-selective gel-sol transition based on the photochemical modulation of the phase structures of the host LCs.