Ionic Conductivity Switchable and Shape Changeable Smart Skins with Azobenzene-Based Ionic Reactive Mesogens

To develop smart ionic skins capable of multi-responsiveness and switchable ionic conductivity, a stimuli-responsive and ionic conductive azobenzene-based monomer is newly synthesized, uniaxially oriented, and polymerized for anisotropic liquid crystal elastomers (LCEs). Since the uniaxially oriented monodomain LCE with ionic asymmetric azobenzene monomers (i-AAM) is prepared by thermal oligomerization, uniaxial stretching, and subsequent photopolymerization, the stimuli-responsive i-AAM LCE is thermally contracted by increasing the temperature above T_NI as well as is bent along the aligned direction by irradiating it with UV light. In addition to the change of shape, the ionic conductivity of the LCE is reversible in response to heat and light stimuli. Polydomain i-AAM LCE polymerized without the stretching process exhibits higher ionic conductivity than stretched monodomain LCE due to the initially formed stable ionic pathways. Ionic conductivity can also be switched simultaneously by polarity changes in response to the photoisomerization of i-AAM, increased mobility from heat, and an elastic mechanoresponse from external stresses. These i-AAM LCE-based soft grippers exhibit stimuli-responsive grasping and releasing actuation and detect ionic conductivity switches finely, suggesting potential as smart skins for advanced soft robots.