Preparation And Properties Of Double Stimulus Responsive Liquid Crystal Elastomer Actuator

Liquid crystal elastomer(LCE)has raised increasing attention from scientists and scholars in recent years due to its multi-properties combined elastomer(entropy elasticity)with liquid crystal(self-organization)and ability to change its shape after applying external stimulus reversibly.After few decades of development,the stimulus-responsive LCE materials have been applied in many fields,such as valves in a microfluidic system,artificial muscle,propulsion system,smart surface,etc.In recent years,more and more stimuli-responsive LCE materials with complex deformations and wide application have been explored in depth.The application of traditional LCE materials are limited by the single deformation.Instead,more complex reversible three-dimensional deformation including spiral deformation has attracted increasing interest.Although most of the spiral structures are static and tend to exhibit irreversible one-handedness,the chiral reversal of spiral curl is often observed in nature.For example,to ensure more sunlight and living space,certain plants can adjust the chirality of spiral curling movements under external stimuli,such as light and humidity.Over the past few decades,a series of thermal-responsive and photo-responsive spiral LCE materials have been reported.The spiral curl can be achieved by tailoring the LCE film to different angles from the orientation direction.However,there is a significant disadvantage in that each film can only assume a single spiral under external stimulation.Therefore,we aim to develop a stimulus-responsive soft actuator with tuneable chiral spiral structure and motion pattern.Inspired by spiral-curled LCE materials and design of LCE soft actuators,a two-layer two-component photoresponsive LCE soft actuator was designed and fabricated.We integrated the trans-cis isomerization of azobenzene and the photothermal effect of a kind of near-infrared dye into a single LCE system.We completely superimposed two pre-crosslinked uniaxially stretched LCE films which contained different constituents in the same orientation direction,bonded them together by hydrosilylation reaction and cut at 45° with respect to the stretching direction.The chirality of helical curl motion could be switched by adjusting the wavelength of light.Specifically,a left-handed twist deformation occurs under the irradiation of near-infrared light(NIR),and a right-handed twist deformation occurs under ultraviolet light(UV)irradiation.The left-handed deformation could be completely performed within 5 s under NIR irradiation with a helix angle of 432° and a spiral rotation of 1.2,and the right-handed deformation could be completely performed within 45 minutes under UV irradiation with a helix angle of 162° and a spiral rotation of 0.45.Importantly,the two deformations are completely reversible.This tuneable photo-controlled chiral spiral LCE material has potential application in the fields of microfluidics,artificial muscles,and biomimetic devices.Additionally,azobenzene's trans-cis tautomerization effect and the hydrogen-based humidity effect were combined into one LCE system to prepare a UV/humidity double-stimuli-responsive LCE material.The multi-stimuli responsive behaviors are investigated under different external stimuli(UV,low/high humidity).The composite film are designed to realize a reversible three-dimensional deformation(bending)under UV-light irradiation and a reversible three-dimensional deformation(chiral spiral)in dry/wet environment,which might have potential applications in control devices and biomimetic devices,etc.