The Light-Controlled Color-Changing Performance And Tunable Motion Modes Of Liquid Crystalline Elastomer Soft Actuators

Liquid crystalline elastomers(LCEs)as the classical two-way shape memory material,possessing many technical advantages such as ease of functionalization,low weight,multiple degrees of freedom,have been applied to soft actuators,artificial muscle,biomimetic devices,manipulators and so on.In this thesis,a variety of functionalized LCE materials have been synthesized to fabricate smart actuators.The synergistic color-changing property and the method of stimuli-controlled shape morphing,mode of motion and the potential applications in biomimetic devices and robotic technology of these LCEs have been studied in depth.The main research content and innovation can be divided into three parts:1.In this thesis,two spiropyrane molecules possessing different thermochromic properties have been synthesized and chemically bonded to an organic dye doped LCE matrix,to fabricate a series of multi-color-changing artificial flowers.Relying on the combination of photochromic effect,thermochromic effect,pigment blending effect,photothermal conversion effect,and gradient stress effect,the multi-stimuli responsive behaviors of this artificial flowers are investigated under the stimulation of near-infrared light(NIR),ultraviolet(UV)and green light.Taking the organic dye Green 575 doped artificial flower as an example,in the irradiation by UV light,the color of petals is murrey;when exposed to NIR light,a blooming “flower” can furl into buds with colour changing from murrey to red brown,reopen the petals to produce a red brown blooming “flower” after removal of NIR light,finally change the petal colour to green under the irradiation of green light.Such a material capable of multi-color-changing property and synergetic bending function,has wide application prospects in camouflage materials,controlling and biomimetic devices.2.Different photothermal dyes with separate absorption regions are embeded into different layers of LCE materials to build multiple independent and non-interfered photothermal conversion systems responding to different wavelength bands of light.A series of multi-stimuli-responsive hierarchical structured LCE soft actuators capable of performing not only multi-directional moving,but also different shape morphing modes are fabricated.In this thesis,three organic NIR absorbing dyes,YHD796,commercially available Dye1002 and Disperse Red1 which have sharp and almost non-interfered absorptions around 796 nm,1005 nm and 512 nm respectively,are doped into LCE materials to fabricated a trilayered TLCE actuator and bilayered two-way or multi-bidirectional moving actuators.The multi-stimuli responsive behaviors of these actuators are investigated under the stimulation of near-infrared light(808 nm,980 nm),green light(520 nm).Such a TLCE film can be stimulated by two NIR sources(808 nm,980 nm)to execute downwards bending/upward bending or right-handed helical twisting//upward bending,respectively;under the combinatorial stimulation of 520 nm,808 nm and 980 nm light,the multi-directional walker robot can move forward/backward,turn left/right without any special controlling.It means that the controlling of multi-directional moving and diversified shape morphing modes of soft actuators can been realized by modulating the wavelength of stimuli light,which overcome several disadvantages(such as limited light penetration capability,very slow UV-responsive rates)resulting from the multi-stimuli system consisting of visible/infrared(vis/IR)-triggered photothermal-induced phase transition effects and UV-induced trans-cis isomerization of azobenzene chromophores.In addition,our design may greatly improve the moving controlling method of soft actuator and have wide application prospects in controlling devices.3.In topological field,M?bius strip is the classical one-sided surface toroidal sample with unique geometrical features,which has inspired mathematicians,physicians,chemists,engineers and artists for many centuries;whereas other toroidal ribbons with an even number of twists showing two sides and two edges are classified as “twisted ribbons”.Due to the twisted toroidal conformation,M?bius ribbons and twisted ribbons have considerable torsional strains,and the highest bending/torsional energy is distributed around the locus of twist region,based on previous study.This interesting phenomenon inspires our imagination:if a M?bius ribbon or twisted ribbon was prepared by some stimulus-responsive polymeric material,applying stimuli on the locus of twist region might release the accumulated torsional energy,break the energy localization equilibrium,and further induce an autonomous rotation.In this thesis,a series of single layered M?bius ribbon(S-M?bius[+1]),twisted ribbon(S-M?bius[+2])and bilayered twisted ribbon(B-M?bius[±2])actuators are fabricated by using functionalized LCE material.The mode of motion of these actuators are investigated under the stimulation of NIR light.Under the irradiation of 808 nm light,S-M?bius[+1] and S-M?bius[+2] can only shrink and wrinkle,whereas B-M?bius[±2] can been stimulated to rotate around a diameter-matched circular cylinder(d = 5.0 mm).This work may pave the way in developing soft actuators with unique geometries and macroscopic motions.