| Liquid crystal elastomer（LCE）as a kind of stimulus-responsive materials,which can prepare materials with complex three-dimensional（3D）shape changes,and has wide application prospects.According to the reversible shrinkage and expansion of the monodomain LCE along the director under external stimulation,the deformation of the vertically aligned LCE film is along the thickness（less than 200μm）,resulting in a small deformation.So far,LCE with the vertically aligned mesogens has seldom been reported except for trans-cis isomerism of the azo systems.Therefore,it is of great significance to obtain 3D shape change of the vertically aligned LCE designed by appropriate structures.In this thesis,we proposed a practicable and versatile method to fabricate a complex 3D deformable LCE based on vertically aligned monodomain with a cross-link gradient,and further applied it to the preparation of soft robots such as micro-walker.1. First,a class of gold nanoparticle vertical alignment agent（Au@TE-PDB） was synthesized,which was used to induce the vertical alignment of liquid crystal monomers and cross-linking by using its film-forming properties and good effect of inducing vertical alignment of liquid crystal molecules orientation.Then,in-situ photopolymerization was performed by ultraviolet light irradiation to obtain a vertically-oriented LCE film,which can cause a cross-linking gradient inside the LCE film.The resulting LCE film showed reversible bending deformation under thermal stimulation,instead of the stretching/contraction deformation exhibited by a typical monodomain LCE.The nanoindentation experiment demonstrated that the deformation of LCE films came from the difference in Young’s modulus on two sides of the thin film.In addition,simply scissoring the thin film was able to prepare the samples with different bending angles under the fixed length.Further,the cut along the diagonal of the film was used to simulate the blooming and closing of flowers.Besides,by using the bending deformation mechanism,reasonable control of the area and direction of ultraviolet light irradiation could realize the construction of complex3D deformation LCE,such as bending,folding and wavy.2. Since the above-mentioned stimulation methods for deformation were only implemented on the hot stage,it cannot be remotely controlled and it was difficult to achieve deformation of local area.Therefore,a photo-thermal molecules were introduced to construct light-responsive LCEs,and the above method was uesd to prepare wave-deformable LCEs for building micro-walkers.The carboxyl-functionalized carbon nanotubes were produced as initiators to initiate the polymerization of liquid crystal monomers,and liquid crystal polymer modified carbon nanotubes（CNT-PDB）were synthesized.The photothermal molecules showed good solubility,and the CNT-PDB and polymerizable liquid crystal mixture were thoroughly mixed and poured into a liquid crystal cell to prepare a light-responsive LCE film.The obtained LCE film had a vertical orientation,and it was able to rise temperature rapidly under the irradiation of near-infrared light and bend quickly.It was worth noting that the photoinduced deformation was same as the vertically oriented LCE described above,that is,a reversible,macroscopic bending deformation,and it can only bend toward one side.Finally,LCE films containing CNT-PDB and wavy deformation were prepared.By continuously moving the irradiation area of near-infrared light,the microwalker can quickly crawl and the speed reached 0.28 mm s-1,which successfully realized the construction of a micro-walker. |
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