The Preparation Of Micro-and Nanostructures With Azobenzene Liquid Crystal Elastomer

Azobenzene liquid crystal polymer has attracted much attention in the field of light-responsive polymer material because of its photoresponsive behavior and self-assembly property. Compared with ordinary liquid crystal polymer, the photoresponsive behavior of azobenzene has significant effect on the characteristics of the liquid crystal, such as photoinduced alignment, photochemical phase transition and photo-triggered molecular cooperative motion, which makes the azobenzene liquid crystal polymer a photoresponsive material. Liquid crystal elastomer combines the properties of polymeric elastomer with liquid crystal. It can change its shape reversibly after the application of a certain external stimulus and convert the light energy to mechanical energy. Consequently, it has many potential applications in the fields of artificial muscle and biological materials. Furthermore, as thiol-ene click reaction is compatible with water and oxygen, it is widely used in the preparation of various polymers. In this paper, we prepared azobenzene liquid crystal polymers and liquid crystal elastomers, and studied their liquid crystal phase behaviors. Meanwhile, we studied the potential application of a homemade photoresist in direct laser writing and the alignment of liquid crystal in micro-structures. The main contents are as follows:(1) Most of the polysiloxane-based liquid crystal polymers are prepared through hydrosilylation reaction. This method requires noble metal platinum, which is very expensive and difficult to be removed during the purification procedure. Furthermore, this hydrosilylation reaction usually results in a mixture of Markovnikov and anti-Markovnikov addition products, which complicate the properties of the liquid crystal polymers. In this paper, we successfully prepared two kinds of side-chain azobenzene liquid crystal polymers. Both polymers were characterized by 1HNMR, indicating this method could obtain polysiloxane-based liquid crystal polymers. Meanwhile, we studied the property of these polymers by differential scanning calorimetry(DSC), polarized optical microscope(POM) and X-ray diffraction(XRD).(2) Two-photon laser direct writing can be used to prepare complex 2D and 3D microand nanostructures. Many materials have been reported that can be applied to direct laser writing. As thiol-ene click reaction is compatible with water and oxygen, we prepared a thiol-ene based photoresist with liquid crystal polymer and successfully fabricated microand nanostructures with liquid crystal elastomer. Through dose test, we learned the threshold, resolution and feature size of the photoresist, and accordingly fabricated a variety of complex 2D and 3D liquid crystal elastomer with appropriate laser parameters.(3) Through direct laser writing, we achieved alignment of liquid crystal molecules with the help of laser. The preferred orientation of the liquid crystal molecules was studied by polarized optical microscopy and polarized infrared spectroscopy. The relationship between the order parameter and the line width and the laser energy was studied by polarized infrared spectroscopy and scanning electron microscopy. Meanwhile, we also observed the alignment of liquid crystal molecules in other structures such as a round structure and a woodpile structure, and successfully prepared a four-orientation grating. These results indicated that orientation of liquid crystal molecules could be controlled by adjusting the direction of the laser.