Visible And Near-infrared Light Deformation Caused By Liquid Crystal Polymer Materials Research

Recently, much attention has been paid to photodeformable cross-linked liquid-crystalline polymers (CLCP), as CLCP can convert light energy to mechanical energy directly. According to the development trend and requirement of actual application of photodeformable CLCP, in this thesis novel visible and near infrared (NIR) light-induced deformable CLCP have been researched and developed. Firstly, linear polymer PM1and PM1M2containing both reactive group and photoresponsive group were synthesized by using multi-step organic reactions, then the preparation of large-area CLCP film based on the polymer PM1and PM1M2was performed through a post-crosslinking reaction. Besides, NIR-light-induced deformation of CLCP film was achieved by using upconversion nanophosphors. The main results are as follows:1) Preparation and properties of linear liquid crystalline polymer containing both reactive and photoresponsive group. The monomer M1and M2, polymer PM1and PM1M2were prepared through multi-step organic synthetic reactions. Their structures were characterized by1H NMR, FTIR, GPC. DSC and POM analysis demonstrate that M1, M2, PM1and PM1M2have property of liquid crystalline in a certain temperature range; besides, glass transition temperature of PM1M2significantly lowers by50℃compared with that of PM1, owning to the influence of a long flexible tail of the M2components in PM1M2. In addition, the photoisomerization behaviors of PM1and PM1M2were investigated when irradiated with different wavelength visible light (405nm or445nm), it was found that the photoisomerization of PM1and PM1M2was able to be induced by visible light both at405nm and445nm, but the efficiency of photoisomerization induced by irradiation with visible light at405nm was higher than that at445nm.2) Preparation of photodeformable behavior of large-area CLCP films. Based on linear polymer PM1and PM1M2with reactive group, large-area CLCP films were prepared conveniently via utilizing spin-coating or casting technology followed by a post-crosslinking reaction. The resulted CLCP films (PM1film and PM1M2film) generated directional bending when irradiated with linearly polarized light at445nm or405nm by varying the polarization direction. The bent film reverted to initial flat state when irradiated with above570nm light or heating at80℃. Photoinduced stress of PM1film and PM1M2film upon irradiation with visible light at445nm (40mW) is up to0.33MPa and0.26MPa, respectively. It is noted that above-mentioned method to prepare CLCP films is simple and practicable, which is beneficial to preparation of the large-size CLCP films. Using this method, it is easy to improve mechanical property of CLCP or render other functional properties to CLCP by combining it with other materials (such as PE and other flexible film, or other functional materials), which promote a wide range of application of CLCP in development of all-optical-driven flexible devices.3) Near-infrared light induced bending of crosslinked liquid-crystalline polymer films using upcoversion nanophosphors. To develop the applications of light-driven organic actuators in the future biological systems, lower energy light, such as near-infrared (NIR) light which penetrates deeper into tissues and has less damage to biosamples, should be a more suitable stimulating source instead of UV and visible light. Therefore, upconversion nanophosphors (UCNPs) as antennae species that absorb NIR light and transfer the available energy to the photochromic units were combined into the azotolane-containing CLCP films. The resulted composite film generated fast bending upon exposure to continuous-wave near-IR light at980nm. This occurs because the upconversion luminescence of the nanophosphors leads to trans-cis photoisomerization of the azotolane units and an alignment change of the mesogens. The bent film completely reverted to the initial flat state after the light source was removed.It is the first time to report the direct actuation of the photoresponsive CLCP by NIR light. It is noteworthy that not only the photoisomerization of the chromosphores but also the alignment change of the LC mesogens can be triggered by the judicial choice of photochromic units in CLCP and UCNPs. This kind of novel photodeformable CLCP system is promising for biological applications such as artificial muscle-like actuators and all-optical switches.