可见与近红外光致形变液晶高分子材料的研究

【作者】 吴伟；

【导师】 俞燕蕾；

【作者基本信息】 复旦大学 ， 材料物理与化学， 2012， 博士

【摘要】 光致形变液晶高分子材料,由于能实现光能到机械能的直接转换,近年来受到人们的广泛关注。本论文紧跟光致形变液晶高分子材料的发展趋势及其在实际应用上的需要,研究开发了全新结构的可见光与近红外光致形变液晶高分子材料。首先通过多步有机合成反应制备了新型的含反应基团的可见光响应线性液晶高分子,然后利用后交联的方法实现了大尺寸可见光致形变液晶高分子材料的制备。另外,利用稀土纳米粒子的上转换发光首次实现了液晶高分子材料的近红外光致形变。主要研究结果如下：1)全新结构的含反应基团的可见光响应线性液晶高分子的制备与性能。通过多步有机合成反应制备了可见光响应液晶单体2-甲基-4-(4”-琥珀酰亚胺酯基苯乙炔基)-4’-[11-(丙烯酰基氧基)十一烷氧基]偶氮苯(M1)和非光响应液晶单体4-己氧基苯-4’-[11-(丙烯酰基氧基)十一烷氧基]苯甲酯(M2),然后通过自由基聚合,由单体M1制备出可后交联型线性高分子PM1,由单体M1和M2共聚制备出低光响应基团含量的无规共聚物PM1M2。通过1H NMR, FTIR, GPC等对所制备的单体和高分子的结构进行了表征分析。DSC和POM分析结果表明,单体M1、M2及高分子PM1、PM1M2都具有液晶性,同时,发现PM1M2的玻璃化转变温度比PM1明显降低了约50℃,这是由于PM1M2的共聚组分M2含有较长的柔性尾基。此外,研究了高分子PM1和PM1M2在不同波长可见光照射下(405nm或445nm)的光致异构化行为,发现两种波长可见光都能诱导光响应基团发生异构化,这为由PM1和PM1M2组成的交联液晶高分子(CLCP)材料的可见光致形变提供了必要证据。2)大尺寸可见光致形变液晶高分子材料的制备及其光致形变行为研究。利用含反应基团的线性液晶高分子PM1和PM1M2,通过旋涂技术和表面涂覆技术及后交联反应,制备出大尺寸的CLCP薄膜材料。研究了所制备的CLCP薄膜材料在不同波长可见光(405nm或445nm)照射下的光致弯曲形变行为,PM1薄膜与PM1M2薄膜在405nm或445nm波长可见光的照射下都能产生快速的弯曲形变,这是由于薄膜表面的偶氮二苯乙炔单元吸收光能后发生顺反异构化,并引起液晶基元排列发生变化,使薄膜表面产生收缩引起弯曲形变。弯曲的薄膜在经过577nm波长可见光的照射后或通过加热能回复到初始的平整状态,而且该过程能够循环多次。PM1薄膜与PM1M2薄膜经过445nm波长可见光(功率为40mW)照射6秒钟后的光致应力可分别达到0.33MPa和0.26MPa。为了获得大尺寸的CLCP材料,新颖结构的线性液晶高分子PM1和PM1M2所含琥珀酰亚胺基团与己二胺在室温下发生交联反应是十分关键的。这种通过后交联制备光响应CLCP材料的方法,简单易行,不仅有利于大尺寸CLCP薄膜材料的制备,而且容易实现与其它材料(如聚乙烯等柔性膜或其它功能材料)的复合加工,大幅度提高材料的机械性能或增加材料的其它功能,推动CLCP材料在全光驱动柔性器件开发上的广泛应用。3)基于上转换发光的近红外光致形变液晶高分子材料研究。开发了一种新型的光致形变液晶高分子复合材料体系,通过将含偶氮二苯乙炔CLCP薄膜与上转换发光纳米粒子(UCNPs) NaYF4:YbTm复合,得到的CLCP/UCNPs复合薄膜在连续波980nm近红外光照射下可产生快速的弯曲形变,这是因为发光纳米材料的上转换紫外和可见发光诱导了偶氮二苯乙炔单元从反式到顺式的光致异构,以及液晶基元排列的变化。当辐射光源照射移开后,弯曲薄膜迅速地回复到初始的平整状态。而且,复合薄膜在连续波980nm波长光的持续照射下能保持弯曲变形,这是由于偶氮二苯乙炔部分的顺式-反式光异构化产生持续应力,在持续应力作用下使得复合薄膜弯曲形变能够保持。此外,在重复快速开关近红外光辐射下,复合薄膜表现出很好的弯曲和回复可逆性。值得注意的是,我们首次实现利用UCNPs作为近红外光能的传递工具完成近红外光诱导光响应变化：1)诱导偶氮二苯乙炔单元发生反式(trans)到顺式(cis)的光异构反应；2)诱导CLCP发生光化学液晶相转变；3)诱导CLCP/UCNPs复合薄膜发生光致弯曲形变。这种新颖的光致形变液晶高分子体系在生物领域具有很好的应用前景,可应用于人工肌肉执行器、全光驱动开关等。更多还原

【Abstract】 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.更多还原