【作者】 肖素芳；

【导师】 路庆华；

【作者基本信息】 上海交通大学 ， 高分子化学与物理， 2009， 博士

【摘要】 光敏聚合物由于在智能响应系统及光学器件中的潜在应用,受到了广泛关注。目前,已经开发了多种光敏材料包括染料掺杂聚合物和各种共价合成的光敏高分子。然而,掺杂聚合物由于相容性问题通常染料掺杂量不高,并且光诱导取向的稳定性差;共价合成的光敏材料光学性能优良但合成过程繁琐复杂,需多步反应,最终产率很低。因此设计合成性能优良的光敏聚合物以满足不同的应用需要,仍是目前重要的研究目标。离子自组装主要利用库仑作用将相反电荷的构筑单元结合在一起,可以根据实际应用需要,选择不同的构筑单元,精确组合复合物的结构,因此离子自组装技术为开发具有独特光物理化学性能的光敏材料提供了非常好的解决方案。本论文利用离子自组装技术探索合成了一系列的光敏超分子材料,详细研究其相态行为、光学性质及对小分子液晶取向的有效性,为新型高性能光敏材料的设计合成提供了新思路。首先基于离子自组装技术设计合成了可作为液晶取向层的光敏材料。该复合物材料通过离子偶合聚离子液体和光敏单元甲基橙制得,用傅立叶变换红外、核磁共振、热分析、正交偏光显微镜、X射线衍射、小角X射线散射和双折射等分析手段对光敏复合物材料的结构、相行为和光响应性能进行了详细研究,证实了复合物材料具有高度有序的层状纳米有序结构和较高的光敏特性。利用脉冲紫外激光辐照复合物膜,在较低能量下,可得到光学各向异性表面,取向方向垂直于激光的偏振方向;在较高辐照能量下,得到规则的周期性沟槽结构,沟槽方向平行于激光的偏振方向。液晶盒于正交偏振片间的透光率曲线和偏光显微镜观察证明,不论分子链取向的光学各向异性表面还是具有沟槽结构的形貌各向异性表面都可实现对小分子液晶的均匀取向。虽然上述光敏超分子可用于各向异性表面的制备,并实现了对小分子液晶的取向,但刚性的分子结构使聚合物膜的机械性能较差,并且限制了光诱导各向异性取向性能,因此我们进一步设计合成了一系列具有不同烷基链长度的功能组装单元偶氮离子液晶(azo-ILC),偶氮苯基团和季铵离子端间的亚甲基间隔数分别有4、6或12。通过离子自组装聚丙烯酸和偶氮离子液晶,构筑了相态可调、取向性能优良的偶氮热致液晶超分子材料(根据亚甲基间隔数的不同分别指名为PAZO4,PAZO6和PAZO12)。结果证实,该超分子材料呈现不同d间距的层状纳米有序结构。通过偏振紫外和偏振傅立叶变换红外对组装超分子材料的光取向性能进行了研究。在脉冲激光辐照下,可以获得非常突出的光学各向异性,取向方向垂直于激光偏振方向。通过激光辐照和退火处理,PAZO12的最大面内取向度的数值可达0.93,这是目前文献报道的偶氮聚合物光取向的最大值。并且发现最大面内取向度随着光敏材料清亮点温度的提高而增大,此结果可为有效光诱导取向材料的设计提供指导。由离子自组装聚电解质和商业化的表面活性剂或精心设计的双亲性功能小分子构筑的超分子材料都是单功能性的,而实际应用中往往对功能材料的要求是多方面的,因此双功能化甚至多功能化,是功能材料发展的必然趋势。为此我们提出了双功能性超分子的概念,利用离子自组装技术将光学各向异性和可调的润湿性结合起来。不同比例的光敏单元MO和全氟十二酸(FDA)作为功能侧链通离子自组装接枝到聚离子液体主链上,制备了系列双功能复合物。通过改变MO和FDA的组装比例可以实现对复合物材料表面润湿性能和光诱导各向异性的调控。488 nm偏振激光室温下辐照,可获得双折射值Δn~10-2的光学各向异性取向,并且该复合物材料光取向稳定性好。复合物膜的表面接触角随着FDA含量的增加而增大,即通过调节氟链的含量可实现表面润湿性的连续变化。更重要的是,通过调节光辐照取向的复合物取向层中FDA的比例,可以实现对液晶小分子从平面取向到垂直取向的转变。肉桂酸类聚合物及其衍生物在可见区域是无色透明的,因此在光学器件特别是液晶取向中比偶氮材料更有优势。其光化学反应包括[2+2]的光交联反应和肉桂酸的光异构化,在线性偏振光辐照下,发生光学各向异性取向的同时形成了立体交联网络,因此取向膜的稳定性好。目前,肉桂酸类光敏聚合物的非共价合成还没有报道。为此,我们通过离子自组装技术将聚乙烯苯磺酸与季铵端基的肉桂酸甲酯结合在一起,制备了肉桂酸酯侧链超分子聚合物。根据烷基链间隔长度的不同,6或12个亚甲基单元分别指名为PCAM6和PCAM12。研究了激光辐照下复合物材料的光交联性能和光诱导取向行为。将旋涂膜置于掩模板下,通过激光辐照和显影可以得到清晰的图形结构。取向研究发现,较长的柔性间隔有利于肉桂基团的光异构化,从而PCAM12的光诱导取向较PCAM6的大。另外在该交联性光学各向异性膜上实现了稳定均匀的液晶取向。更多还原

【Abstract】 Photosensitive polymers have attracted great interest in recent years due to their high potential application in smart response system and optical elements. Presently, various photosensitive materials have been exploited by doping dyes in polymers or covalent synthesis of photosensitive polymers. However, doping films usually have low dye loading and present unstable photoinduced property. Covalent photosensitive materials show better photoinduction stability, nevertheless the synthetic processes usually were rigorous and fussy and involved many steps with low yield. So the design of photosensitive polymer with optimizing properties to satisfy different applications is still the most attractive target. Ionic self-assembly (ISA) mainly employs the coulombic interaction to bind the oppositely charged tectonic units together and the complex architectures can be precisely tailored by selection of constituents according to the desire of different applications, which presents a promising situation for design of photosensitive materials with unique photochemical and photophysical properties. This dissertation describes research that is done aimed to obtain a series of photosensitive materials with improved and tunable properties by ISA technology. Their phase behavior, optical property and utility for LC alignment were investigated in detail. These preliminary studies may put more insight to the synthsis of photosensitive polymer with preferable properties.A new strategy based on ISA technology was provided for design of photosensitive material as liquid crystals (LC) alignment layer. The complex material was constructed by the coupling of poly(ionic liquid) and photosensitive unit methyl orange (MO). The structure, phase behavior and photoresponse were examined by a variety of techniques including FTIR, NMR, thermal analysis, polarized optical microscopy, X-ray diffraction, small-angle X-ray scattering and birefringence measurements. Highly ordered lamellar nanostructure and photosensitive character were confirmed. Under the irradiation of pulsed UV laser, the moderate optical anisotropic surface with the preferred direction perpendicular to the pulsed polarization or regular periodic grooves microstructure surface parallel to the pulsed polarization depend on laser fluence was obtained. The anisotropic surface of oriented molecular chain or topography was demonstrated to be resultful for the alignment of LC by the optical transmittance plot and polarizing microscopy images of LC cells with different rotation angle.Although the above photosensitive supramoleculethe prove to be useful in fabrication of anisotropic surface and subsequent LC alignment, its rigid structure results in poor mechanical property and also restricts photo-orientation. So we further elaborately design a series functional unit azobenzene ionic liquid crystal (azo-ILC) with a spacer length of 4, 6 or 12 methylene units, respectively, aim to obtain azobenzene thermotropic liquid crystalline polymer (LCP) for tunable phase behavior and improved optical orientation. The thermotropic LCP was fabricated by ISA of PAA and azo-ILC. Highly ordered liquid-crystalline structure with a lamellar morphology of different d-spacing was observed. The photo-induced orientation of azobenzene groups in thin films of the obtained ionic-bonding supramolecules was studied by polarized UV–Vis and FTIR. Under the irradiation of pulsed laser, very effective induction of optical anisotropy with the preferred direction perpendicular to the pulsed polarization was observed. Typically, the maximum in-plane orientation order of 0.93 for PAZO12 was achieved after irradiation and subsequent anneal, which was the reported crown valve up to now. It was found that the maximum S can be increased by increasing the clearing temperature of the photosensitive material. These results may provide guidelines for the design of effective photo-induced anisotropic materials. Supramolecular materials from ISA of polyelectrolyte and surfactant or elaborate amphiphilic molecules are mono-functional, while practical applications usually request material having multidimensional properties or functions. The design of difunctional and even multifunctional materials is becoming a trend of material development. Thus we proposed a concept of dual-functionalized supramolecules for effective optical anisotropy and tunable wettability. These complexes were fabricated by ISA technique that involved grafting different proportions of the photoresponsive units of MO and perfluorinated dodecanoic acid (FDA), as functional side-chains, onto a poly(ionic liquid). Surface wettability and photoinduced anisotropy could be tuned by changing of the molar ratio of MO and FDA. A pronounced anisotropic orientation with a birefringence valueΔn~10-2 was achieved at room temperature, and the complex films were found to possess the characteristics of long-term optical storage. Continuous tunable wetting properties were demonstrated and contact angles of the test liquids increased with an increase in the FDA content. Furthermore, LC orientational transition from planar to homeotropic alignment was achieved by adjusting the FDA content in the orientated complex alignment layers.Polymeric films composed of cinnamate derivatives are transparent in a visible region should be more attractive for optical devices and LC alignment. The photoreaction of cinnamate polymer includes a [2+2] photocross-linking reaction and photoisomerization of the cinnamic acid. The photocross linking make the film insluable and the photoinduced orientation very stable. In addition, it can be used to fabricate the photolithographic images for electronics applications. Herein, a kind of photosensitive polymer with photo-cross-linkable side chain group was devoloped based on ISA technology. The photo-cross-linkable supramolecules were constructed by the coupling of polyelectrolyte and cinnamate units with different spacer length (6 or 12 methylene units designated PCAM6 and PCAM12, respectively). Photochemical properties including photo-cross-linking and photoinduced orientation of complex materials were investigated by irradiating with a polarized laser. A clear photolithographic image was obtained by laser exposure. Its photoorientation result proved that long spacer length favors the photo-isomerization of the cinnamate group, which leads to higher photoinduced anisotropy for PCAM12 than that of PCAM6. Furthermore, a homogeneous and stable liquid crystals alignment was achieved on the resultant anisotropic orientation film.更多还原