【作者】 包瑞；

【导师】 唐和清； 刘承美；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2010， 博士

【摘要】 自环三磷腈液晶被发现以来,绝大部分研究工作集中在以偶氮苯、联苯等为刚性基团时的末端烷基链长度对其液晶性的影响方面。六氯环三磷腈中P-Cl键具有高的反应活性,有利于在磷腈环上引入新型功能性基团作为液晶刚性基团以及赋予环三磷腈衍生物相应的功能性。有机光电领域特别是液晶领域的快速发展,为环三磷腈衍生物液晶尤其是盘状液晶的应用提供了良好的契机。本文合成了一系列具有不同长度末端烷基取代基的腈基二苯乙烯基取代环三磷腈衍生物,探讨了烷基链长度、腈基取代位置、烷基链数目及端基取代基种类对环三磷腈衍生物液晶性的影响。通过1H,13C,31P-NMR表征了化合物分子结构,并使用元素分析确定了化合物的纯度。通过差式扫描量热(DSC)和偏光显微镜(POM)研究了环三磷腈衍生物的液晶性。结果表明,所有具有1个末端取代基的腈基二苯乙烯基取代环三磷腈衍生物均表现出向列相液晶态,而具有2个末端取代基的腈基二苯乙烯基取代环三磷腈衍生物则表现出柱状液晶态。显然,端基取代基数目对环三磷腈衍生物的分子构型有极大的影响,连有单取代基的环三磷腈倾向于形成取代基3上3下的棒状分子构型,而连有双取代烷基链的环三磷腈倾向于形成取代基向侧面铺展的盘状分子构型；随着末端烷基链长度的增加,环三磷腈衍生物的清亮点温度逐渐升高；腈基取代位置不同的环三磷腈衍生物表现出不同的相转变焓变值；末端取代基对环三磷腈衍生物的液晶性有显著的影响：没有端基取代基的化合物未能表现出液晶态,而具有端基取代基的化合物均能表现出单向或双向向列相液晶态,说明了端基取代基是环三磷腈衍生物表现出液晶态的基本条件之一。此外,柔性烷基链数目的增多增加了环三磷腈化合物分子的柔性,降低了清亮点温度。末端烷基双取代化合物具有比单取代化合物更低的清亮点温度。同时,柔性烷基链数目的增多也有利于在降温中保持液晶态织构。通过加热-冷却操作制备了环三磷腈衍生物的有机凝胶,研究了凝胶性质及烷基链长度对荧光增强现象的影响。结果表明所研究的环三磷腈衍生物在单一有机溶剂中不能够形成稳定的凝胶,而在四氢呋喃／甲醇等混合溶剂中可以形成稳定的有机凝胶。经冷冻干燥后的凝胶的形貌为纤维网状。环三磷腈衍生物在四氢呋喃／水混合液中可以表现出明显的荧光增强现象,随着末端烷基链长度的增加,化合物表现出的荧光增强比例逐渐增大,其在80%水含量的四氢呋喃／水溶液中形成的纳米颗粒的直径也逐渐减小。较小的颗粒直径和较大的颗粒含量有利于产生更强的荧光发射。此外,聚合物稳定胆甾相织构(PSCT)光阀在使用过程中的能耗问题一直限制着其发展,需要开发新型低能耗PSCT光阀以满足其逐步增大的市场需求。为了降低PSCT液晶光阀在使用过程中的能耗,通过调整聚合物浓度,制备了双稳态PSCT光阀,并研究了其热稳定性。结果表明含有高聚合物浓度的液晶光阀表现出相对最好的热稳定性。具有5.10%单体浓度的PSCT光阀在温度高于41℃时呈现散射态,温度降低后只需施加短的电压脉冲便可将光阀恢复透明态,这种热写入电擦除式的液晶光阀可以应用于高楼外墙的智能窗。在水平和垂直两种模式液晶盒中研究了液晶单体4-腈基苯基-4’-(6-丙烯酸己酯氧基)苯甲酸酯(RM23)的光聚合行为。结果表明在3%单体浓度下,液晶聚合物具有较小的分子量分布指数(PDI)。聚合物的PDI和分子量随着单体浓度的增加而逐渐增大。在水平模式液晶盒中,光聚合后的混合物表现出均匀的暗红色织构。在垂直模式液晶盒中,光聚合后的混合物随着聚合物浓度的增大,向列相液晶织构逐渐消失。更多还原

【Abstract】 Since the first report about cyclotriphosphazene-based liquid crystal, the main work in this field was focusing on the effect of the length of terminal alkyl chain on the liquid crystalline properties of cyclotriphosphazenes with azobenzene or biphenyl rigid groups. The high reactivity of P-Cl bond in hexachlorocyclotriphosphazene facilitates the introduction of novel functional group on the phosphazene ring. Therefore, the introduced functional group not only could act as a rigid group but also could functionalize the corresponding cyclotriphosphazene derivative. More opportunities for the application of cyclotriphosphazene-based liquid crystal, especially the disk-like liquid crystal are anticipated due to the rapid development of organophotonics and liquid crystals.In this thesis, a series of cyanostilbene-containing cyclotriphosphazene derivatives with different lengths of terminal alkyl chains were synthesized. The effects of the length of alkyl chain, cyano-substituted position, the number of terminal alkyl chain and different kinds of terminal group on the liquid crystalline properties of the cyclotriphosphazene derivatives were studied. The molecular structures and purity of the products were characterized by 1H,13C,31P-NMR and elemental analysis. The liquid crystalline properties of cyclotriphosphazene derivatives were studied by the means of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM).It was found that all the compounds with one terminal substituent exhibited nematic phases, and all the compounds with two terminal alkyl chains exhibited columnar phases. The number of the terminal substituent has great effect on the alignment of the cyclotriphosphazene molecule. Mesogenic units that contain only one terminal group give rise to calamitic alignment with three arms pointing upward and three other arms pointing downward. On the other hand, mesogenic units that contain two terminal alkyl chains give rise to disk-like alignment. As the length of the terminal alkyl chain was increased, the clear temperatures of cyclotriphosphazene-based liquid crystals increased. The cyclotriphosphazene derivatives with different substituted position of the cyano group exhibited different enthalpies of phase transition. The terminal subtituent has obvious effect on the liquid crystalline properties of cyclotriphosphazene derivatives. Compound without terminal substituent didn’t exhibit liquid crystalline properties both on heating and cooling run. Compounds with different terminal substituents exhibited monotropic or enantiotropic nematic phases. The results mean that the terminal substituent is essential to the formation of liquid crystallinity in cyclotriphosphazene derivatives. Moreover, the rigidity of the cyclotriphosphazene molecule was reduced with increasing number of soft alkyl chains, therefore, the clear temperature of the cyclotriphosphazene-based liquid crystal was also reduced. Compounds with relatively large number of alkyl chains exhibited lower clear temperatures than those of compounds with one terminal alkyl chain. At the same time, the increase of number of terminal alkyl chains facilitated holding the liquid crystalline textures on cooling.The organogels formed by cyclotriphosphazene derivatives were prepared through heating-cooling method. The gelation properties and effect of length of alkyl chain on the fluorescent enhanced emission phenomenon were studied. It was found that cyclotriphosphazene derivatives could form stable organogels in THF/methanol mixed solvents, but could not form stable gels in single solvents. Fibrous aggregates were observed in the dried gels of cyclotriphosphazene derivatives. All the studied compounds could exhibit the aggregation-induced enhanced emission (AIEE) phenomenon in diluted THF/water mixed solution due to the formation of nanoparticles’ suspension. Compounds with increasing length of terminal alkyl chains showed increasing fluorescence intensities in the nanoparticles’ suspension. The size of nanoparticles (H2O/THF=4/1, v/v) decreased with increasing length of terminal alkyl chains. Small size of nanoparticle and large content of nanoparticle in nanoparticles’suspension facilitated the strong fluorescent emission.The development of polymer stabilized cholesteric texture (PSCT) light shutter is limited by its high energy consumption, novel PSCT light shutter with low energy consumption is required to meet the requirement of developing market. In order to reduce the energy used to stabilize the PSCT light shutter, bistable PSCT light shutters were developed by increasing the polymer concentration. The thermal properties of the PSCT light shutters were studied. It was found that the liquid crystal light shutter with the relatively highest polymer concentration exhibited the best thermal stability. The light shutter with 5.10% of monomer concentration was switched to scattering state when the temperature was higher than 41℃. The scattering state was switched to transparent state when the light shutter was applied a short voltage pulse. This thermally written and electrically erased light shutter could be used as smart windows in high buildings.The photo-polymerization of liquid crystalline monomer 4-cyanophenyl-4’-(6-acryloyloxyhexyloxy)benzoate (RM23) was studied both in reverse and normal mode liquid crystal cells. The results indicated that the low PDI was obtained in the reverse and normal modes at the monomer concentration of 3%. The PDI and molecular weight increased with monomer concentration. In the reverse mode cells, uniform dark red textures were observed after photo-polymerization. In the normal mode cells, textures attributed to the nematic phase disappered gradually with monomer concentration.更多还原