A model of crack based on dislocations in smectic A liquid crystals

A plastic crack model for smectic A liquid crystals under longitudinal shear is suggested. The solution of the screw dislocation in smectic A is the key to the correct result that we obtained by overcoming a longstanding puzzle. We further use the dislocation pile-up principle and the singular integral equation method to construct the solution of the crack in the phase. From the solution, we can determine the size of the plastic zone at the crack tip and the crack tip opening （tearing） displacement, which are the parameters relevant to the local stability/instability of materials. Our results may be useful for developing soft-matter mechanics.

SYNTHESIS AND CHARACTERIZATION OF NOVEL CHIRAL SMECTIC C(Sc~*) PHASE SHISH-KEBAB TYPE LIQUID CRYSTALLINE BLOCK COPOLYMERS

A new series of chiral shish-kebab type liquid crystal block copolymers that form the smectic C(Sc*) phase was synthesized by solution polycondensation. The copolymers were characterized by GPC, DSC, TG, POM, X-ray diffraction and polarimeter. The copolymers 7 entered into liquid crystal phase whin they were heated to their melting temperatures (T-m) and the copolymers 8 were in liquid crystal phase at room temperature with low viscosities. The smectic sanded texture or focal-conic texture were observed on POM. All the chiral block copolymers showed high optical activity. No racemization has happened. Temperature-variable X-ray diffraction study together with POM and polarimetric analysis realized that they are chiral smectic C(Sc*) phase. Thus we offer in this report the first example of shish-kebab type liquid crystal block copolymers that form a chiral smectic C(Sc*) phase. The variation of melting and isotropization temperatures with molecular structure was also discussed.

Electro-optical properties and(E,F) phase diagram of fluorinated chiral smectic liquid crystals

Fluorinated smectic liquid crystals each with a biphenyl benzoate rigid core are investigated. Molecular structures of the studied compounds have difference only in fluorine position and the length of the carbon chain. Dielectric relaxation study and electro-optical measurements are carried out with the classical SSFLC geometry. The field-induced phase transitions are studied and the（E,T） phase diagram is established.

Field-induced phase transitions in chiral smectic liquid crystals studied by the constant current method

In ferroelectric liquid crystals, phase transitions can be induced by an electric field. The current constant method allows these transition to be quickly localized and thus the（E, T） phase diagram of the studied product can be obtained.In this work, we make a slight modification to the measurement principles based on this method. This modification allows the characteristic parameters of ferroelectric liquid crystal to be quantitatively measured. The use of a current square signal highlights a phenomenon of ferroelectric hysteresis with remnant polarization at null field, which points out an effect of memory in this compound.

Dielectric and Spontaneous Polarization Studies of a Ferroelectric Chiral Smectic Liquid Crystal

Dielectric relaxation and spontaneous polarization studies have been carried out in a low molar mass organosiloxane liquid crystal, TSi10PPBN4 which displays a wide temperature range of de Vries Smectic A* and chiral Smectic C* phases. The temperature variation of the permittivity and dielectric loss studied are found to have anomalous variations in the vicinity of the phase transitions. The frequency variation of permittivity and dielectric loss are also studied in the de Vries Smectic A* and Smectic C* phases. The relaxation frequency, fR is found to decrease with decreasing temperature. Temperature variation of fR is found to follow an Arrhenius shift from which the activation energy is estimated. The thermal variation of the spontaneous polarization, Ps is measured using the polarization reversal technique in the Smectic C* phase. Ps increases initially, reaches a peak value and then drops drastically in the vicinity of the SmC*-SmA*de Vries phase transition.

近晶相液晶超结构的多元外场调控

利用液晶的自组装和刺激响应特性,实现近晶相液晶多层级超结构的灵活构筑、动态操控和多功能应用对于激发更多前沿的创新性功能器件并推动液晶超结构的实用化进程具有重要意义。本文从近晶相液晶超结构的生长制备、多元外界刺激对缺陷结构的调制方法和动态调控规律等方面进行系统研究。首先,探究了图案化取向场和旋涂条件对近晶相液晶拓扑超结构的形态与大小的操控;然后,验证了焦锥畴超结构的微透镜成像功能,并通过材料复合优化和引入聚合物稳定策略,实现了正方焦锥畴阵列在35℃下(向列相)的电刺激动态调控性能;最后,研究了手性、光场和热场对双相态液晶超结构带来的多维度调控。本研究充分利用光取向场、聚合物网络、电场、手性、光场等多元外场刺激,实现了对近晶相液晶多层级超结构的多维度调控。

光控取向引导的液晶序演变

液晶独特的取向序和位置序为其带来奇特的物理性质,使其在凝聚态软物质中占据了重要的地位。由于液晶有序结构中连续对称性的破缺,引入了拓扑缺陷。而拓扑缺陷在相变过程中的转变机制及其在外场作用下的有序控制生成一直广受关注。通过控制液晶系统的空间尺度、边界条件和外场刺激,以及引入不同的热力学过程,液晶分子将呈现截然不同的组装行为,伴随各种拓扑缺陷的出现,以实现系统自由能的最小化。然而目前对液晶相变过程中拓扑缺陷的有序控制和动力学演变、外场作用下的受控转变行为和机制,以及拓扑缺陷应用探索等方面仍有待进一步研究。本文综述了本课题组利用光控取向技术实现高精度任意可编程的二维平面锚定设计,通过二维光取向层引导了液晶分子的三维排列,从而实现了不同相态下拓扑缺陷的可控有序大面积生成。进一步借助Landau-deGennes理论,揭示了拓扑缺陷在相变过程中的演化机制,并挖掘了其背后的演化规律。本研究丰富了人们对有序系统自组装行为的理解,为探索拓扑缺陷的可控生成及应用探索铺平了道路。

Local high-density distributions of phospholipids induced by the nucleation and growth of smectic liquid crystals at the interface

Amphiphilic molecules adsorbed at the interface could control the orientation of liquid crystals(LCs)while LCs in turn could influence the distributions of amphiphilic molecules.The studies on the interactions between liquid crystals and amphiphilic molecules at the interface are important for the development of molecular sensors.In this paper,we demonstrate that the development of smectic LC ordering from isotropic at the LC/water interface could induce local high-density distributions of amphiphilic phospholipids.Mixtures of liquid crystals and phospholipids in chloroform are first emulsified in water.By fluorescently labeling the phospholipids adsorbed at the interface,their distributions are visualized under fluorescent confocal microscope.Interestingly,local high-density distributions of phospholipids showing a high fluorescent intensity are observed on the surface of LC droplets.Investigations on the correlation between phospholipid density,surface tension and smectic LC ordering suggest that when domains of smectic LC layers nucleate and grow from isotropic at the LC/water interface as chloroform slowly evaporates at room temperature,phospholipids transition from liquid-expanded to liquid-condensed phases in response to the smectic ordering,which induces a higher surface tension at the interface.The results will provide an important insight into the interactions between liquid crystals and amphiphilic molecules at the interface.

ELECTROTHERMOOPTIC EFFECT OF SMECTIC A LIQUID CRYSTALS

The elec rooptic effect of a smectic A liquid crystal has been investigated by many authors. When an appropriate electric field is applied to the smectic A liquid crystal, the transparent texture is transformed to the scattering texture through the deformation

Monotropic smectic A to double layer smectic C transition of biphenyl containing liquid crystal acetylene

5-[（4＇-Heptoxy-4-biphenylyl）carbonyloxy]-1-pentyne（A-3,7） was synthesized and the phase structures and transitions were investigated by differential scanning calorimetry（DSC）,wide angle X-ray diffraction（WAXD）,polarized light microscopy（PLM） and the molecular packing in the crystal and liquid crystalline phases were simulated by molecular dynamic simulation.The results showed that the sample formed thermodynamically metastable SmA and SmC_2 phases before crystallized during cooling and the crystal phase directly transformed into isotropic phase during heating.

Surface Anchoring Stabilized High Strength Disclinations in Smectic C Phase of a Schiff-base Liquid Crystal

The observation of disclination cores of high strength S=-2, -3, -4, -5, -6, -7, -8 in a smectic C phase of Schiff-base type liquid crystal (LC) is reported. The results of polarizing optical microscope (POM), dif-ferential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) prove that the sample exhibits smectic C phase. It is suggested that the formation of the high strength disclination is mainly ascribed to the stronger anchoring of LC molecules on the substrate due to the formation of hydrogen bonds between the pendent hydroxyl of the LC molecule and the substrate.

Crystals Array via Oriented Nucleation and Growth Induced by Smectic E Mesophase of C7-T-BTBT

Long-range order crystalline thin films of organic semiconductors have attracted wide attention owing to their high charge carrier mobility.However,uncontrolled crystal nucleation and growth during the thin film drying process cause the formation of grain boundaries,thereby limiting the long-range order.Herein,we achieved the oriented nucleation and growth of organic semiconductors by off-centre spin-coating at the temperature of the smectic E(SmE)liquid crystal mesophase,and then followed by Ostwald ripening during solvent vapour annealing.The thin film of 2-(5-heptylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophne(C7-T-BTBT)blended with 40%(mass fraction)poly(methyl methacrylate)(PMMA)was prepared by off-centrespin-coating at SmE mesophase(170°C),followed by solvent vapour annealing in chloroform for 24 h(chloroform is a good solvent for C7-T-BTBT and PMMA).The C7-T-BTBT molecules grew to rod-like crystals,which were mostly arranged parallel to each other.The crystal growth was perfect and resulted in a single crystal.The average length of the crystals was approximately 87µm.Moreover,the highest charge carrier mobility is 1.62 cm^(2)·V^(−1)·s^(−1) as against that of the film prepared at 25°C(0.06 cm^(2)·V^(−1)·s^(−1)).

基于液晶功能表面的液滴输运研究

基于液晶开放表面的微流体操纵技术是一种利用微流体学原理和微加工技术,在微纳尺度上对液体进行操纵和控制的方法,对新型微流控平台的开发至关重要。本文通过注液光滑表面的理论设计,利用液晶聚合物薄膜的可控制备,开发了取向序各向异性的功能聚合物薄膜,包括向列相聚合膜和近晶相聚合膜。研究表明,与近晶相聚合膜相比,向列相聚合膜在同等条件下,为水滴提供更快的输运速度,比近晶相聚合膜约快1个数量级。近晶相聚合膜和向列相聚合膜对于水滴的输运均具有方向选择性,实现了液滴在液晶功能表面的各向异性输运,为开发基于图案化液晶功能表面的特异性微流控技术奠定了基础。

偶氮苯侧链共聚硅氧烷的合成及液晶行为的研究

以苯酚、十一烯酸、正溴己烷、对硝基苯酚和二氯亚砜为主要原料 ,通过取代、还原、重氮化和偶合等反应 ,合成了一种新的液晶单体 4 己氧基 4′ 十一烯 [1 0 ] 酰氧基偶氮苯 ,并与聚 (甲基氢硅氧烷 )通过硅氢加成生成一种新的高分子液晶 .通过1 H NMR和IR对单体和聚合物的结构进行了表征 ,并证实了聚合物的硅氢化程度近于完全 .通过DSC和热台偏光显微镜 (POM)对单体和聚合物的液晶行为进行了研究 。

新型含氧亚甲基和亚胺桥键的液晶化合物的合成及介晶性

报道一类新的、结构通式为MeO2CC6H4CH2OC6H4CH=NC6H4Y,Y=OCnH2n+1,Me,Cl,Br,NO2,H的棒状液晶化合物的合成.通过DSC和偏光显微镜对其介晶性研究发现,除Y=H外,这些化合物均具有介晶性.当Y为非烷氧基时,呈向列相液晶;当Y为较短的烷氧基时(n=1～3),液晶化合物具有向列相(N);Y为较长烷氧基时(n=4～16),液晶化合物只有近晶B相(SB)和近晶A相(SA);SA-I相变的熵变随烷氧链原子数而奇-偶变化,但与N-I相变的“奇-偶效应”相反.

新型含氟甾体类液晶的合成与相变研究

设计并合成了 3个系列的侧位氟原子取代的甾类液晶 ,其相变行为通过偏光显微镜观察和 DSC进行验证 ,可以发现氟原子的取代位置不同 ,对化合物的相变性质影响很大。

含三氟乙氧基的二苯乙炔类液晶的合成和相变研究

设计并合成了 4个系列的新型含三氟乙氧基羰基的其芳香环上含氟或不含氟原子取代的二苯乙炔类液晶化合物 ,其相变行为通过偏光显微镜和差热分析进行了测试和观察。发现目标化合物都呈现很宽的近晶 A相 ,当另一侧的碳氢链较短时 ,还有较窄的向列相存在。芳香环上引入的氟原子在有利于向列相的同时压缩了近晶相。

硅碳烷树枝状液晶的研究

A liquid crystalline carbosilane dendrimer has been synthesized in successive steps, resulting in the formation of defined, unimolecular compound. 12 AZO-meso-units were attached on its periphery and it has a three dimentional, tree-like, starburst structure.Its phase behavior was K64 Sx115 SA123N138I. Compared with its AZO-meso-unit, 4-nitro-4’- (llydroxyhexyl)-azobenzene, whose phase behavior was K122N132I, its phase range was enlarged about 64 ℃ and two more liquid crystalline phases SA Sx were found.

光致变色聚硅氧烷液晶高分子的合成及液晶行为

通过取代、还原、重氮化和偶合等反应,合成了一种新的光致变色液晶单体4-丁氧基-4′-十一烯-[10]-酰氧基偶氮苯,并与聚(甲基氢硅氧烷)通过硅氢加成生成一种新的光致变色高分子液晶。通过1H-NMR和IR对单体和聚合物的结构进行了表征,并证实了聚合物的硅氢化程度近于完全。通过DSC和热台偏光显微镜(POM)对单体和聚合物的液晶行为进行了研究,证明了都具有液晶性。

含氟三环类液晶单体的介晶性研究

利用差示扫描量热仪(DSC)、显微热分析仪和偏光显微镜(POM)对CCP和CPP两个系列液晶材料中含氟三环类液晶单体的介晶性进行了研究。结果表明,除CPP系列中的2CPPF3和4CPPF3外,其余所有化合物均有介晶性,在液晶态可观察到部分单体的近晶相和除2CPPF3和4CPPF3外所有单体的向列相的典型织构。探讨了烷基链碳原子数、环骨架结构以及氟原子取代数目对2个系列单体相变温度的影响规律。