Phenomenological theory of textured mesophase polymers in weak flows

A macroscopic viscoelastic model for incompressible, isothermal, homogeneous lyotropic mesophases exhibiting the nematic polydomain texture is presented. Under equilibrium static conditions the model describes a three dimensional tessellation, where each region or nematic domain has a characteristic size and orientation, and where the polydomain texture has a random orientation. Close form expressions that define the characteristic texture size and the number of randomly oriented domains are given. When subjecting the model lyotropic liquid crystalline polymer displaying the polydomain texture to a steady rectilinear shear flow, the predicted characteristic texture size decreases with increasing shear rates. The power law scaling relations of texture size with shear rate are in excellent agreement with the experimental measurements. The steady shear flow orientation predictions, characterized by a positive shear dependent alignment angle and a low orientation, are in agreement with experimental data.     

手征性侧链液晶高分子取向结构的研究

用偏光显微镜,红外二色性和Ｘ 射线衍射研究了一种手征性侧链液晶高分子的相态织构和弛豫行为．偏光显微镜观察这种侧链液晶高分子冻结取向液晶态薄膜时,可观察到与剪切方向垂直的明暗相间的条带织构．红外二向色性的结果表明,取向态中侧链上的介晶基元倾向于与剪切方向垂直排列．取向和非取向膜的Ｘ射线衍射揭示了该侧链液晶高分子具有反铁电性液晶的两套反相螺旋结构．取向薄膜在液晶态的弛豫行为表明,取向作用能促进侧链高分子近晶相层状结构的生长,而且介晶基元的取向在弛豫过程中能保持下来．     

Anisotropic cellulose-derived matrix for dispersed liquid crystals

New cellulose-derived dispersed liquid crystal free-standing thin films were prepared by a shear-casting technique from anisotropic and isotropic solutions of thermotropic (acetoxypropyl)cellulose in N,N-dimethylacetamide with different amounts of the nematic E7. For films prepared from anisotropic solutions, dispersed nematic E7 droplets of micron and submicron size were found to coexist, with the band texture characteristic of polymer liquid crystals after shearing. Mechanical properties including Young's modulus and stress-strain curves were determined along and perpendicular to the shear direction, and revealed the anisotropic behaviour of films prepared from lyotropic solutions. The nematic E7 component appears to promote chain mobility and rearrangement of the polymer matrix and to modify the viscoelastic properties of the matrix.     

尼龙1010对乙基氰乙基纤维素液晶态的影响

在尼龙1010/乙基氰乙基纤维素/二氯乙酸体系中,尼龙1010/二氯乙酸溶液相与乙基氰乙基纤维素/二氯乙酸溶液相不相容,各自形成相区。在乙基氰乙基纤维索含量一定时,增加尼龙1010的量,使液晶相转变温度提高,液晶相的织构也由于乙基氰乙基纤维素/二氯乙酸溶液相的浓度的增大而发生变化。在受到切应力作用后,液晶溶液形成条带织构,条带的方向与应力方向垂直。随着取向的大分子链的松驰解取向,各条带中沿着大分子链取向的方向上出现许多暗带线.把条带分剖成约0.5-1.0μm长的小块。在足够长的时间后,在切应力的方向上形成许多较宽的带。这些带由许多基本相互平行并与宽带形成一角度的小细带组成。上述现象除了与取向大分子链的松弛有关外,可能还与尼龙1010/二氯乙酸溶液相和乙基氰乙基纤维素/二氯乙酸溶液相的相分离有关。     

UV-initiated solidification of liquid crystalline ethylcellulose/acrylic acid films and bands formed in this process

Solidification of liquid crystalline ethylcellulose/acrylic acid films was realized by UV-initiated polymerization of the solvent acrylic acid. It has been found that the original textures were immobilized to a great extent, and a novel “banded texture” formed at the same time. The optical properties of this texture were different from the banded texture formed by shearing lyotropic or thermotropic polymer liquid crystals. Formation of such bands is assumed to be related to an uncompleted phase separation.     

乙基醋酸纤维素液晶态条带织构的形成机理

本文应用平行板移动式和转动式二种剪切装置研究了乙基醋酸纤维素的二氯乙酸体系液晶态受剪过程形成条带织构的临界剪切速率,条带织构的形成机理以及所形成的条带织构在升降温过程中的变化。结果表明,高分子液晶态受剪过程条带织构不是在受剪时产生,而是在受剪停止后的弛豫过程中形成的。可以观察到条带织构出现的诱导时间(t_b),其值的大小与溶液的浓度、剪切速率等因素有关。最后提出一模型来解释高分子液晶态受剪切过程条带织构的形成机理。     

Properties of a liquid crystalline polyester with a mesogen containing the bicyclooctylene ring

A liquid crystalline polyester with a decamethyene flexible spacer and a mesogenic unit containing a central 1,4-bicyclo(2,2,2)octylene ring was prepared for comparison with the equivalent polymer containing a central p-phenylene ring in the mesogen. Both polymers formed a nematic phase on melting, and as expected, the former had a much lower isotropization temperature than the latter. The polymer containing the bicyclooctylene ring, however, showed a batonnet texture, indicative of a smectic phase, at a temperature above that of the nematic state, especially on cooling from the isotropic melt.     

Direct observation of director fields of disclinations in the nematic mesophase of a main chain thermotropic aromatic polyester by surface microcrack decoration

For a main chain thermotropic aromatic polyester with a flexible spacer, Cr 194 N 245 I (°C), the director fields around disclinations in the nematic mesophase can be decorated by both the solidification-induced band texture and surface microcracks. Director fields of various types of disclinations, including inversion walls, in the nematic mesophase of this semi-rigid polyester have been observed directly by polarizing optical microscopy. It was found that when the polymer was pre-sheared in the nematic state and then quenched to room temperature, a shear-induced band texture was observed, which relaxed slowly during annealing at 200°C, and then on quenching the solidification-induced band texture and surface microcracks appeared, displaying the pattern of the disclination fields. Pre-shearing is a necessary condition for the appearance of microcracks. On annealing, disclinations of various types were generated, quite often connected by inversion walls in the direction of pre-shearing. In some areas of the specimen where the shear-induced bands had not been completely relaxed during annealing, the shear-induced band texture was shown by the birefringence and surface microcracks to have a supermolecular structure of sinusoidal chain fibrils.     

Direct observation of director fields of disclinations in the nematic mesophase of a main chain thermotropic aromatic polyester by surface microcrack decoration

For a main chain thermotropic aromatic polyester with a flexible spacer, Cr 194 N 245 I (°C), the director fields around disclinations in the nematic mesophase can be decorated by both the solidification-induced band texture and surface microcracks. Director fields of various types of disclinations, including inversion walls, in the nematic mesophase of this semi-rigid polyester have been observed directly by polarizing optical microscopy. It was found that when the polymer was pre-sheared in the nematic state and then quenched to room temperature, a shear-induced band texture was observed, which relaxed slowly during annealing at 200°C, and then on quenching the solidification-induced band texture and surface microcracks appeared, displaying the pattern of the disclination fields. Pre-shearing is a necessary condition for the appearance of microcracks. On annealing, disclinations of various types were generated, quite often connected by inversion walls in the direction of pre-shearing. In some areas of the specimen where the shear-induced bands had not been completely relaxed during annealing, the shear-induced band texture was shown by the birefringence and surface microcracks to have a supermolecular structure of sinusoidal chain fibrils.     

Self-alignment of dye molecules in micelles and lamellae for three-dimensional imaging of lyotropic liquid crystals

We report alignment of anisotropic amphiphilic dye molecules within oblate and prolate anisotropic micelles and lamellae, the basic building blocks of surfactant-based lyotropic liquid crystals. Absorption and fluorescence transition dipole moments of these dye molecules orient either parallel or orthogonal to the liquid crystal director. This alignment enables three-dimensional visualization of director structures and defects in different lyotropic mesophases by means of fluorescence confocal polarizing microscopy and two-photon excitation fluorescence polarizing microscopy. The studied structures include nematic tactoids, Schlieren texture with disclinations in the calamitic nematic phase, oily streaks in the lamellar phase, developable domains in the columnar hexagonal phase, and various types of line defects in the discotic cholesteric phase. Orientational three-dimensional imaging of structures in the lyotropic cholesterics reveals large Burgers vector dislocations in cholesteric layering with singular disclinations in the dislocation cores that are not common for their thermotropic counterparts.     

Morphology of polymer networks polymerized in highly ordered liquid crystalline phases

The morphology and optical properties of polymer stabilized liquid crystals formed in a more highly ordered low molecular weight liquid crystal solvent were studied. Tetrafunctional, mesogenic monomers (with and without flexible spacers) were polymerized in isotropic, nematic and smectic phases of the LC solvent (4′-octyl-4-cyanobiphenyl) and studied with scanning electron microscopy and cross-polarized light microscopy. The network morphology of the nematic and isotropic phase polymerizations showed strong similarities with the corresponding polymerizations in other solvents. Polymerization in the smectic phase, however, resulted in marked increases in network order and directionality. Most dramatically, even the polymer without flexible spacer formed a fibrous network of rodlike units, in contrast to the random, beaded texture formed by the same polymer in nematic or isotropic conditions. Correspondingly, a large increase in birefringence demonstrated significant polymer orientation and more effective orientational interaction with the liquid crystalline solvent.     

Rheology of a lyotropic mesophase through a stress-relaxation experiment

We report on the first rheological study of the structural relaxations in a nematic liquid crystalline phase. Linear dynamic and transient shear experiments were applied to a polydomain nematic phase of the CTAB/water system: a liquid crystalline mixture composed of 28 wt% CTAB at 35 degrees C. The decay of the shear modulus, G(t), was analyzed using the CONTIN inverse Laplace transform to obtain a distribution of relaxation times which were compared with ones from the usual fitting procedure based on a generalized Maxwell model. The behavior of the nematic lyotropic structure of the CTAB/water system is characterized by the presence of both slow and fast relaxation times. These were interpreted as being due to a progressive loss of the lyotropic domain orientation and to the breaking/reforming process of the cylindrical aggregates, respectively.     

Monte Carlo simulation of the self-assembly and phase behavior of semiflexible equilibrium polymers

Grand canonical Monte Carlo simulations of a simple model semiflexible equilibrium polymer system, consisting of hard sphere monomers reversibly self-assembling into chains of arbitrary length, have been performed using a novel sampling method to add or remove multiple monomers during a single MC move. Systems with two different persistence lengths and a range of bond association constants have been studied. We find first-order lyotropic phase transitions between isotropic and nematic phases near the concentrations predicted by a statistical thermodynamic theory, but with significantly narrower coexistence regions. A possible contribution to the discrepancy between theory and simulation is that the length distribution of chains in the nematic phase is bi-exponential, differing from the simple exponential distribution found in the isotropic phase and predicted from a mean-field treatment of the nematic. The additional short length-scale characterizing the distribution appears to arise from the lower orientational order of short chains. The dependence of this length-scale on chemical potential, bond association constant, and total monomer concentration has been examined.     

The cellular optical texture of the lyotropic nematic phase of the caesium pentadecafluoro-octanoate(CsPFO)/water system in cylindrical tubes

The nematic phase of the CsPFO/water system, when held in a cylindrical glass tube, spontaneously forms a detailed 'cellular' texture with an axial S = +1 disclination. This texture is the lyotropic discotic analogue of that previously found for a calamitic thermotropic system.     

溶致性液晶高分子PBT的结构表征

聚苯撑苯并二噻唑(PBT)具有典型的溶致性液晶行为,聚合后期有液晶态搅拌乳光现象。偏光显微镜观察到具有向列型织态结构,溶液粘度随浓度变化,当进入液晶区时有明显的反常突变。对高分子链和凝聚态结构进行了X射线衍射研究,测定了晶胞参数、C轴等同周期和高分子链的取向度,并表明取向的PBT凝聚态是由刚性棒状的分子呈园柱体形态二维有序堆砌而成的。     

Direct decoration of disclinations by solidification-induced band texture and focal-conic texture for a low molar mass liquid crystal

Two decoration methods, solidification-induced band texture decoration and focal-conic texture decoration, were established to map the director field of disclinations in a low molar mass methacrylate liquid crystal. It was found that when the specimen film is quenched from the nematic melt to room temperature, solidification-induced band texture is observed arrayed along with the schlieren texture, and the orientation of the director field can be displayed. Moreover, when the specimen is cooled from the nematic melt to 63°C and annealed, the focal-conic texture of the smectic A phase is found to grow around the corresponding disclination core with good orientation to reveal the director field. By the two decoration techniques, the director fields of disclinations with strength s = 1/2 and s = ±1 were revealed. Two types of inversion wall, loop-like wall and splay-type wall, were found by both solidification-induced band texture decoration and focal-conic texture decoration.     

分级聚丙烯的取向结晶过程

聚丙烯熔体在剪切或应变应力作用下 ,分子链发生取向形成伸直链纤维晶 ,这些先取向形成的纤维晶成为其后结晶的晶核 .这种线形排列的特殊自晶核被称作排核 ( Row nuclei) [1] .排核诱导的结晶温度高于异相核和均相核 .折叠链片晶在排核上附生生长 ,形成具有柱状对称性的超分子结构 ,称为柱状晶 ( Cylindrite) [2 ,3] .聚合物的分子量 ,剪切温度和剪切速度等因素对柱状晶的生成有很大影响 [4 ,5] .本文选用不同级分的聚丙烯样品 ,利用高分子 (特别是取向结晶 )的记忆效应 [6,7] ,研究了剪切后薄膜试样在熔融重结晶过程中柱状晶的形成和发展…     

Aqueous cholesteric liquid crystals using uncharged rodlike polypeptides

The aqueous, lyotropic liquid-crystalline phase behavior of the alpha-helical polypeptide, poly(N(epsilon)-2-[2-(2-methoxyethoxy)ethoxy]acetyl-lysine) (1), has been studied using optical microscopy and X-ray scattering. Solutions of optically pure 1 were found to form cholesteric liquid crystals at volume fractions that decreased with increasing average chain length. At very high volume fractions, the formation of a hexagonal mesophase was observed. The pitch of the cholesteric phase could be varied by a mixture of enantiomeric samples L-1 and D-1, where the pitch increased as the mixture approached equimolar. The cholesteric phases could be untwisted, using either magnetic field or shear flow, into nematic phases, which relaxed into cholesterics upon removal of field or shear. We have found that the phase diagram of 1 in aqueous solution parallels that of poly(gamma-benzyl glutamate) in organic solvents, thus providing a useful system for liquid-crystal applications requiring water as solvent.     

Synthesis and lyotropic liquid crystal properties of chiral helical polycarbodiimides

Chiral helical polymers have been expected to exhibit optical activity with a significantly large optical rotation power. In this paper polymethylphenylethylcarbodiimides (Poly-PhEMCDI) with helical structure were synthesized by the insertion polymerization of a corresponding chiral monomeric carbodiimide initiated by a copper complex. The circular dichroism spectra and optical rotation power induced by the ordered rigid main chain helical structure of polycarbodiimides, in solution and as cast films, were studied. Polycarbodiimides have a rigid rod helical structure and form lyotropic liquid crystal (LLC) in organic solvents such as dichloromethane (DCM), chloroform and THF. The LLC phase was studied using polarizing optical microscopy and X-ray diffraction. A chiral nematic phase was formed in DCM and chloroform in the concentration range 20–36%. Spherulites were formed in more concentrated solution. The formation of a LLC phase in polycarbodiimides organic solutions makes it possible to align the polymer helical chain to form an ordered film for electro-optical applications.     

Synthesis and lyotropic liquid crystal properties of chiral helical polycarbodiimides

Chiral helical polymers have been expected to exhibit optical activity with a significantly large optical rotation power. In this paper polymethylphenylethylcarbodiimides (Poly-PhEMCDI) with helical structure were synthesized by the insertion polymerization of a corresponding chiral monomeric carbodiimide initiated by a copper complex. The circular dichroism spectra and optical rotation power induced by the ordered rigid main chain helical structure of polycarbodiimides, in solution and as cast films, were studied. Polycarbodiimides have a rigid rod helical structure and form lyotropic liquid crystal (LLC) in organic solvents such as dichloromethane (DCM), chloroform and THF. The LLC phase was studied using polarizing optical microscopy and X-ray diffraction. A chiral nematic phase was formed in DCM and chloroform in the concentration range 20-36%. Spherulites were formed in more concentrated solution. The formation of a LLC phase in polycarbodiimides organic solutions makes it possible to align the polymer helical chain to form an ordered film for electro-optical applications.