MORPHOLOGICAL STUDY ON THE ORIENTED CHITOSAN FILM OBTAINED FROM PRE-SHEARED LIQUID CRYSTALLINE SOLUTION IN DICHLOROACETIC ACID

The oriented chitosan films obtained from pre-sheared liquid crystalline chitosan/dichloroacetic acid (DCA)solutions were studied by means of polarized optical microscopy (POM), scanning electron microscopy (SEM), infra-reddichroism technique and wide angle X-ray diffraction (WAXD). The shear induced band texture in the film was found tocorrespond to the sinusoidal fibrillar microstructure along the shearing direction on the basis of POM and SEM observations.The sinusoidal fibril was found to be lying within the film plane. The model of chitosan molecular orientation in the pre-sheared film with band texture can be established assuming that the main chain orients in the shearing direction and the sidegroup is perpendicular to the shearing direction. The WAXD azimuthal scanning at 2θ= 20° indicates that the (002) planeorients perpendicular to the shearing direction.     

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．     

光散射方法表征聚对苯二甲酰对苯二胺薄膜的结构特征

采用光散射方法研究了聚对苯二甲酰对苯二胺(PPTA)浓硫酸溶液于不同凝固条件下成膜时得到的球晶和草席晶等结构。PPTA的球晶由一些各向异性棒状微晶呈辐射型有序排列聚集而成的。红外二向色性的研究证明,PPTA草席晶中分子链沿“草席方向”高度取向。基于光栅衍射效应的角度依赖性认为,草席结构中条带的亮暗主要是由于它们取向方向上稍有差异引起的。以光栅效应计算了PPTA草席晶结构的长周期数据值及条带的取向状况,得到了较好的结果。根据在切应力作用下液晶的光散射图象认为,草席状结构是在切应力作用下于各向异性液业已形成,快速凝聚的方法可以把该种结构的特征保留在所获得的薄膜之中。     

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。     

Direct decoration of disclinations by solidification-induced band texture for a nematic side chain liquid crystalline polymer

For a nematic polymethacrylate side chain liquid crystalline polymer, g 154 N 298 I (°C), the solidification-induced band texture has been observed aligned along the disclination under a polarizing optical microscope, when the specimen was quenched from 280°C to room temperature. The decoration technique of solidification-induced band texture, which is usually reported for main chain liquid crystalline polymers, was then introduced to reveal the director field pattern along a disclination for this side chain liquid crystalline polymer. It was found by infra-red dichroism measurements that the director orientation is parallel with the direction of the band. On this basis, disclinations with strength s=±1/2 and s=±1 were mapped according to the corresponding pattern of solidification-induced band texture. In addition, two types of inversion wall, loop-like and splay-type walls, were also found to be decorated by the solidification-induced band texture.     

Polysiloxane side-chain liquid crystalline polymers prepared by alkyne hydrosilylation

We describe in this work an alkyne-hydrosilylation approach to synthesize a series of novel polysiloxane sidechain LCPs attaching end-on or side-on mesogenic side groups. Their properties are characterized by NMR, FTIR, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, polarized optical microscopy and small-angle X-ray scattering. These obtained alkenylsilane linked novel LCPs exhibit higher glass transition temperatures and clearing points, and especially display the tendency of forming smectic phases, in strong contrast with the nematic phases of their comparative conventional alkylsilane linked analogues, which manifests more rigid features of the alkenylsilane linkages and their significant influence on the mesomorphic properties.     

Band texture formation of sheared polymeric liquid crystalline state

The phenomenon of band texture formation of sheared main chain liquid crystalline polymers is reviewed. The bands seen in a polarizing microscope are optical effects. The macromolecular chains are aggregated into zig-zag bent fibrils perpendicular to the bands. The band texture is formed during shear relaxation. The induction period depends on the shear rate applied, the shearing time, solution concentration (lyotropic), solution layer thickness, temperature and the nature of the polymer. There exists a critical shear deformation to bring a multi-domain nematic or cholesteric phase into a monodomain continuous phase, from which the band texture is formed. These two phases show quite different rheological behavior. In certain cases randomly oriented regions of bands can also be formed during quenching of a thermotropic nematic polymer melt or during standing of a lyotropic nematic polymer solution, where the nematic domains in the melt or in the solution have grown to a sufficient size.     

Formation of band textures in hydroxypropylcellulose liquid crystals

Upon shearing, some polymeric liquid crystals develop a particular texture, called “band texture,” consisting of fine equidistant black lines as viewed between crossed polarizers. In mesomorphic hydroxypropylcellulose–water solutions, these bands are due to relaxation of the shear. The band texture appears after shearing at low shear rates and seems to exist during shearing at high shear rates (> 200 S^?1). In the latter case, the steady-state first normal-stress difference is negative. The bands relax in a few minutes and parts of the bands form elongated domains. This texture gives a H_v light-scattering pattern which can be interpreted by the theory of scattering by anisotropic rods. These domains lose their elongated shape with time.     

Hydrogen bond network formation

The signs of the dynamic dichroism of the NH stretch and the amide I bands in nylons were found to be counterintuitive. Experiments show that polymer chains tend to align in the direction of an applied tensile strain. The CH stretching bands in nylons exhibit the expected negative dynamic dichroism indicating chain alignment in the strain direction. The ΔA′ peaks for the NH and amide I bands are positive. The ΔA′ peak for the NH band is also unusual in that it has a derivative shape. This can be explained by band shifts brought about by anisotropic changes in the intermolecular spacing in the glassy polymer. Above T_g the derivative shape disappears but the ΔA′ peak for both the NH and amide I absorption remain positive. We postulate that the positive ΔA′ peaks of the NH and amide I bands result from a hydrogen bonding network where stress is transmitted through a network consisting of covalent chains connected by hydrogen bonds.     

条带织构装饰技术观察含T─型液晶基元的热致性聚芳酯液晶态的向错

采用条带织构装饰新技术研究了含Ｔ─型液晶基元的热致性聚芳酯液晶态的向错形态．经过培养的液晶样品无需剪切，淬火后便可呈现出围绕向错点取向排列的条带织构，而条带织构长轴的垂直方向正代表了液晶基元的指向矢方向，这样，在普通偏光显微镜下就能直接观察到这些条带织构装饰的强度Ｓ＝±１／２和Ｓ＝±１的向错，并观察到Ｓ＝－３／２的高强度向错和闭环状的反转壁．     

Long‐range orientation correlations and molecular alignment in sheared thermotropic copolyester. In situ light and X‐ray scattering

Orientation correlations induced by shear flow and their relaxation were investigated using in situ small‐angle light scattering (SALS) in the thermotropic random copolyester of 60 mol% hydroxybenzoic acid (B) and 40 mol% ethylene terephthalate (ET). B‐ET displays a nematic polydomain texture, the SALS and wide‐angle X‐ray scattering (WAXS) patterns are amorphous and isotropic. Shear flow produced optical defect multiplication with the consequent reduction of the micro–domains size. However, SALS detected long‐range spatial correlations within the optically chaotic texture, the SALS patterns showed bimodal orientation of defects. After cessation of shear the orientation correlation rapidly relaxed back to a polydomain and the SALS pattern became again isotropic. Above a threshold shear rate of about the SALS pattern showed unimodal orientation arising from line defects oriented nearly orthogonal to the velocity axis. Strikingly, the texture relaxation now showed the well known “banded texture”. The threshold shear rate coincided with a significant increase in the degree of molecular alignment as determined from in situ X‐ray scattering. This technique also showed that shear flow always oriented the molecular chains along the flow direction regardless of the shear rate. Copyright © 2007 John Wiley & Sons, Ltd.     

In situ poling and orientation stability of chromophore-bearing ladderlike polysiloxanes

A new, specially designed nonlinear optical (NLO) polymer is composed of ladderlike polysilsesquioxane as a backbone and “side-on or end-on” fixed stilbene chromophores. In-situ poling was carried out simultaneously during film formation via solvent evaporation and crosslinking which was caused by sequential hydrolysis and condensation of remained Si-H groups on macromolecules. The dipolar orientation after poling is described by an order parameter Φ which was measured using an original linear optical technique–UV dichroism. Orientation order and its decay are influenced by chromophore loading, crosslinking degree and poling condition. Compared with corresponding single chain polymers, a poled thin film of ladderlike NLO polymers demonstrates more stable poling-induced orientation.     

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.     

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.     

Rheo‐optical studies of the effect of shear flow on the structure of elastomer blends

The effect of shear flow on the structure of a phase‐separated, near‐critical blend of 50/50 (w/w) poly(styrene‐ran‐butadiene) and polybutadiene was studied with two different custom‐built rheo‐optical instruments that combined polymer melt flow and small‐angle light scattering (SALS). The deformation of the phase domains during shear flow was nonaffine, and the SALS patterns evolved from a spinodal ring (SR) pattern to a squashed SR with two high‐intensity lobes, to an H‐pattern, to a butterfly pattern with a dark streak along the equator, and finally to a steady‐state, elliptical pattern. The SALS patterns were explained in terms of a network model, in which the strands of the network first orient in the flow direction, then extend in this direction, and finally break up into droplets aligned in the flow direction. According to this picture, the strands in the vorticity direction do not deform until relatively high strains, after which the periodicity of the network begins to disappear. Supporting this model was the observation that the transitions between the different SALS patterns corresponded to inflections and/or maxima in the shear stress or first normal stress difference. Increasing the shear rate changed the kinetics of the structure evolution and reduced the size of the phase‐separated droplets in the steady state. No evidence was obtained for flow‐induced miscibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1725–1738, 2004     

Molecular design of liquid crystalline poly(ester-amide)s with perfluoroalkyl spacers

We have introduced a series of perfluoroalkyl dicarboxylic acids with different lengths of fluorinated aliphatic segments into the 2,6-acetoxynaphthoic acid (ANA) and acetoxy acetanilide (AAA) systems; and their effects on the evolution of liquid crystal texture and liquid crystallinity have been investigated. The perfluoroalkyl dicarboxylic acids are tetrafluorosuccinic acid (TFSA, n=2), hexafluoroglutaric acid (HFGA, n=3), perfluorosuberic acid (PFSUA, n=6) and perfluorosebacic acid (PFSEA, n=8). Computational results based on the 'RIS' Metropolis Monte Carlo method indicate that the ANA/AAA/perfluoroalkyl system may form thermotropic liquid crystalline polymers (LCPs) because the calculated persistence ratios are greater than 6.42. Computational results also predict that the systems containing even-numbered perfluoroalkyl acids have greater persistence length and molar stiffness than that containing odd-numbered acids. Experiments were carried out using the in situ thin film polymerization technique under a polarizing optical microscope. We observed that systems containing short aliphatic units (n=2, 3) tend to remain in the LC phase, while systems containing a long aliphatic spacer (n=8) tend to crystallize during the late stage of the polycondensation reaction. The liquid crystal domain formed in the early stage has a disclination strength S of +1. Ternary phase diagrams were plotted to show the relationship among monomer structure, composition, anisotropic and crystalline phases. FTIR results confirm the formation of LCPs.     

Development of orientation and texture during shearing of liquid-crystalline polymers

Using polarizing microscopy, we study the development of orientation and texture during slow shearing of liquid-crystalline solutions of poly(γ-benzyl-L-glutamate). Shearing of high molecular weight samples that are initially coarsely textured, or are uniformly oriented over regions of 1 mm², produces a steady state striped texture, for each of three different initial average orientations. The director field in the striped texture is on average aligned parallel to the flow direction, but with misalignment that varies periodically as we move in a direction orthogonal to flow, thus giving the sample a striped appearance under crossed polarizers, with stripes parallel to flow. After the stripes form, they become finer with increased shearing, or with increased shear rate. Along with the birefringent stripes, there are defect lines, parallel to the flow direction with a spacing similar to that of the stripes, i.e. 10 μm or less at steady state. The existence of separate time scales for the development of steady state orientation, and for the shrinkage of the texture length scale to a steady state, is consistent with a phenomenological scaling theory that had been postulated to explain the rheological behaviour of these fluids. Although the steady state striped texture is independent of initial orientation, transient textures during start-up of shearing are highly dependent on initial orientation; for some initial orientations, bands perpendicular to flow occur temporarily during shearing.     

MORPHOLOGY OF A THERMOTROPIC AROMATIC POLYESTER

The crystalline morphology of a thermotropic aromatic polyester has been studied by microscopy techniques. Spherulites with ringed structure under polarizing micioscope were observed for solution cast specimens, They were composed of radially growing crystalline lamellae of thickness around 100. It was found that the molecules were packed in the thickness direction. Banded texture was observed in randomly packed domains for melt cast specimens. The bands have the same width and internal structure as those usually observed in oriented specimens of these polymers obtained by shearing their mesomorphic melt.     

Spiralling optical morphologies in spherulites of poly(hydroxybutyrate)

Some rather unusual optical morphologies in thin films of poly(hydroxybutyrate) in which a temperature gradient is imposed across the thickness of the film are reported. Spherulites in which the Maltese cross degenerates into a continuous spiral grow under these conditions, and the direction of the rotation of the spirals depends on the direction of heating. These morphologies are explained with the existing understanding of spherulite optics. The helicoidally twisting crystallites are modeled as twisting around an axis at a fixed angle to the radius of the spherulite (and the plane of the film). The possible implications for future, inclusive models of banding in spherulites are discussed. Further observations on the temperature dependence of the optical banding pattern in poly(hydroxybutyrate) are also reported, and an unexpected minimum in band spacing and fine optically visible fibrillar texture is discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1575–1583, 2000