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1.
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. 相似文献
2.
《Liquid crystals》2001,28(3):451-455
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. 相似文献
3.
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. 相似文献
4.
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. 相似文献
5.
6.
Zhongming Hu Shouxi Chen Shufan Zhang Renyuan Qian 《Macromolecular rapid communications》2000,21(15):1028-1031
A new decoration method termed as focal‐conic texture decoration has been established to map the director field of disclinations of nematic mesophases for a side‐chain liquid crystalline polymer (SCLCP) based on its transition from nematic to smectic phase with focal‐conic texture observed under a polarizing optical microscope. FT‐IR microscopy was used to ascertain the relationship between the mesogenic orientation direction and the orientation direction of focal‐conic texture, which exhibits consequently the director field of a disclination. 相似文献
7.
8.
Wei Wang 《Liquid crystals》1994,16(2):343-348
The transmission electron microscope technique enables direct visualization of disclination core structure of main chain liquid crystalline polymers. Generally, the lamellar structure, that is a function of type of polymer and molecular length, and of which the thickness is 10-200 nm, can be observed. In terms of distortions in the director field produced by a disclination, the elastic anisotropy, ε, can easily be calculated. However, the ε does not indicate the molecular distortion produced by the disclination. Continuum mechanics is used to describe the relationship between the elastic anisotropy, εa, measured from the lamellar director and that, εb, of the molecular director in main chain liquid crystalline polymers. The relationship is εa = -εb, indicating that lamellar distortion is completely different from the molecular distortion. 相似文献
9.
A series of main chain liquid crystalline ionomers containing sulphonate groups pendent to the polymer backbone were synthesized by an interfacial condensation reaction of 4,4'-bis(1,10-sebacyloxo)benzoic acid, brilliant yellow (BY), and 4,4'-biphenyldiol. 4,4'-Bis(1,10-sebacyloxo)benzoic acid exhibited nematic schlieren texture during heating and cooling. The ionomers are thermotropic liquid crystalline polymers and thermally stable to about 270°C. They exhibit broad mesophase regions over a range of 220°C and the same nematic mesomogen with a colourful thread texture as B0-LCP, which implies that the introduction of an ionic group did not change the texture of the B0-LCP. However, the thermotropic liquid crystalline properties were somewhat weakened when the concentration of BY was more than 5%. The inherent viscosity in N,N-dimethylformamide solution suggested that intermolecular associations of sulphonate groups occurred at low concentration, and intermolecular associations predominated at higher concentration. 相似文献
10.
Polarizing optical microscopy is employed to study director fields around disclinations in side-chain liquid crystalline polymer films. Optical black brushes together with stripes around disclinations are observed. The stripes run parallel to the local director and thus decorate overall patterns of nematic director around disclinations. Three director patterns involving radial, spiral, and circular microstructures of a positive integer disclination with s = +1 and one hyperbolic pattern of a negative integer disclination with s = -1 are observed in the thin film. It is found that the specific configurations of a pair of (+1, -1) disclinations form during the late stage of annihilation. Increasing the film thickness leads to disclination instability. We observe that black four-brushes of disclinations with s = +/-1 split into black two-brushes, where two types of director patterns of disclinations with half-integer strengths of s = +/- 1/2 produce. Theoretical analysis is presented to explain this instability. 相似文献
11.
Cloud point curves (CPC) have been measured for 1–4 cis polybutadiene (Mr = 40,000–830,000) in n-hexane, 2-methyl-hexane, 2,2,3 trimethylbutane and 2,2,4 trimethylpentane. These four systems show upper and lower critical solubility temperatures which approach one another as the molecular weight increases. An hourglass-shaped CPC is found for two systems. The CPC are found to be much more dependent on polymer concentration than is usual. Calculated (Prigogine, Patterson, Flory theories) and experimental critical temperatures, critical volumes and shapes of the CPC are in much better agreement for these systems than for other systems involving polystyrene, polyisobutylene or polybutene-1. Analysis of these results with those for other systems in the literature indicates the importance of the surface-to-volume ratio s of the polymers. A small value of s = s2/s1 (0·5–0·8) for thick polymer chains improves the calculated value of the critical temperature while s = 1 is quite good for thin polymer chains such as polybutadiene and polyethylene. 相似文献
12.
A new method for the study of texture and director patterns in a main chain thermotropic aromatic copolyester with a flexible spacer is described, whereby the molecular chain or director orientation of the nematic mesophase becomes decorated by the formation of a banded texture during quenching, without being subjected to a shear. The pattern of the decorated banded texture may be observed directly by polarizing optical microscopy, revealing the complete texture of molecular chain orientation across the whole specimen. The molecular director orientation lies perpendicular to the long axis of the bands. Various types of disclination, including an inversion wall, in the nematic mesophase of a thermotropic aromatic copolyester have been observed. This decorating technique is particularly suited for non-crystallizable main chain liquid crystalline polymers, where the lamellar decoration technique fails. 相似文献
13.
Zhang S Terentjev EM Donald AM 《Langmuir : the ACS journal of surfaces and colloids》2005,21(8):3539-3543
Atomic force microscopy (AFM) is employed to study the supermolecular microstructures of disclinations and inversion walls in thin films of a smectic side-chain liquid crystalline polymer. Two-dimensional nanostripes are formed in thin films when the material enters the smectic phase. A possible mechanism for their formation is also suggested. The stripes run parallel to the local director and thus decorate the overall patterns of nematic director around the disclinations and inversion walls. Three patterns involving radial, spiral, and circular supermolecular microstructures of a positive disclination with s = +1 and one hyperbolic pattern of a negative disclination with s = -1 are observed. The cores of all these microstructures exhibit circular dark centers in AFM height images. It is found that the specific configurations of a pair of (+1, -1) disclinations form during the late stage of annihilation and inversion walls always separate a pair of (+1, +1) disclinations. The analysis on the director fields around disclinations and inversion walls shows that the bend and splay elastic constants are of the same order of magnitude in the side-chain liquid crystalline polymer. 相似文献
14.
Robert J. Twieg Vano Chu Cattien Nguyen Christine M. Dannels Christopher Viney 《Liquid crystals》1996,20(3):287-292
The liquid crystalline phases of several rigid-rod, non-polar tolane oligomers are characterized by differential scanning calorimetry and transmitted polarized light microscopy. We determine that a stable nematic phase can be formed at ambient pressure if the molecular axial ratio (length-to-width ratio) is greater than 4.5. A smectic phase forms in addition to the nematic phase if the axial ratio exceeds 6.1. Symmetrical fluorination of the terminal phenyl groups reveals that the liquid crystalline phase behaviour of these rigid rods is highly sensitive to perturbations of the charge distribution along the molecules. Nematic tolane oligomers can exhibit high stregth disclinations (s = ±3/2 and ±2) in their schlieren textures, and we discuss conditions that promote the stability of these defects. 相似文献
15.
Wei Wang 《Liquid crystals》2013,40(2):343-348
Abstract The transmission electron microscope technique enables direct visualization of disclination core structure of main chain liquid crystalline polymers. Generally, the lamellar structure, that is a function of type of polymer and molecular length, and of which the thickness is 10–200 nm, can be observed. In terms of distortions in the director field produced by a disclination, the elastic anisotropy, ?, can easily be calculated. However, the ? does not indicate the molecular distortion produced by the disclination. Continuum mechanics is used to describe the relationship between the elastic anisotropy, ?a, measured from the lamellar director and that, ?b, of the molecular director in main chain liquid crystalline polymers. The relationship is ?a = ??b, indicating that lamellar distortion is completely different from the molecular distortion. 相似文献
16.
高分子液晶态向错结构在正交偏振片下呈现出具有不同数目黑刷子的纹影织构,是由于分子指向矢取向排列上的不连续性所引起的一种光学效应。近年来,高分子液晶态向错结构的研究已取得了较大进展,发展和应用片晶装饰、条带织构装饰和表面裂纹装饰等技术可以在电镜和偏光显微镜下直接观察各种向错结构。本文简要介绍高分子液晶态向列相的向错和反转壁结构的几何学、高强度向错以及近年在实验上观察各类型向错形态的研究进展。 相似文献
17.
Masanori Matsui Yuji Yamane Hideaki Kimura Shigeki Kuroki Isao Ando Kai Fu Junji Watanabe 《Journal of Molecular Structure》2003,650(1-3):175-180
Solid state 13C NMR experiments on poly(p-biphenylene terephthalate) with long n-dodecyl side chains have been carried out over a wide range of temperatures, in order to elucidate conformational and dynamical behavior of the polyester in the crystalline state and thermotropic liquid crystalline state. From these experimental results, it is found that at temperatures from room temperature to 80 °C the n-alkyl side chains take both of the immobile and the mobile regions, and at temperatures above 120 °C take only the mobile region. In the immobile region the n-alkyl side chains are in the all-trans zigzag conformation and in the mobile state are undergoing fast exchange between the trans and gauche conformations. On the other hand, the terephthalate moiety of the main chain undergoes rotational motion after the melt of n-alkyl side chains as the temperature is increased. 相似文献
18.
Zulema Chaia Andr s Zelcer Bertrand Donnio Marcia Rusjan Fabio D. Cukiernik Daniel Guillon 《Liquid crystals》2004,31(7):1019-1025
Two series of polymeric mixed-valent diruthenium (II,III) aliphatic carboxylates of formula Ru2[O2C(CH2)n-2CH3]4X (where X=dodecylsulfate (DOS) anion and n=8, 9, 16 and 18, or X=octylsulfonate (OS) anion and n=8, 10, 12, 14 and 18) were synthesized and characterized. Their liquid crystalline properties and crystalline (Cr) structures were analysed; the Cr phases are lamellar in all cases. For long chain DOS derivatives (n=16 and 18) hexagonal and rectangular columnar mesophases (Colh and Colr) with melting temperatures close to 140°C were observed. For long chain OS derivatives (n≥10) a Colh mesophase was observed, with melting temperatures between 140 and 190°C. 相似文献
19.
We have microscopically observed the textures of very large droplets of cholesteric liquid crystal in a polymer matrix under the influence of an electric field E. When E = 0, the droplets exhibit rings and often a disclination line extends from the centre to the periphery of the droplet. As E increases, the droplet undergoes a progressive transition to a uniform-appearing texture. This uniform region first occurs near the centre of the droplet, then increases in radius as the field is increased. We propose that the field-off texture corresponds to the Frank-Pryce spherulite model while the uniform field-on texture is the planar texture. 相似文献
20.
An intensive study has been conducted to map the director fields of disclination of nematic liquid crystalline copolyesters. In this study, films of two wholly aromatic main-chain polyesters containing para- (ABA/MH/TFTA) and meta-linkages (ABA/MH/TFIA) (ABA, p-acetoxybenzoic acid; MH, maleic hydrazine; TFTA, tetrafluoroterephthalic acid; TFIA, tetrafluoroisophthalic acid) were synthesized to investigate the effects of kinks on liquid crystallinity, disclination strength (S), and surface microcracks decoration. These two copolyesters were prepared by in-situ thin film polymerization and characterized by polarizing light microscope, wide-angle X-ray diffraction, as well as "rotational isomeric states" (RIS) Metropolis Monte Carlo (RMMC) simulation. An optical microscope shows that the surface microcracks forms in the nematic-mosaic texture during a rapid quenching. The ABA/MH/TFTA film exhibits disclination strength with S = +1 and S = -(1)/(2); however, disclination strengths with S = +/-1 have been observed in the ABA/MH/TFIA system. To our best knowledge, this is the first paper reporting the effects and evidence of kink (meta and para moieties) on topological defect of disclination. In addition, the RMMC analysis supports the liquid crystal formation in both polyester films with a persistence ratio greater than 6.42. 相似文献