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1.
A novel hyperbranched polyimide (HPPI) was synthesized from a new four‐functional amine and 1,2,3,4‐cyclobutanetetracarboxylic dianhydride. The polyimide with hyperbranched structure exhibited excellent alignment for nematic liquid crystal (LC) compared with traditional linear polyimides. The solution viscosities of the poly(amic acids) (PAAs) and the surface morphology of PI films were investigated using an Ubbelhode‐type viscometer and atomic force microscopy, respectively. The viscosities of the hyperbranched PAAs were much lower than that of the linear PAA solution at any monomer ratio (amine:dianhydride). Pretilt angles of LCs above 2.8° were achieved with HPPI. 相似文献
2.
We propose a novel method for homeotropic alignment of liquid crystals (LCs) utilising in situ self-assembly of a low concentration of 4-(4-heptylphenyl)benzoic acids that form hydrogen bond with the indium tin oxide (ITO) substrates. Stable homeotropic alignment in the LC device is achieved with a simple mixing process of benzoic acid derivative in LC media, and it yields electro-optical performance similar to that achieved with the conventional alignment method using polyimides. It is experimentally confirmed that an ultrathin self-assembled molecular layer of 4-(4-heptylphenyl)benzoic acid formed by hydrogen bonding on ITO substrate makes it possible to attain a reliable homeotropic alignment of LCs. Furthermore, this simple approach provides a cost-effective and stable LC alignment layer with fast response time and thermal stability. 相似文献
3.
A novel functional diamine N12, containing triphenylamine moiety, biphenyl, tert-butyl substituents and long alkyl chain, N,N-bis(4-aminophenyl)-p-(3,5-di-tert-butyl-4-dodecyloxy phenyl) aniline (N12), was synthesised and characterised. A series of polyimides (PIs) were prepared based on 2,2?-bis(trifluoromethyl)benzidine, 4,4?-oxydiphthalicanhydride and different contents of N12 via a conventional two-step procedure that included a ring-opening polyaddition to gain polyamic acids, followed by chemical cyclodehydration. The chemical structures of the intermediates, diamines and PIs were characterised by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. All of the PIs were amorphous and exhibited good solubility in both polar aprotic solvents and some low boiling point solvents. PIs containing different content of N12 could induce highly uniform vertical alignment of liquid crystals (LCs). More importantly, PIs derived from N12 showed a good rubbing resistance. Besides, all PI films showed high transmittance in the wavelength range 400–700 nm and good thermal stabilities. Such PIs could be suitable candidates for alignment layers used in the manufacture of high-performance vertical alignment mode LC displays. 相似文献
4.
The transition from the homeotropic to the planar state in cholesteric liquid crystal displays is investigated through computer simulation. The simulation reproduces the observed relaxation from the homeotropic state to the long pitch transient planar state. The simulation also agrees with the suggestion that the transition from the transient planar state to the planar state proceeds through a bulk modulation resulting in folding and buckling of cholesteric layers without introduction of defect cores. The model obtained agrees well with earlier experimental observations showing that the process includes a tilting of cholesteric helices, and that the surface plays only a minor role in the relaxation process. 相似文献
5.
Thermo-recording in a [side chain type smectic A liquid crystal polymer (SmA-LCP)/nematic liquid crystal (N-LC)/chiral dopant/dichroic dye] composite has been realized by using 2mW of power from a He-Ne laser. The laser irradiation-induced phase transitions of smectic A (SmA) → chiral nematic (N*) → SmA formed the dominant thermo-recording mechanism in the composite. Thermo-recording in the (SmA-LCP/N-LC/chiral dopant/dichroic dye) composite exhibited a higher contrast when compared with the non-polymeric (SmA-LC)/N-LC/chiral dopant/dichroic dye composite. 相似文献
6.
We propose a novel method to fabricate a vertical alignment (VA) of liquid crystal (LC) molecules without using a conventional alignment layer such as polyimide film. The method produces the vertical alignment polymer layer (VAPL) by polymerisation of a monomer or mixed monomers including in the LC layer above TNI of the LC material. The VA mode LC cell with the VAPL (VAPL-LC cell) produced from the mixed monomers of acrylic acid 4-(4?-octyloxy-biphenyl-4-yloxy)-butyl ester and 1,2-bis-(4-methacryloxy-phenyl)-2,2-dimethoxy-ethane-1-one exhibited enough level of alignment state and electro-optical property with high voltage holding ratio. We can expect that the VAPL-LC cell is useful for next-generation displays such as flexible liquid crystal displays because the method does not need the process including high temperature over 200°C. 相似文献
7.
Gang Zhu Fei Wang Wenjie Liu Xinjian Gong Pengfei Geng Zhenwei Gao 《Liquid crystals》2020,47(4):489-499
ABSTRACTA new photosensitive polyimide (PI) was successfully synthesised via esterification of PI containing hydroxyl groups with cinnamoyl chloride (CL). The cinnamate (CA) group contents of the PI was up to 90%. The PI films could induce uniform parallel alignment of liquid crystal (LC) molecules after the non-polarised ultraviolet ageing lamp exposure, which reduce the cost significantly compared with polarised ultraviolet light equipment. In addition, the PI exhibited good thermal stability. Meanwhile, the possible mechanism of PI alignment films induced by NPUVL was discussed in some detail. 相似文献
8.
David J. Abdallah Liangde Lu T. Matthew Cocker Robert E. Bachman Richard G. Weiss 《Liquid crystals》2013,40(6):831-837
The first single crystal structure of a Group VA halide salt with three equivalent long n-alkyl chains, benzyltrioctadecylammonium bromide (BzN18Br), is reported. It consists of alternating interdigitated and non-interdigitated regions of alkyl chains separated by ionic planes. Two chains per molecule are paired and extend to one side in a non-interdigitated region. The third chain is on the opposite side of the ionic plane and pairs intermolecularly to form an adjacent, interdigitated region. The thickness of two nearly extended molecules defines the bilayer unit-two ionic planes flanked by a region with intramolecularly paired chains and separated by an interdigitated chain region. Powder X-ray diffraction and optical microscopy data of liquid crystalline BzN18Br are consistent with an enantiotropic smectic A2 (SmA2) phase: the three n-alkyl chains of each molecule are projected from one side of an ionic plane, and head groups of neighbouring molecules are oriented head-to-head, in a non-interdigitated bilayer assembly. The structure of BzN18Br fills an important gap in our knowledge about the crystal packing of ammonium and phosphonium salts with one-four equivalent long n-alkyl chains. A comparison of their packing arrangements is made and the transitional nature of the BzN18Br structures is demonstrated. Although salts with one, two, or three long n-alkyl chains form SmA2 phases, each is distinctive in its molecular packing. A large molecular reorganization accompanies the crystal-to-liquid crystal transition of BzN18Br. 相似文献
9.
Hyo Kang Hyunkee Hong Dong-Gyun Kim Eun-Ho Sohn Jimin Shim Daeseung Kang 《Liquid crystals》2013,40(1):32-40
A series of poly(methyl methacrylate) derivatives containing polyhedral oligomeric silsesquioxane (POSS) groups (MCP#) were synthesised via free radical polymerisation (FRP) using methacryl isobutyl POSS (MA-POSS) and methyl methacrylate as monomers to investigate liquid crystal (LC) alignment property of these polymer films. The LC cells made from the films of the polymers having 100 mol% of MA-POSS units (MCP100) showed vertical LC alignment having a pretilt angle of about 90°. The vertical LC alignment behaviour on the MCP100 film was ascribed to the very hydrophobic MCP100 surface having the surface energy value smaller than about 23 mJ/m2 generated by the nonpolar bulky POSS group. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), were observed for the LC cells fabricated using MCP100 as a LC alignment layer. 相似文献
10.
Preparation and characterization of a novel polyimide liquid crystal vertical alignment layer 总被引:1,自引:0,他引:1
Zhijie Liu 《European Polymer Journal》2008,44(8):2718-2727
A series of diamines with a side chain containing rigid biphenyl unit and nonpolar alkoxy side end group [4-alkoxy-biphenol-3′,5′-diaminobenzoate] (Cm-BBDA, m = 4, 6, 12) were synthesized and their chemical structures were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and nuclear magetic resonance spectroscopy (1H NMR). Then three polyimides (PIs) were prepared by copolymerization of pyromellitic dianhydride (PMDA), 4,4′-methylenedianiline (MDA) and Cm-BBDA in N-methyl-2-pyrrolodone (NMP), and chemical structures of all PIs were confirmed by FT-IR. Structural identification of all poly(amic acid)s (PAA) was performed by 1H NMR. Liquid crystal (LC) cells were fabricated using these PIs as the alignment layer for characterization of the alignment properties of LCs. It was found that the planar alignment was obtained when PI with side chain containing alkoxy side end group of 4 carbon atoms was employed and the vertical alignment was observed when alkoxy side end groups of 6 or 12 carbon atoms were included. A uniform vertical alignment was validated by polarizing microscopy. It was testified that LC vertical alignment possessed high thermal stability. 相似文献
11.
A series of soluble and highly transparent semi‐alicyclic polyimides (PIs) with designed flexible linkages have been synthesized derived from an alicyclic aromatic dianhydride (1,2,3,4‐cyclobutanetetracarboxylic dianhydride, CBDA) and various aromatic ether‐bridged diamines. The semi‐alicyclic PIs were evaluated as the photo‐alignment layers of liquid crystal (LC) molecules in liquid crystal display (LCD). Experimental results indicate that the photo‐alignment characteristics of LC molecules induced by the photo‐aligned PI layers and the electro‐optical (EO) properties of the LC cell devices are closely related with PI backbone structures. The retardation of the photo‐aligned PI layers is correlated with the ultraviolet (UV) absorption intensity of PI at 220 to approximately 330 nm. The higher UV absorption intensity PI has, the higher retardation and lower pre‐tilt angle the photo‐aligned PI layer exhibits. The defect‐free and photo‐aligned PI layer could result into the uniform LC texture, which is highly desired for in‐plane switching (IPS) mode LCD devices. In comparison, PI layer containing trifluoromethyl moiety shows poor photo‐aligning performance because of the strong electronic withdrawing effect of the fluorinated linkage. 相似文献
12.
S. I. Kim M. Ree T. J. Shin J. C. Jung 《Journal of polymer science. Part A, Polymer chemistry》1999,37(15):2909-2921
New poly(m-phenylene 4,4′-oxydiphthalimide)s containing various side chains, such as 6-(4-biphenylmethoxy)hexyloxy group and 6-(phenylphenoxy)hexyloxy isomers, were synthesized, giving thin films of a high quality. All the polyimides apparently were almost amorphous, but exhibited short-range ordering in some extent, depending on the side chains. By incorporating side chains, the thermal properties, including stability, thermal expansivity, and glass transition temperature, were generally degraded, whereas the optical and dielectric properties were improved. All the polyimides exhibited a good rubbing processability and excellent performance in the controlling of both the alignment and the pretilt of LC molecules in the LC cell. The pretilt angle of LC molecules was easily achieved in a wide-angle range of 8–27°, depending upon the rubbing density as well as the incorporated side chains. The pretilting of LC molecules was very sensitive to all the molecular parameters (namely, the flexibility of polymer chain backbone as well as the isomeric structure of biphenyl mesogen end group, spacer length, and spacer conformation in the side chain) in the polyimide, in addition to the rubbing process. In particular, the side chains, which are much shorter in length than the long alkyl side chains in the polyimides being used widely as LC alignment layers, were evident to involve effectively in the alignment of and the pretilt of LC molecules, which are highly desired in the LC display industry. This might mainly be attributed to a strong interaction between the biphenyl mesogen end group of the side chain and the LC molecule. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2909–2921, 1999 相似文献
13.
Jan P. F. Lagerwall Per Rudquist Sven T. Lagerwall Frank Gießelmann 《Liquid crystals》2013,40(4):399-414
The substance MHPOBC is the oldest and still most important reference antiferroelectric liquid crystal (AFLC). There is still considerable controversy concerning the correct phase designations for this material and, in particular, about the presence or absence of SmC* in its phase sequence. By means of dielectric spectroscopy and polarizing microscopy, we show that whereas the pure compound lacks the SmC* phase, this phase rapidly replaces the SmC*β subphase through the reduced purity resulting from temperature-induced chemical degradation which is hard to avoid under standard experimental conditions. X-ray investigations furthermore show that this change in phase sequence is coupled to a decrease in translational order. This explains the large variations in the reported phase sequence and electro-optic behaviour of MHPOBC, in particular concerning the SmC*β phase which has been said to exhibit ferro-, ferri- as well as antiferroelectric properties. It is likely that the sensitivity of the AFLC phase sequence to sample purity is a general property of AFLC materials. We discuss the importance of optical and chemical purity as well as tilt and spontaneous polarization for the observed phase sequence and propose that one of the key features determining the existence of the different tilted structures is the antagonism between orientational (nematic) and translational (smectic) order. The decreased smectic order (increased layer interdigitation) imposed by chemical impurities promotes the synclinic SmC* phase at the cost of the AFLC phases SmC*α, SmC*β, SmC*γ and SmC*a. We also propose that the SmA* phase in FLC and AFLC materials may actually have a somewhat different character and, depending on its microstructure, some of the tilted phases can be expected to appear or not to appear in the phase sequence. AFLC materials exhibiting a direct SmA* -SmC*a transition are found to be typical ‘de Vries smectics’, with very high orientational disorder in the SmA* phase. Finally, we discuss the fact that SmC*β and SmC*γ have two superposed helical superstructures and explain the observation that the handedness of the large scale helix may very well change sign, while the handedness on the unit cell level is preserved. 相似文献
14.
Masanobu Mizusaki 《Liquid crystals》2013,40(8):1167-1174
Two series of asymmetric banana-shaped compounds have been synthesized and studied. In the 1,3-phenylene bis[4-(4′-alkoxybenzoyloxy)]benzoate series the lack of symmetry was derived solely from the difference in length of the two terminal alkoxy chains. In the 3,4′-biphenylene bis[4-(4′-alkoxybenzoyloxy)]benzoate series the asymmetric nature originates from the 3,4′-substitution of the central biphenyl group and from the difference in length of the two terminal chains. All the melting points of the asymmetrical compounds in the series with the central phenyl unit are lower than those of the symmetrical compounds. The liquid crystalline B1 or B2 phase was retained in all cases. In the series with the central biphenyl unit the compounds with the shortest chain attached to the para-position of the central biphenyl unit have the lowest melting points. A significant lowering of the melting points in comparison with the symmetrically substituted compounds, however, could not be achieved. All the compounds of both series show a layer spacing which is comparable to those of the symmetrically substituted parent compounds. The observed switching behaviour of both the symmetric and asymmetric compounds with a B2 phase was antiferroelectric. 相似文献
15.
C. R. Gautreaux J. R. Pratt T. L. St. Clair 《Journal of Polymer Science.Polymer Physics》1992,30(1):71-82
A new polyimide derived from 4,4′-isophthaloyldiphthalic anhydride (IDPA) and 1,3-bis(4-aminophenoxy-4′-benzoyl)benzene (1,3-BABB) having semicrystalline behavior was prepared at NASA Langley Research Center in 1987. The crystalline transitions of this thermoplastic polyimide have been studied. The differential scanning calorimetry (DSC) pattern of partially imidized film exhibited two distinct crystalline melt endotherms. For this study each crystalline phase was isolated and enhanced by controlled thermal treatment. A film containing approximately 50% of both phases and an amorphous film were also prepared. Evaluations of these films were performed by DSC, wide-angle x-ray scattering (WAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Three distinct crystalline morphologies; ellipsoid, cubic, and needlelike embedded in an amorphous matrix were observed as a function of various cure conditions by SEM. 相似文献
16.
An in situ self-assembled molecular layer of 1-pyrenesulfonic acid sodium salt as an alignment agent was formed on indium tin oxide substrates for vertically aligning liquid crystals (LCs). The thus-aligned LCs exhibited uniform vertical alignment under crossed polarisers. The electro-optical characteristic of the LC cell fabricated using this method exhibited better performance than those of conventional LC cells with a polyimide alignment layer. Because the proposed alignment method is a simple one and involves low concentrations of the alignment agent (0.05 wt%), it is highly cost-effective. Further, the pyrene derivative, when mixed with LCs, exhibited photoluminescence (PL) under ultraviolet light. Given that the proposed method resulted in highly vertically aligned LCs and the alignment agent exhibited PL, the method should find wide use in the fabrication of colour-filter-free LC displays. 相似文献
17.
We synthesised a series of vitamin-based and renewable tocopherol-substituted polystyrene (PTOC#, # = 20, 40, 60, 80 and 100), where # is the molar content of tocopherol moiety, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a higher molar content of tocopherol side group showed vertical LC alignment behaviour. The vertical alignment (VA) behaviour was well correlated with the surface energy value of these polymer films. For example, VA was observed when the surface energy values of the polymer were smaller than about 35.22 mJ/m2 generated by the nonpolar tocopherol moiety having long and bulky carbon groups. Good electro-optical characteristics, such as voltage holding ratio and residual DC voltage, and aligning stabilities at 200°C and ultraviolet irradiation of 10 J/cm2 were observed for the LC cells fabricated using PTOC100 as a LC alignment layer. Therefore, it was first found that the renewable tocopherol-based materials can produce an eco-friendly vertical LC alignment system. 相似文献
18.
Lars Holländer Wilhelm Kossack Matthias Kollosche Werner Wirges Friedrich Kremer Reimund Gerhard 《Liquid crystals》2016,43(10):1514-1521
Polymer-dispersed liquid crystals (PDLCs) of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and nematic 4-cyano-4?-n-hexylbiphenyl (6CB) or 4-cyano-4?-n-pentylbiphenyl (5CB) were prepared to study the effect of the remanent polarisation of the polymer on the liquid crystal alignment. We measured the macroscopic alignment of the liquid crystal molecules in the thickness direction by means of Infrared Transition-Moment Orientational Analysis. Electrical poling at 100 V/µm caused an increased order parameter up to 0.15. After subsequent annealing above the nematic-to-isotropic phase-transition temperature, the order parameter was reduced to 0.02. Nevertheless, the order parameter was still higher than for non-poled film indicating a slight orientation in thickness direction. Both values are lower than those expected from model calculations. In agreement with dielectric measurements, we attribute this result to the shielding effect of mobile charge carriers within the liquid crystal inclusions. 相似文献
19.
20.
Chul‐Ho Ok Byoung‐Yong Kim Byeong‐Yun Oh Young‐Hwan Kim Kang‐Min Lee Hong‐Gyu Park 《Liquid crystals》2013,40(12):1373-1377
The nematic liquid crystal alignment capability and electro‐optical (EO) performance characteristics of in‐plane switching (IPS) cells were first demonstrated on organic hybrid overcoat layers via ion beam irradiation. Usually the organic hybrid overcoat is used as the material for making a plate alignment layer in a colour filter process. To characterise the organic hybrid overcoat layer, we analysed the surface composition of the organic hybrid overcoat by X‐ray photoelectron spectroscopy. The results show that the intensity of C = O and C–O bonding undergoes a change corresponding to the changes in energy of the ion beam exposure. Moreover, EO performance characteristics of IPS cells on the organic hybrid overcoat layer via ion beam irradiation were observed to have similar characteristics to the polyimide. 相似文献