Synthesis and properties of photochromic cholesteric liquid crystalline polysiloxane containing chiral mesogens and azobenzene photochromic groups

A series of novel thermotropic side‐chain liquid crystalline polymers(P₀–P₁₂) were synthesized by grafting copolymerization of mesogenic monomer cholesteryl undecylenate (M1) and photochromic monomer 4‐allyoxy‐4′‐nitroazobenzene (M2) on polymethylhydrosiloxane. The chemical structures of polymers were characterized by infrared (IR) and ultraviolet (UV) spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by polarized optical micrograph, DSC, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The glass transition temperatures (T_gs) of the polymers increased from P₀ to P₄ and decreased from P₅ to P₁₂. The clearing point temperatures (T_is) of the polymers P₁–P₁₂ were lower than that of P₀, but increased from P₁ to P₄ and decreased from P₅ to P₁₂. They showed thermotropic liquid crystalline properties in a broad mesogenic region at temperatures >100°C. The polymers P₀–P₈ exhibited a cholesteric mesophase with oily streaks and lined texture, and polymers P₉–P₁₂ showed a chiral smectic mesogenic phase with a layered texture. All of the polymers were thermally stable to ～ 320°C. The UV‐induced trans–cis photoisomerization was investigated for the azo monomer and polymers P₈ and P₁₂. The solution of the azo monomer and liquid crystalline polymers P₈ and P₁₂ can undergo photoisomerization, and the environments of the azo group were responsible for the aforementioned photochemical process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2155–2162, 2002     

Synthesis and chiroptical properties of liquid crystalline copolymers containing azobenzene chromophores

A series of new liquid crystalline copolymers, poly[((S)‐2‐methyl‐1‐butyl methacrylate)‐co‐(6‐(4‐(4‐cyanophenylazo)phenoxy)hexyl methacrylate)], with different contents of chiral units of 17, 36, 54 and 78 mol% were synthesized. The structures and properties of the copolymers were characterized and evaluated using infrared, ¹H NMR and UV spectroscopy, differential scanning calorimetry, gel permeation chromatography and circular dichroism (CD). The CD results suggested that absorptions of azobenzene chromophores were observed in films of copolymer containing 17, 36 or 54 mol% chiral units, but not in the film of copolymer containing 78 mol% chiral units. Also, CD values of the copolymeric films decreased with increasing chiral content. After irradiation with linear polarized light at 442 nm, CD values were changed in all the copolymeric films, and the CD values increased with decreasing chiral content in a nonlinear way, while the photoinduced change of chirality of the copolymers increased in a linear way with decreasing chiral content. The results are discussed in terms of interactions between structures and chiroptical properties. Copyright © 2007 Society of Chemical Industry     

Synthesis and phase behavior of cholesteric liquid crystal polymers containing glutamic acid in main‐chain

Four polymers (P₀–P₃) containing peptide chain as polymer backbone were synthesized by condensation reaction with bis(trichloromethyl)carbonate and triethylamine. The chemical structures of the monomers M₀–M₃ were confirmed by FTIR and ¹H‐NMR. The structure–property relationships of the monomers and polymers are discussed. Their phase behavior and optical properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. Monomers M₁–M₃ and polymers P₁–P₃ displayed cholesteric phases. The results demonstrated that the melt temperature and clear point of monomers (M₁–M₃) and polymers (P₁–P₃) decreased with the increase of the flexible spacer length in the side‐chain, and the mesophase temperature range of the polymers increased with the increase of the flexible spacer length. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Preparation of polymer‐dispersed liquid crystal films containing a small amount of liquid crystalline polymer and their properties

Polymer‐dispersed liquid crystal (PDLC) films were synthesized by the copolymerization of liquid crystalline polymer (LCP) precursor, urethane acrylate (UA), and mesogenic monomer (AI) at different conditions. The morphology of polymer matrix changed with the weight ratio of polymer/liquid crystal (LC) ratio and curing temperature, resulting in a large change in the droplet size of LC domains in the PDLC film. The components used in the synthesis of polymer matrix, that is, the weight ratio of LCP, AI, and UA, also strongly influenced the morphology of PDLC films. A small amount of LCP was copolymerized with UA and AI in the preparation of polymer matrix to improve the electrooptical properties such as the viewing angle. Added LCP also affected the morphology and the properties of PDLC. The hydrophobicity of LCP caused changes in the droplet size of LC domain in PDLC films and the anchoring energy between matrix polymer and LC droplets. As the hydrophobicity of the matrix increases, the droplet size of LC domain also increases; on the contrary, anchoring energy decreased, leading to the decrease of driving voltage. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3178–3188, 2000     

Thermal conductivity models for carbon/liquid crystal polymer composites

Thermally conductive resins are needed for bipolar plates in fuel cells. Currently, the materials used for these bipolar plates often contain a single type of graphite in a thermosetting resin. In this study, varying amounts of four different types of polyacrylonitrile carbon fillers (Ketjenblack carbon black, Thermocarb synthetic graphite, Fortafil 243 carbon fiber, and Panex 30 carbon fiber) were added to a thermoplastic matrix (Vectra A950RX Liquid Crystal Polymer), with the resulting resins tested for through‐plane and in‐plane thermal conductivity. There are two unique contributions of this work. The first contribution is the use of the Nielsen model for the through‐plane thermal conductivity as a function of the single filler volume fraction. The model fits the data for all composites well. The second contribution is the development of a new, accurate, empirical model to predict the in‐plane thermal conductivity for all resins containing synthetic graphite or carbon fiber. Both of these models will form the basis for the development of new thermal conductivity models for composites with multiple fillers for fuel cell bipolar plate applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Thermal conductivity of carbon fiber/liquid crystal polymer composites

Thermally conductive resins are needed for bipolar plates in fuel cells. Currently, the materials used for these bipolar plates often contain a single type of graphite in a thermosetting resin. In this study, varying amounts of two different types of polyacrylonitrile based carbon fibers, Fortafil 243 and Panex 30, were added to a thermoplastic matrix (Vectra A950RX Liquid Crystal Polymer). The resulting single filler composites were tested for thermal conductivity and a simple exponential thermal conductivity model was developed for the square root of the product of the in‐plane and through‐plane thermal conductivity . The experiments showed that the through‐plane thermal conductivity was similar for composites up to 40 vol % fiber. However, at higher loadings, the Panex 30 samples exhibited higher thermal conductivity. The experiments also showed that the in‐plane thermal conductivity of composites containing Panex 30 was higher than those containing Fortafil 243 for all volume fractions studied. Finally, the model agreed very well with experimental data covering a large range of filler volume fraction (from 0 to 55 vol % for both single filler systems). The model can be used with existing through‐plane thermal conductivity models to predict in‐plane thermal conductivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5456–5462, 2006     

新型液晶聚氨酯/环氧树脂复合材料的制备及性能

以联苯二酚,2,4-甲苯二异氰酸酯(2,4-TDI),乙二醇,N,N'-二(ω-羟乙基)均苯四甲酰二亚胺(BHDI)为单体,加成反应合成了1种同时含有联苯基和亚胺基的新型液晶聚氨酯(LCPBI),通过IR,DSC、偏光显微镜及X射线衍射仪对其结构和性能进行表征和分析。将该液晶聚氨酯与环氧树脂(E-51)共混制备了液晶聚氨酯/环氧树脂复合材料,通过力学性能测试,热重分析和电镜分析对其性能进行了研究并探讨了其增韧机理。结果表明,加入质量分数为3%的LCPBI,可使复合材料的冲击强度提高2.5倍,拉伸强度和弯曲强度也有不同程度的提高,热分解温度提高15～20℃。     

Preparation and characterization of novel polyimide with chiral side chain for twist nematic liquid crystal display

The synthesis of novel polyimide (PI) films containing chirals in side chain was investigated for utilizing in twist nematic (TN) liquid crystal display (LCD). The polyimide with amine side groups (PI4 a.m.) was prepared by two steps copolymerization of 4,4′‐hexafluoroisopropylidene diphthalic anhydride (6FDA), 4,4′‐oxydianiline (ODA), and 3,3′‐diaminobezidine (4 a.m.) in N‐methyl‐2‐ pyrrolidinone (NMP). In the first step, the oligomer of 6FDA and ODA with mole ratio 4 : 3 was synthesized. In the second step, the oligomer was reacted with 4 a.m. by gradually dropping the oligomer into 4 a.m. solution with the mole ratio 4 : 5. By reacting chiral compounds, mandelic acid, menthyl chloroformate, and menthyl glyoxylate hydrate using condensation reaction with amine groups along polyimide molecules, the novel polyimides can be synthesized. Their chemical structures were confirmed by fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy (¹H‐NMR). The coated glass slides pairs were coated with PI4 a.m. and with each Polyimide/chiral. The liquid crystals (LCs) were inserted between two coated glass slides at above the nematic temperature under the polarized light microscope to observe the alignment of LCs. The results showed the alignment of LCs in some certain direction under Polyimide/chiral pair, regardless of the type of the chiral molecule. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Optical properties of (acetoxypropyl)cellulose mesophases: factors influencing the cholesteric pitch

(Acetoxypropyl)cellulose (APC) forms a thermotropic cholesteric liquid crystalline phase, and with dibutyl phthalate (DBP) it also forms a lyotropic cholesteric phase. The reflection bands for the mesophases occur in the visible region, at wavelengths which depend on concentration and temperatures. The pitch of the cholesteric helicoidal structure is derived from measurements of the mean refractive indices and of the reflection band wavelengths for mesophase samples containing from 0 to 30% diluent at temperatures from ambient to 170°C. The pitch of the thermotropic mesophase increases with increasing temperature and with decreasing molar mass. The pitch of the lyotropic mesophase increases with increasing temperature and diluent content. Pitch values approach infinity at temperatures close to the clearing temperature of the mesophase, and no reversal in the sense of the pitch with temperature or diluent content was detected. The experimentally observed changes in pitch with composition and temperature are in reasonable agreement with the predictions of a recent theory for cholesteric mesophases composed of helical rod-like species. The average distance between chains in the mesophase is estimated from X-ray diffraction measurements, and hence the average angle of twist between neighbouring APC molecules may be found. The angle decreased from 2.2° for pure APC to 0.9° for a volume fraction of 0.73 APC in DBP.     

壳聚糖的制备及其液晶表征

天然高分子材料壳聚糖因其具有抗菌性且具有类似纤维素的性质:可再生、良好的生物相容性、分子具有双螺旋结构、分子结构具有刚性等,且壳聚糖分子还具有良好的抗菌性,其在纺织领域被人们广泛关注。但壳聚糖纤维存在强度不高的缺点,而液晶化合物具有高强度的优点,故对其液晶性的研究日益增多。本文利用浓碱法自制的虾壳壳聚糖在乙酸中液晶临界质量分数仅为1%,并通过偏光显微镜观察到其在酒石酸、丙酸和对甲苯磺酸溶液中显示出典型的胆甾型液晶所具有的指纹状织构,即具有溶致液晶性。壳聚糖在羧酸溶液中随着羧酸的碳链增长,其液晶织构的螺距值亦逐步增大:在甲酸中为13.8~15.5μm,在乙酸中为15.5~17.2μm,在丙酸中增至19.8~22.4μm。     

液晶聚合物调控的蓄热调温材料的储热性能

通过3,3′,4,4′-二苯甲酮四甲酸二酐(BPTCD)与聚乙二醇2000(PEG2000)的酯化反应,制备了具有光热响应的相变聚合物BPTCD-PEG,该聚合物在相变过程中可以形成液晶态.在偏光显微镜下,BPTCD-PEG呈典型的焦锥花形向列相液晶织构.采用DSC对BPTCD-PEG的热性能进行表征,结果表明,BPT...     

Display forming polymer/liquid crystal composite layers and their stability against external mechanical distortions

The liquid crystal display (LCD) technology is confronted with the task to substitute rigid glass plates enclosing the electro‐optically active liquid crystal (LC) material by plastic substrates. In particular, the commercialization of flexible displays requires a sufficient stabilization against external mechanical distortions. To achieve LC layer stabilization, several procedures have been suggested. In this work, the thermal‐induced phase separation (TIPS) technique has been applied to generate composite films consisting of LC compartments which are encased by coherent polymer walls after binodal phase separation. Composite films were prepared from a series of poly(methacrylates) and various commercial nematic LC mixtures. Furthermore, the use of copolymers as well as binary blends from “hard” and “soft” poly(methacrylates) broadens the possibilities to control the film morphology. To compare different polymer/LC composite films regarding their stability under compression load, the samples were investigated by indentation tests using an inverse reflected‐light microscope combined with a digital image acquisition technique. The deformation of the composite layers was evaluated by the uniDAC image analysis which relies on the more general method of Digital Image Correlation (DIC). Some of the fabricated composites show a remarkably high indentation resistance, especially such prepared from poly(1‐tetralyl methacrylate) and poly(4‐tert‐butylcyclohexyl methacrylate). The results facilitate the selection of suitable composite systems for the fabrication of mechanically stabilized flexible LC displays. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrical conductivity model evaluation of carbon fiber filled liquid crystal polymer composites

Electrically conductive resins may have applications as fuel cell bipolar plates. The current trend in this technology is a thermosetting polymer as the matrix containing high concentrations of various types of fillers. These fillers are carbon based and electrically conductive powders, particles, or fibers. In this study, we utilized two composite formulations of polyacrylonitrile fibers (Fortafil 243 and Panex 30) in a liquid crystal polymer (Vectra A950RX) with increasing concentrations. Electrical conductivity tests were performed and modified Mamunya and additive models were applied to the experimental data. These models fit the entire range of data for each composite tested. Four alternate models were also produced: linear, quadratic, exponential, and geometric, with a restricted range of electrical conductivity data greater than 10^?2 S/cm. The exponential and the geometric resulted in the best fits over this restricted data range. These particular models may allow researchers to extrapolate beyond the maximum filler concentrations studied here. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation of liquid crystalline networks doped with azobenzene molecules and their photochemical grating formation behavior

Liquid crystalline (LC) networks with macroscopically uniaxial molecular orientation were prepared by photopolymerization of mixtures of LC mono‐ and diacrylates and a donor–acceptor azobenzene compound in a homogeneous glass cell at the nematic phase, and their photoresponsive properties were investigated. The transparency of the LC networks decreased with a decrease in the crosslinking density with LC diacrylate. The LC networks crosslinked with a few mol percent of LC diacrylate showed an enantiotropic phase transition from an anisotropic phase to an isotropic phase as well as high transparency. Formation and removal of the grating were investigated by irradiating two writing beams with an argon ion laser. Grating less than 1.0 μm could be achieved, and the response time of formation and removal of the grating were in a range of a few tens of microseconds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 943–951, 2003     

Synthesis of a side chain liquid crystalline polycarbonate with a chiral backbone

We report the experimental demonstration of a novel and environmentally benign supercritical carbon dioxide (ScCO₂) technique that yields an optically active, side chain liquid crystalline polycarbonate in a single‐step reaction. The obtained polymer is worthwhile, since it is highly stereoregular and can find applications in an enlarged mesomorphic temperature range compared to its acrylic analogues. The synthesized materials were characterized by IR, ¹H‐NMR, and ¹³C‐NMR, while the thermal properties were measured by DSC. Polarized optical micrograph and wide angle X‐ray diffraction were used for the mesogenic property characterization of the copolymer. The transfer chirality from the backbone to the mesophase is demonstrated on the optical microscopy textures. Being consistent with the ¹³C‐NMR, X‐ray implies an ordered polymeric structure. The DSC analysis of the copolymer indicates that the T_i (the clearing point temperature) value does not change dramatically, whereas a pronounced decrease in T_g (the glass transition temperature) value is observed from that of its acrylic analogues. Hence, the obtained polymer exhibits another practical benefit by widening the mesomorphic temperature range. This study is the insightful combination of material processing and chemical design that elucidates the advantages of ScCO₂ application, in terms of liquid crystallinity and the tacticity of the obtained polymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1915–1921, 2006     

末端叠氮基偶氮苯化合物的制备及液晶性质表征

通过对偶氮苯原料化合物的修饰最终制备得到末端带叠氮基偶氮苯化合物,所得目标产物经1HNMR、13CNMR、FT-IR和元素分析确证化学结构。利用示差扫描量热法(DSC)及偏光显微镜(POM)研究其相转变行为,结果表明,目标产物在升温39.2～69.7℃以及降温65.7～14.3℃范围内具有液晶性质,而4,4’-二(6-叠氮己氧酰基)偶氮苯无液晶性质。     

BODIPY荧光二向性液晶染料的制备及性能

以8-(4-碘苯基)氟硼吡咯为原料,与4-乙炔基苯基胆甾醇酯或4-乙炔基苯戊基双环己基甲醇酯进行Sonogashira偶联反应,制备了两个含氟的荧光二向性液晶染料DC-1和DC-2,其化学结构均由1HNMR、13CNMR和HRMS鉴定。将染料DC-1和DC-2进行光谱测试,最大吸收波长和最大发射波长分别在503和517 nm,发亮绿色荧光。基于宾-主(G-H)效应,将染料DC-1和DC-2作为宾体组分溶于主体液晶E7中,测得DC-2在液晶E7中的吸收二向色比高达8.91,有序参数为0.73,可应用在宾-主型液晶显示器(GH-LCD)中。经差热扫描量热仪(DSC)测试,染料DC-1和DC-2在一定温度范围内具有介晶性质,并通过偏光显微镜(POM)验证了DC-1和DC-2的液晶织构。     

Electrical conductivity and rheology of carbon‐filled liquid crystal polymer composites

One emerging market for electrically conductive resins is for bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases composite electrical conductivity and viscosity. Current technology often adds as much of a single type of carbon filler as possible to achieve the desired conductivity, while still allowing the carbon‐filled thermoplastic matrix material to be extruded and molded into a bipolar plate. In this study, varying amounts of two different types of carbon, one carbon black and one synthetic graphite, were added to Vectra A950RX liquid crystal polymer. The resulting single filler composites were then tested for electrical conductivity and rheological properties. The electrical conductivity followed that typically seen in polymer composites with a percolation threshold at 4 vol % for carbon black and at 15 vol % for synthetic graphite. Over the range of shear rates studied, the viscosity followed a shear‐thinning power law model with power‐law exponent (n ? 1) = ?0.5 for neat Vectra A950RX and (n ? 1) = ?0.7 for highly filled composite materials. Viscosity increased with increasing filler volume fraction for all shear rates. The viscosity–enhancement effect was more rapid for the composites containing carbon black when compared with those containing synthetic graphite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2680–2688, 2006     

FEM calculations of capillary rheometer flow for carbon‐filled liquid crystal polymer composites

There is an emerging market for conductive resins for use in fuel cell bipolar plates. This research focuses on developing a finite element model of a capillary rheometer. Comsol Multiphysics 3.2b was used to model the flow of a remeltable thermoplastic matrix material, Vectra A950RX Liquid Crystal Polymer, with varying amounts of either a carbon black or synthetic graphite filler, to obtain the velocity profile and pressure drop of these composites within the capillary. Previous experimental results have shown that the molten composites obey a shear‐thinning power law behavior. When comparing the model predicted pressure drops from the model with the experimental data, very good agreement was obtained. This signifies that the rheological behavior of the composites can be described by a power law relationship, using parameters specific to each composite. When comparing the modeled velocity profile with the theoretical profile, it was found for all composite formulations that the velocity becomes fully developed within a length of 0.05 times the diameter of the tube, independent of the power law parameters n and m. This work is a necessary first step in developing 2D or 3D mold filling simulations for fuel cell bipolar plate applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

含有偶氮-亚胺基与胆固醇基双液晶基元化合物的合成与表征

合成了一种新型双液晶基元化合物,其含有胆固醇脂液晶基元和偶氮-亚胺连接的三苯环液晶基团,两个液晶基元通过丁二酸脂键相连.对产物的液晶性能进行了表征.该液晶化合物在加热过程(152～305℃)中很宽的温度范围内呈现典型的胆甾相液晶油丝织构,可能被用于信息存储、光转换开关以及非线性光学等领域.