Photoinduced cooperative reorientation in polymer blend films with hydrogen-bonded mesogenic side groups

Thermally enhanced photoinduced cooperative reorientation in hydrogen (H)-bonded polymer blend films was investigated. The films consisted of two kinds polymethacrylates with hexamethylene spacer groups terminated with 4-oxycinnamic acid (P6CA), 4-oxybenzoic acid (P6BA) or 4-(4′-oxyphenyl)benzoic acid (P6PBA) in the side chains. The films were subjected to linearly polarized ultraviolet (LPUV) light and subsequent annealing. Sufficient cooperative in-plane molecular reorientation in P6CA–P6BA blend films was achieved for the first time. In P6CA–P6PBA blend films, however, reorientation was not observed. The molecular weight, as well as the thermal properties of the homopolymers and the degree of photoreaction all played an important role in the cooperative reorientation behavior of the blend films. Finally, uniform alignment control of low-molecular-weight liquid crystals (LCs) on the molecularly reoriented polymer blend films perpendicular to the polarization E of LPUV light was obtained.     

Photoinduced orientation of liquid crystalline copolymer films containing 4-oxybenzoic acid side groups and photo-cross-linkable mesogenic side groups

The cooperative molecular reorientation in methacrylate copolymer films with hexamethylene spacer groups terminated with 4-oxybenzoic acid (BA) and 4-(4-methoxycinnamoyloxy)biphenyl (MCB) in their side chains was investigated by irradiating with linearly polarized ultraviolet light (LPUV) and subsequent annealing. A high degree of cooperative in-plane reorientation of both the BA and MCB groups was obtained when the composition of the BA groups was greater than 50 mol% and hydrogen (H)-bonded LC mesogenic dimers of BA molecules existed. On the other hand, the molecular reorientation was restricted when the BA groups did not form H-bonds. It was clarified that the amount of axis-selectively photoreacted MCB groups and the H-bonds of the BA groups that exhibit a LC nature play important roles in the thermally enhanced molecular reorientation.     

Photoinduced molecular reorientation in photoreactive liquid crystalline copolymers in a phase retarder application

Polymethacrylate copolymers, which have hexamethylene spacer groups terminated with 4-methoxyphenyl-4′-oxycinnamate (MPC) and 4-oxybenzoic acid (BA) in the side chain, were synthesized. Thin films underwent thermally enhanced photoinduced cooperative molecular reorientation using linearly polarized ultraviolet (LPUV) light and subsequent annealing. Moreover, low exposure energy (4-80 mJ cm⁻²) and annealing temperature (<140 °C) provided sufficient cooperative molecular reorientation of both side groups with a large reorientational order (S > 0.5). Tuning the copolymer composition adjusted the birefringence (?n) of homogeneously reoriented films between 0.10 and 0.22 at 517 nm. Finally, a phase retarder (?nd = 130 nm) using an oriented copolymer on a triacetylcellulose (TAC) film substrate, which exhibited a thermal stability up to 140 °C, was fabricated.     

Influence of alkylene spacer length on photoinduced molecular reorientation and LC alignment behavior in photo-cross-linkable liquid crystalline polymeric films with H-bonded cinnamic acid side groups

Photoinduced reorientation of liquid crystalline polymethacrylates comprised of various lengths of alkylene spacers terminated with 4-oxycinnamic acid in the side chain and low-molecular liquid crystal (LC) alignment on the resultant photoreacted films were investigated using linearly polarized UV light. As the length of the spacer increased, the photoinduced optical anisotropy (ΔA) of the thin films increased, and ΔA increased as the irradiating temperature increased. Exposing the polymeric films in the LC temperature range of the material generated an in-plane molecular reorientation because the small photoinduced ΔA was simultaneously amplified. The low-molecular LCs aligned homogeneously on the photoreacted polymeric films, but the LC alignment direction depended on the alkylene spacer length and the degree of the photoreaction.     

Photoinduced optical anisotropy and reorientation in copolymers containing 4-methoxyazobenzene side groups and methyl methacrylate units using linearly polarized 633 nm light

Liquid crystalline (LC) and non-LC copolymers that contain 4-methoxyazobenzene side groups and methyl methacrylate units were synthesized to compare the photoinduced reorientation behavior using the polarization absorption spectra of thin films. Irradiating with non-polarized 365 nm light saturated the Z-isomer in the copolymer films and subsequent exposure to a linearly polarized (LP) 633 nm light generated a photoinduced optical anisotropy (ΔA) for all Z-isomer films based on an axis-selective Z-to-E photoisomerization. When a copolymer did not exhibit a LC nature, ΔA gradually increased until 60-80 mol% of the Z-isomers isomerized to the E-isomers, but decreased upon further photoisomerization reaction. On the other hand, the magnitude of the photoinduced ΔA of a film continuously increased for LC copolymers until E-isomer formation was saturated. Thermal amplification of the photoinduced ΔA was observed for LC copolymers, but the thermal treatment resulted in the disappearance of the photoinduced ΔA for the non-LC copolymers. The axis-selective Z-to-E photoisomerization that preserves the direction of the transition moment of both isomers caused the photoinduced ΔA and increased the liquid crystalline nature of the film during the Z-to-E photoisomerization to induce the self-organization of the mesogenic groups.     

Influence of substituents on the reorientational behavior in photocrosslinkable polymer liquid crystal films with p-substituted cinnamoyloxybiphenyl side groups by irradiating with linearly polarized ultraviolet light and annealing

This paper describes the synthesis and influence of the substituent on the reorientation behavior of photocrosslinkable methacrylate polymer liquid crystals (PPLCs), which contain p-substituted cinnamoyloxybiphenyl (CB) side groups. Irradiating with linearly polarized ultraviolet (LPUV) light induced optical anisotropy of all PPLC films due to an axis-selective photoreaction of the mesogenic groups. The thermally enhanced reorientation direction depended on the substituent groups and liquid crystalline nature of the PPLC. A high in-plane reorientational order (S>0.6) parallel to the polarization of LPUV light was obtained for PPLCs with p-methoxy-CB and p-methyl-CB side groups, while out-of-plane reorientation was predominant for p-fluoro-CB and p-trifluoromethyl-CB side groups.     

Electro-optical properties of the normally transparent type anisotropic polymer dispersed liquid crystal films

We fabricate normally transparent type of polymer dispersed liquid crystal (PDLC) films, which are composed of nematic liquid crystals in anisotropic polymer network. The glass substrates of the films are treated with rubbing such that the polymer and liquid crystal molecules are plane parallel aligned in the sample cell. The liquid crystals used are 5CB and 7CB. The polymer is cured at a variety of UV wavelengths and intensities. The electro-optical properties of these PDLC films are reported. This type of transparent PDLC shows an improvement in the transparency of the clear state and a decrease in the driving voltage.     

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。     

Photoinduced electron transfer in nanostructures of ultrathin polyimide films containing porphyrin moieties

Photoinduced electron transfer between porphyrin moieties and pyromellitimide fragments has been investigated in multi-layered structures of ultrathin polyimide films prepared by the Langmuir-Blodgett (LB) technique. The LB films were composed of three kinds of polyimides, which contained zinc tetraphenylporphyrin (ZnTPP) unit as an electron donor (D-layer), no chromophoric groups (S-layer), and pyromellitimide fragments as an electron acceptor (A-layer). The layered structure and orientational distribution of porphyrin moieties in the LB films were evaluated by surface plasmon measurement and absorption dichroism measurement, respectively. The thickness of monolayer was estimated to be 0.9 nm for the polyamic acid films and 0.4 nm for the polyimide films. The molecular plane of porphyrin moieties was oriented in the direction parallel to the substrate plane. In the multi-layered structures of polyimide LB films, the efficiencies of photoinduced electron transfer from porphyrin moieties to pyromellitimide fragments varied sharply with the number of spacing layers, indicating that the short-range interactions such as electron transfer could be controlled by the fabric of ultrathin films. The rate of electron transfer observed by the fluorescence quenching measurements was numerically simulated for the nanostructure using the Monte Carlo method.     

A comparative study on the thermally enhanced reorientation between random and diblock methacrylate copolymers with photo-cross-linkable mesogenic side groups by irradiating with linearly polarized ultraviolet light

The thermally enhanced photoinduced reorientation behavior of random and diblock copolymer films of methyl methacrylate and methacrylate with a photo-cross-linkable 4-(4-methoxycinnamoyloxy)biphenyl (MCB) side groups was investigated by irradiating with linearly polarized ultraviolet light and subsequently annealing. Random copolymers were synthesized by free radical copolymerization, while diblock ones were obtained by an atom transfer radical polymerization method with a PMMA macroinitiator. The photoinduced optical anisotropy was thermally amplified when the copolymer exhibited a liquid crystalline phase. The random copolymers with a high composition of MCB side groups reverted the orientation direction and inhibited molecular aggregation. For the diblock copolymers, the reorientation behavior was analogous to the methacrylate homopolymer with MCB side groups and transmission electron microscopy revealed a phase separation structure with molecular orientation of the MCB groups.     

Polymer dispersed liquid crystal films for modulating infra-red radiation

The ability of thin films of polymer dispersed liquid crystals to operate as electro-optic devices for modulating infrared radiation between wavelengths of 1 and 5 μm has been investigated. The complex optical properties of the polymer component of the films, and the real component of the refractive indices of the liquid crystals, have been determined using a combination of transmittance spectroscopy and a Kramer's-Krönig dispersion relation utilizing reflectance spectra. The scattering characteristics of single droplets of liquid crystals have been determined and subsequently the contrast ratios of films have been calculated using an anomalous diffraction technique and compared with experimental values. Calculations of film contrast ratios demonstrate good correlation with experimental results for simple film geometries in the absence of multiple scattering. The agreement between experimental and calculated contrast ratios is shown to improve as the light mean free path through the films increases.     

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     

Effects of droplet size on photorefractive properties of polymer dispersed liquid crystals

Effects of liquid-crystal droplet size on orientational photorefractive properties of the polymer dispersed liquid crystals are investigated experimentally. The composites consist of the same chemical components, but the liquid crystal droplet size was varied by controlling the fabrication process. Particular attention is given to the observation and qualitative and/or quantitative modeling of the resolution, dependence of the applied dc field, dynamics of grating generation and photocurrents, which is strongly dependent on the liquid crystal droplet size.     

Effect of polymer structures on electro-optical properties of polymer stabilized liquid crystal films

The polymer stabilized liquid crystal (PSLC) film is a relatively novel electro-optical material, which is generally obtained by dissolving a small amount of a bifunctional photoreactive monomer in a low molecular mass liquid crystal. In this paper, the PSLC films were prepared with photoreactive biphenyl methacrylate monomers by photopolymerization induced phase separation. The effects of liquid crystal concentration, curing time, monomer structures and alignment layer on the electro-optical properties of PSLC films were investigated. The results show that the transmittance in the OFF state (T _OFF) increased with the liquid crystal concentration, but the driving voltage decreased. T _OFF was also influenced by the curing time. Furthermore, when polyimide was used as alignment layer, the films prepared from the bifunctional monomer shows a higher T _OFF, while those from the single functional monomer exhibited a deformed electro-optical curve due to the unsteady polymer networks. __________ Translated from Polymer Materials Science and Engineering, 2008, 24(1): 63–66 [译自: 高分子材料科学与工程]     

聚硅氧烷侧链液晶的研究进展

综述了近年来国内外聚硅氧烷侧链液晶的研究进展，着重介绍了几种主要类型的聚硅氧烷侧链液晶，即近晶型、向列型、胆甾型、偶氦苯型、鱼骨形、光学非线性聚硅氧烷侧链液晶的制备、性能和发展动态，并对其应用前景进行了展望。     

Pattern formation in polymer films under the mask

This paper presents a straightforward method for patterning thin films of polymers, i.e. a prepatterned mask is used to induce self-assembly of polymers and the resulting pattern is the same as the lateral structures in the mask on a submicrometre length scale. The patterns can be formed at above T_g+30 °C in a short time and the external electric field is not crucial. Electrostatic force is assumed to be the driving force for the pattern transfer. Viscous fingering and novel stress-relief lateral morphology induced under the featureless mask are also observed and the formation mechanisms are discussed.     

Annealing of drawn monofilaments of liquid crystalline polymer vectra/vapor grown carbon fiber nanocomposites

The annealing treatment of drawn LCP nanocomposite monofilaments is discussed here. Upon annealing, an unstable structure is generated which presents a strong dependence on the annealing time sequence and temperature as observed by DSC. Moreover, it seems that increasing the draw down of the fiber restricts the formation of this new (unstable) structure. Based on dynamic mechanical analysis and on solid state ¹³C NMR, the nature of the newly-formed structure is elucidated, and based on sequence ordering within the non-oriented amorphous phase in the copolymer, a 10% change in the monomer proportion in the ordered phase is observed after annealing.     

Patterning thin polymer films by surface-directed dewetting and pattern transfer

The pattern evolution processes of thin polystyrene (PS) film on chemically patterned substrates during dewetting have been investigated experimentally. The substrates have patterns of self-assembly monolayers produced by microcontact printing with octadecyltrichlorosilane. Optical microscopy and atomic force microscopy images reveal that ordered micrometer scale pattern can be created by surface direct dewetting. Various pattern sizes and pattern complexities can be achieved by controlling the experimental parameters. The dewetting pattern has been transferred to form PDMS stamp for soft lithography.