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1.
《Liquid crystals》1998,25(3):393-401
For the first time, a series of cholesteric copolymers containing combined chiral photochromic side groups has been synthesized and the phase behaviour and optical properties of the copolymers have been characterized. Specific features of the photochemical and photo-optical behaviour of such systems were studied, and the quantum yields of the photo-induced process in solution and in the condensed state of the cholesteric copolymers were calculated. The selective light reflection wavelength was found to be controlled by the UV radiation. The synthesized polymers were shown to be promising candidates for colour data recording. 相似文献
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Th. Fischer L. Lsker J. Stumpe S.G. Kostromin 《Journal of photochemistry and photobiology. A, Chemistry》1994,80(1-3):453-459
The light-induced modification of the optical properties of photochromic liquid crystalline (side-group) polymers (LCPs) containing azobenzene moieties was studied. Films of such polymers were irradiated with unpolarized and linearly polarized light. Unpolarized irradiation results in a modification of the order parameter, whereas the director orientation remains constant. The light-induced disturbance of the supramolecular order is strongly dependent on the structure of the polymer. A correlation with the enthalpic stability of the liquid crystalline phases is given. Linearly polarized irradiation causes a modification of the order parameter and a reorientation of the side-groups towards a direction perpendicular to the electric vector of the actinic light. This reorientation process is caused by an angular-dependent photoselection within the steady state of the photoisomerization of the azobenzene units. The amount and kinetic of the reorientation differ considerably as a function of certain structural features of the polymers, such as the content of photochromic moieties and the lengths of the spacer chains between the polymeric backbone and the rod-like moieties. It is shown that under certain circumstances the angular-dependent photoselection process may cause a reorientation of the non-photochromic moieties by a cooperative process. The result is a light-induced rotation of the optical axis of the LCP and thus an efficient modification of the birefringent and dichroic properties. This effect can be used in optical data storage. 相似文献
3.
《Supramolecular Science》1998,5(5-6):591-593
Monolayer behaviors for a series of newly synthesized photochromic liquid crystalline copolymers were studied. Results showed that the azo-homopolymer would aggregate heavily after spreading and its monolayer was not suitable for deposition of the reversible photochromic LB film. However, the liquid crystallinity, which resulted by introducing mesogenic cholesteric side chains, could reduce monolayer aggregation and improve reversible photoinduced structural change in LB films. 相似文献
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P. S. Ramanujam Christian Holme Sren Hvilsted Marianne Pedersen Fulvio Andruzzi Massimo Paci Eliana L. Tassi Pierluigi Magagnini Uwe Hoffman Ingo Zebger Heinz W. Siesler 《先进技术聚合物》1996,7(9):768-776
Azobenzene side-chain liquid crystalline polyester structures suitable for permanent optical storage are described. The synthesis and characterization of the polyesters together with differential scanning calorimetry and X-ray investigations are discussed. Optical anisotropic investigations and holographic storage in one particular polyester are described in detail and polarized Fourier transform infrared spectroscopic data complementing the optical data are presented. Optical and atomic force microscope investigations point to a laser-induced aggregation as responsible for permanent optical storage. 相似文献
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Iliopoulos K Krupka O Gindre D Sallé M 《Journal of the American Chemical Society》2010,132(41):14343-14345
A functionalized polymer film allowing for a complete and straightforward second-harmonic generation (SHG)-assisted high-contrast writing-reading-erasing-writing sequence is proposed. The whole process is supported by the reversible photoinduced dimerization of a coumarin chromophore and enables efficient optical data storage that can be detected only by SHG imaging. 相似文献
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The design and preparation of liquid crystalline (LC) block copolymers by use of azo-macroinitiators are outlined. This approach is very versatile and makes it possible to realize diverse architectures of block copolymers, including non-LC/side-chain, non-LC/main-chain and side-chain/main-chain block copolymers. The different blocks were phase separated and underwent their individual phase transitions. In side-chain/main-chain block copolymers different LC mesophases coexisted in equilibrium. 相似文献
9.
Giancarlo Galli 《Macromolecular Symposia》1997,117(1):109-120
Block copolymers and liquid crystals are separately known to order at different length scales. Various types of molecular interactions in liquid crystalline block copolymers determine complex phase behaviors and states of order, and thereby can provide a way of tailoring the material properties. Examples of liquid crystalline block copolymers will be discussed as they may offer unique opportunities for both theoretical and experimental research. 相似文献
10.
C. Noël C. Friedrich V. Leonard P. Le Barny G. Ravaux J. C. Dubois 《Macromolecular Symposia》1989,24(1):283-301
A number of acrylate copolymers having nematogenic groups with ring-X (X = CN, CF3) terminal substituent and highly polarizable groups with ring-NO2 terminal substituent linked to the backbone have been synthesized. The liquid crystalline nature of these copolymers has been established by calorimetric measurements, optical texture observations and X-ray investigations. Ring-CN substituents enhance nematic thermal stability and tend to repress smectic properties while terminal CF3 groups favor smectic A mesophase formation. These copolymers should possess interesting non-linear optical properties. 相似文献
11.
P. Forcén L. Oriol C. Sánchez R. Alcalá S. Hvilsted K. Jankova J. Loos 《Journal of polymer science. Part A, Polymer chemistry》2007,45(10):1899-1910
Diblock copolymers with polymethyl methacrylate and side chain liquid crystalline (LC) azopolymethacrylate blocks were synthesized by atom transfer radical polymerization (ATRP). The azobenzene content in these copolymers ranges from 52 to 7 wt %. For an azo content down to 20% they exhibit a LC behavior similar to that of the azo homopolymers. Thin films of these copolymers were characterized by transmission electron microscopy (TEM). A lamellar nanostructure was observed for azo content down to 20 wt %, while no structure is observed for the copolymer with a 7% azo content. The optical anisotropy induced in these films by illumination with linearly polarized 488 nm light was studied and the results compared with those of the azo homopolymer and of a random copolymer with a similar composition. The formation of azo aggregates inside the azo blocks is strongly reduced in going from the homopolymer to the copolymers. Photoinduced azo orientation perpendicular to the 488 nm light polarization was found in all the polymers. The orientational order parameter is very similar in the homopolymer and in the block copolymers with an azo content down to 20 wt %, while it is much lower in the random copolymer and in the 7 wt %. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1899–1910, 2007 相似文献
12.
Aaron Moment Ruben Miranda Paula T. Hammond 《Macromolecular rapid communications》1998,19(11):573-579
The synthesis of a new liquid crystalline block copolymer consisting of a polystyrene block and a side-chain liquid crystalline siloxane block is reported. The synthetic approach described is based on the anionic polymerization of styrene and cyclic trimethyltrivinyltrisiloxane monomers, followed by functionalization of the siloxane block with side chain mesogens. The siloxane block has a Tg well below 25°C and is designed to exhibit a chiral smectic C* phase at room temperature. These block copolymers are the first side-chain liquid crystalline block copolymers which contain both a high Tg glassy block and a low Tg liquid crystalline block. 相似文献
13.
Balamurugan Subramanian Asiqur Rahman Norbani Abdullah Vijay Srinivasan Murugesan Suresh Dhandapani 《Liquid crystals》2016,43(12):1791-1803
Linear main-chain polymers (P1, P2 and P3) have been synthesised and characterised. The polymers were designed to understand the rigidity of the mesogen’s linking groups and its effect on transition temperature. The liquid crystalline behaviour of these polymers was investigated using polarised optical microscopy and differential scanning calorimetry. All polymers exhibited phase transition on heating and cooling runs. The mesophase stability decreases with the decrease of rigidity of the second mesogen (P2>P1>P3). Similarly, the enthalpy and entropy changes are dependent on the rigidity of the second mesogen (Mesogen B). Polymer P1 undergoes photoisomerisation under UV-visible light irradiation and it attains a photo-stationary state at 275 s. This provides an opportunity to investigate the third-order non-linear optical properties. The non-linear behaviour of polymer P1 in chloroform presents a distinct deviation in a different concentration, where polymer P1 also exhibits a negative non-linear refractive index. Thus, polymer P1 can be used as a potential candidate for optical device applications such as optical limiters. 相似文献
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A composite material based on a liquid-crystalline gel has been prepared via the polymerization of diphenylolpropane dimethacrylate in the presence of the commercial nematic liquid crystal LC-1277 (94.3 wt %). Polymerization is performed under the action of UV irradiation. In the presence of the applied electric voltage, light scattering and birefringence of the samples are changed. The critical field of the electrooptical effect is found to be 2 V, the turn-on time of the effect is 9 ms (this time decreases with increasing voltage), and the turnoff time is 6 ms (independent of voltage). This material can be used in devices for optical irradiation control. 相似文献
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Polymers possess great significance in data storage technology. Taking as an example electrical and optical data storage, the state of development, properties required and opportunities for application of selected polymers are discussed, namely: (i) ferroelectric polymers with low switching voltages and extremely short switching times for electric data storage; and (ii) transparent polymers with low birefringence and high thermal stability for optical data storage. In the area of electrical data storage devices/memories, ferroelectric polymers have not been able to establish themselves up to now due to their long switching time and limited thermal stability. However, recent investigations show that suitable copolymers based on PVDF/TrFE copolymers in ultra-thin layers can achieve switching times of ≤100 ns. Nevertheless, the limited thermal stability of PVDF/TrFE copolymers prevent them from being integrated into the usual manufacturing process for Si-based data storage devices (D-RAM resp. S-RAM) and thereby frustrates the desired objective of producing nonvolatile random access memories (NV-RAMs). In the area of optical data storage technology, polycarbonate (PC) has established itself due to its favorable combination of properties. Thus, audio compact disks (CDs) are manufactured exclusively of PC, while high-flow PC types of high optical purity are clearly the preferred substrate material for optical data storage disks. The increasingly stringent requirements to be met in terms of lower birefringence and better thermal stability mean that the development of suitable modified or substituted polycarbonates is required. The development work being carried out worldwide in this area is reviewed here, and new suitable substituted polycarbonates with lower birefringence and significantly increased thermal stability up to glass temperatures of 238°C are presented. In addition, we deduce structure—property relationships for the above-mentioned structurally modified polycarbonates, specifically considering rotation potentials along the polymer backbone. 相似文献
16.
Jui‐Hsiang Liu Po‐Chih Yang Yi‐Hong Chiu Yasuo Suda 《Journal of polymer science. Part A, Polymer chemistry》2007,45(10):2026-2037
To overcome the defects of the thermal instability of azobenzene, a series of novel photochromic, chiral, liquid‐crystalline monomers and polymers were synthesized from (+)‐camphor. The copolymerization of the photochromic monomers with comonomers was carried out. The synthesized monomers and polymers were identified with nuclear magnetic resonance, Fourier transform infrared, and elemental analysis. The composition of the copolymers was estimated with elemental analysis. The specific rotation of the chiral compounds and polymers was evaluated. The thermal stability and phases of the polymers during heating and cooling cycles were studied with differential scanning calorimetry and thermogravimetric analysis. The phases of the polymers were identified with polarized optical microscopy textures and X‐ray diffraction analysis. The distance between the layers of smectic liquid crystals was estimated from the diffraction angles. Photoisomerization of the configurational E/Z structures was investigated with an ultraviolet–visible spectrophotometer with 300‐nm ultraviolet irradiation. The thermal stability of the Z‐structural segment in the polymers was confirmed through the heating of the polymer at 70 °C for over 10 h. The photoisomerization and thermal stability of the C?C bond in the polymeric materials were demonstrated through a series of novel chiral polymers synthesized in this investigation. Both the polarity of the center part and the molecular length at the ends of the molecules were found to be necessary factors for the formation of liquid‐crystalline molecules. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2026–2037, 2007 相似文献
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A series of four block copolymers based on aromatic acetoxy-polysulphone (Ac-PSF), terephthalic acid (TPA), m-phthalic acid (MPA), acetoxy-benzoic acid (Ac-HBA), and a di(acetoxy)bisphenol monomer were synthesized. Their structures were determined by IR, thermal mechanical analyses and solubility tests. They all exhibit liquid crystalline behaviour. 相似文献
18.
Hideshi Hattori Toshiyuki Uryu 《Journal of polymer science. Part A, Polymer chemistry》2000,38(5):887-894
Photochromic liquid‐crystalline copolymers consisting of a photochromic monomeric unit containing both a spironaphthoxazine group and an undecamethylene spacer, and a liquid‐crystalline monomeric unit containing both a cholesteryl group and a decamethylene spacer were prepared to investigate the effect of the thermal properties of the photochromic monomeric unit on the mesomorphic order of the side chain of the related copolymers. The photochromic liquid‐crystalline copolymers containing a photochromic liquid‐crystalline monomeric unit showed only a smectic phase. On the other hand, the photochromic liquid‐crystalline copolymers containing a photochromic non‐liquid‐crystalline monomeric unit showed a chiral nematic phase (cholesteric phase). The photochromic chiral nematic liquid‐crystalline copolymer containing 14 mol % photochromic monomeric unit reflected visible light around 104 °C. To lower the temperature range of reflection of visible light, cholesteryl oleyl carbonate was used as a chiral nematic plasticizer for the photochromic chiral liquid‐crystalline polymer systems. Photo‐induced pitch change of the mixture by means of UV irradiation was investigated and it was concluded that the pitch change observed under UV irradiation was mainly induced by thermal effect in the case of our system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 887–894, 2000 相似文献
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Liquid crystals for holographic optical data storage 总被引:1,自引:0,他引:1
A tutorial review is presented to inform and inspire the reader to develop and integrate strong scientific links between liquid crystals and holographic data storage, from a materials scientist's viewpoint. The principle of holographic data storage as a means of providing a solution to the information storage demands of the 21st century is detailed. Holography is a small subset of the much larger field of optical data storage and similarly, the diversity of materials used for optical data storage is enormous. The theory of polarisation holography which produces holograms of constant intensity, is discussed. Polymeric liquid crystals play an important role in the development of materials for holographic storage and photoresponsive materials based on azobenzene are targeted for discussion due to their ease of photo-reversion between trans- and cis-states. Although the final polymer may not be liquid crystalline, irradiation can induce ordered domains. The mesogens act in a co-operative manner, enhancing refractive indices and birefringences. Surface relief gratings are discussed as a consequence of holographic storage. Cholesteric polymers comprising azobenzene are briefly highlighted. Irradiation causing cis-trans-isomerisation can be used to control helix pitch. A brief mention of liquid crystals is also made since these materials may be of future interest since they are optically transparent and amenable to photo-induced anisotropy. 相似文献