Photochromic chiral liquid crystalline systems containing spiro-oxazine with a chiral substituent I. Synthesis and characterization of compounds

Photochromic acrylates containing both biphenylene and spiro-oxazine moieties with a chiral substituent and the related polymers were prepared and yielded photochromic chiral liquid crystalline systems. The photochromic acrylates containing both an undecamethylene group and a (2S, 3S)-2-chloro-3-methylpentanoyloxy group (A11SOP) or a (-)-menthoxyacetoxy group (A11SOM) gave a supercooled mesophase; the latter reflected right-handed visible light (blue colour) at room temperature. On the other hand, the photochromic acrylate containing both the (R)-(-)-2-methylpropylene and (2S, 3S)-2-chloro-3-methylpentanoyloxy groups (A3SOP) showed no mesophase. The related homopolymers, PA11SOP and PA11SOM, did not exhibit mesophases because of steric hindrance between the side groups of the polymers. However, only PA11SOM exhibited shear-induced birefringence under 100-104°C. Several copolymers consisting of the nematogenic monomer, 4-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzonitrile (A6CN), and A11SOP or A11SOM possessed a smectic phase due to reduction of the steric hindrance between the potentially smectogenic A11SOP or A11SOM moieties.     

BIOLOGICALLY DERIVED PHOTOACTIVE MACROMOLECULAR AZODYES

Azophenols with various substituents at the para position of the phenyl ring were enzymatically polymerized in the presence of H₂O₂. Structural characterization of the synthesized polymers by FTIR, FT-Raman, and NMR (¹H and ¹³C) spectroscopy confirms our previous observation that this enzymatically catalyzed coupling reaction occurs primarily at the ortho positions, with some substitution at the meta position of the phenol ring. The strong constraint and poor packing of the azobenzene chromophores in the polymer leads to a significant blue shift of the π-π^* transition absorption and slow photoisomerization and thermal relaxation in comparison to the monomers. Surface relief gratings (SRG) with large surface modulation have been fabricated on these enzymatically synthesized polymer films.

     

APplication of Continuous Thermodynamics to the Stability of Polymer Systems. II

A determinant criterion for the critical state in solutions and mixtures of polydisperse polymers is established within the general framework of Gibbs theory. The treatment continues an earlier paper by considering more general Gibbs free energy relations: The function replacing the x-term in the classic Flory-Huggins equation is permitted to depend on a finite number of moments of the polymer distribution(s) so as to embrace most Gibbs free energy relations of practical use. The new criterion leads to a very large reduction of computer time and of needed storage capacity compared to the traditional Gibbs determinant criterion. Some relations known from the literature are shown to be special cases of the established new criterion.     

Dynamics of phase transitions in a liquid crystal probed by Raman spectroscopy

Raman spectra of the Schiff 's base liquid crystalline compound 5O5, N-(4- n-pentyloxybenzylidene)-4'-n-pentylaniline, have been recorded as a function of temperature from 22 to 80°C in the 1140-1220 cm^-1 and 1550-1640 cm^-1 spectral regions. From careful deconvolution of the spectral features using Lorentzian profiles, precise values of peak positions, integrated intensities and linewidths of some selected Raman bands were obtained. The variations of the Raman spectral parameters with temperature are discussed in terms of changes in the molecular alignment and its effect on intra-/inter-molecular interactions at the Cr-G, G-SmF, SmF-SmC and SmA-N phase transitions. From a detailed study, it is inferred that the increased orientational/vibrational freedom of the alkyl chains, as well as the delocalization of the electron clouds, is responsible for the spectral anomalies at the Cr-G transition. Loss of positional ordering and twist around the -C₆H₄-N= bond takes place at the SmF-SmC transition. In the SmA-N transition, some evidence for the formation of cybotactic clusters was obtained.     

Synthesis of novel β2,2-amino acid from D-mannose and attempted synthesis of peptides from the amino acid

The study describes the synthesis of new α,α-disubstituted β-amino acid (β^2,2-Caa) and attempts the synthesis of peptides from it. The β^2,2-Caa was prepared from D-(+)-mannose, using crossed aldol and Cannizzaro reactions.     

Polymer network liquid crystal grating/Fresnel lens fabricated by holography

In this article, polymer network liquid crystal (PNLC) grating/Fresnel lens is fabricated by holography. The exposure light pattern for the grating is obtained by interfering two planar wave fronts, while the Fresnel pattern is achieved by interfering a planar wave front and a spherical wave front. Owing to the alignment effect and anchoring power of polymer network, the holographic PNLC grating achieves improved diffraction efficiency, and remarkably reduced operation voltage (reduced by 80%) compared with holographic polymer-dispersed-liquid-crystal and holographic polymer-stabilised blue-phase liquid-crystal gratings, while maintaining submillisecond response. Moreover, it achieves high spatial frequency with a 2-μm grating period, thanks to the holographic fabrication. The holographic PNLC Fresnel lens also exhibits attractive electro-optical properties.     

Wide-viewing-angle switchable image splitter obtained using varied-line-spacing H-PDLC Bragg grating

We propose the use of a varied-line-spacing (VLS) holographic polymer-dispersed liquid crystal (H-PDLC) Bragg grating as a switchable image splitter to generate a compatible three-dimensional (3D) stereogram and to increase the viewing angle of the observer. To fabricate the VLS grating, a cylindrical lens is adopted to form a cylindrical wave, which interferes with a plane wave, generating an H-PDLC grating with a continuously varying period. The proposed holographic optical element (HOE)-based image splitter comprises two VLS H-PDLC gratings. It can be attached on a designed pattern, with two rectangles taking the place of conventional liquid crystal display panel pixels, and can separate them into right and left viewing fields with a wider range. Experimental results show that the movement of the eyes of the observer can reach 37.6 mm. A theoretical simulation indicates that a shorter focal length of the cylindrical lens can yield a larger movement range. Switching between two-dimensional and 3D modes can be performed by applying an external alternating-current voltage at ~80 V. The contrast ratio of the diffracted images induced by crosstalk is greater than 60%, which indicates the feasibility of the proposed HOE for 3D image splitting.     

Constructing the Co cyclic Structures for Crossed Copro duct Coalgebras

In this paper, we construct a cocylindrical object associated to two coal-gebras and a cotwisted map. It is shown that there exists an isomorphism between the cocyclic object of the crossed coproduct c...     

Similarity degrees for the crossed product of von Neumann algebras

In this paper, we will estimate an upper bound for the similarity degree of the crossed product of a hyperfinite finite von Neumann algebra by weakly compact action of an infinite discrete group. We will also improve some upper bounds for similarity degrees of some finite von Neumann algebras.     

The real rank zero property of crossed product

Let be a unital -algebra, and let be a -dynamical system with abelian and discrete. In this paper, we introduce the continuous affine map from the trace state space of the crossed product to the -invariant trace state space of . If is of real rank zero and is connected, we have proved that is homeomorphic. Conversely, if is homeomorphic, we also get some properties and real rank zero characterization of . In particular, in that case, is of real rank zero if and only if each unitary element in with the form can be approximated by the unitary elements in with finite spectrum, where , , and if moreover is a unital inductive limit of the direct sums of non-elementary simple -algebras of real rank zero, then the above can be cancelled.