E. L. Tassi

Side-chain liquid crystalline polyesters for optical information storage†

We report erasable holographic recording with a resolution of at least 2500 lines/mm on unoriented films of sidechain liquid-crystalline polyesters. Recording energies of approximately 1 J/cm(2) have been used. We have obtained a diffraction efficiency of approximately 30% with polarization recording of holograms. The holograms can be erased by heating them to approximately 80 degrees C for approximately 2 min and are available for rerecording.

Calorimetric Study of the Polymorphism of a Novel Polyester Containing Cyanoazobenzene Side Groups

Abstract The phase behavior of a novel comb-shaped polyester (P8a12), synthesized from 2-[8-(4-(4-cyanophenylazo)-phenoxy)-octyl]-1,3-propanediol and tetradecanedioic acid, has becn studied by differential scanning calorimetry. It has been shown that the phase behavior of this polymer is strongly dependent of the thermal history. Up to four, partially overlapped endothermic effects have been found in the DSC heating scans, whose relative intensities markedly change with the conditions of the previous thermal treatment, as well as with the scanning rate. These effects have been tentatively associated with the transitions of as many different polymer structures. The thermal treatments needed for selectively developing the different structures in P8a12 specimens have been determined. The structures have been preliminarily studied by X-ray diffraction and optical microscopy.

IR dichroism study of orientational ordering of liquid-crystalline acrylates

Orientational ordering of four liquid-crystalline acrylates induced by the surface of KBr plates over a wide temperature range was studied by the IR dichroism technique. IR spectra of homogeneously aligned samples were used to calculate the angles between the direction of the transition moment for a series of vibrations of the mesogenic fragment and its long axis. A method for calculation of the homeotropic orientation parameter of molecules was proposed. The orientation parameters of homogeneously and homeotropically aligned samples in the nematic, smectic (A), and chiral smectic (I andH) phases were calculated. Thein situ photopolymerization of acrylates in the smectic phases occurs with retention of the orientational ordering in the polymer films formed.

A New Chiral LC Acrylate that Exhibits Pyroelectricity

Abstract The new material (R)-4-(5-acryloyloxy-4-methylpentanoyloxy)-4′-octanoyloxy biphenyl has been synthesised and characterised by POM, DSC, X-ray diffraction, IR dichroism, pyro- and piezoelectric techniques. The acrylate was shown to exhibit direct isotropic to smectic H* phase transition. The natural texture of the H* phase separates from the isotropic phase in the form of bâtonnets and rounded domains, the latter develop into a mosaic. The mesophase was found to align in a thin cell of KBr plates with homeotropic anchoring independently of the type of surface treatment. The molecular organisation in the H* phase strongly favours fast and efficient polymerisation when the initial orientation retains upon the reaction. The structure of the crystal and H* phases is mono-layer, the molecules pack monoclinic in antiparallel fashion with long-range polar ordering. The pyroelectric coefficient was found to be very high in the crystal (γ = 2.0÷2.9 nC/cm2·K) and H* (γ = 2.9÷1.0 nC/cm2·K) phases. The direct...

Orientation behavior and in-situ photopolymerization of two mesogenic acrylates

IR spectroscopy was used to analyze the orientation behavior and in-situ photopolymerization of two mesogenic acrylates in the chiral smectic I phase and in the SA phase, respectively. The orientation parameter, S, was determined using unpolarized radiation and by comparing the spectra of the mesophase with those of the isotropic phase. The type of alignment was deduced from the observation that the absorption is higher in the mesophase than in the isotopic phase for vibrations perpendicular to the mesogenic core. The change in the relative intensity of the bands with opposite direction of transition moments showed that the long axis of the mesogenic cores is tilted from the direction of the incident beam.

Effect of the composition on the structure and ferroelectric properties of side chain liquid crystalline copolyacrylates

Abstract The structure and physical properties of two side chain liquid crystalline polyacrylates are discussed, one bearing biphenyl core and chiral carbon atom in the flexible spacer, and the other a phenyl benzoate core. The biphenyl version displays two smectic phases of S*F and S*F types and no ferroelectric switching. The phenyl benzoate variant displays a single SC phase. The copolymerisation of the two monomers led to polymeric materials exhibiting a S*c polymorphism and composition dependent structural features. Only the copolymer of equimolar composition displayed a strong piezoelectric response in the S*F phase and ferroelectric behaviour in the lower temperature S*c modification.