J. C. Dubois

Some Novel Smectic* Liquid-Crystalline Side-Chain Polymers

Abstract Three acrylate side-chain polymers in which the mesogenic moieties are based on the 4-n-alkoxyphenyl-4′-(4″-methylhexyloxy) benzoates have been characterized by differential scanning calorimetry, optical microscopy and X-ray diffraction. For shorter flexible spacers (n = 2) both smectic A and C* phases are observed thus making this polymer interesting for the fabrication of electro-optical devices based on ferroelectric properties (a smectic A phase is required for alignment purposes). For longer flexible spacers, (n = 6, 11) only the smectic A phase remains.

Liquid Crystalline Side Chain Polymers Derived From Poly-acrylate, Poly-methyacrylate and Poly-α-chloroacrylate

Abstract Interest in liquid crystalline side-chain polymers has grown tremendously in recent years because of their theoretical aspects and their potential applications. Over the past few years, a considerable research effort has been made in electro-optic display using nematic or smectic. A mesogenic side-chain polymers. On the other hand, non linear optical effects have been obtained with a nematic side-chain copolymer doped with a molecule exhibiting an extremely large molecular hyperpolarizability β and poled with a D.C. electricfield.

Orientation of Discotic Mesophases

Abstract The orientation of some fluid (DF) and optically uniaxial columnar (D) discophases by surfaces is examined by optical microscopy. The test materials are 2,3,6,7,10,11 hexa-substituted triphenylenes, including two new compounds exhibiting mesophases at room temperature, and a binary mixture with a DF, phase stable between 57 and 100°C. The alignment with the directors perpendicular to the walls can be obtained on glass surfaces coated with flat molecules possessing six polar side-functions. Similar homeotropic alignments for the DF phase and total normal orientations for the D phase are observed on faces of cleaved apophyllite and muscovite crystals. For the DF phase, the uniform alignment with the directors parallel to the surfaces is obtained using glass surfaces coated with silicon oxides deposited at oblique incidence. Mutual orientations of the D and DF phases are noted. Between two slides and with the parallel alignment, left or right handed twisted fluid discophases with only an infinite-fo...

Dielectric relaxation and molecular motion in comb-shaped liquid crystal polymers

Abstract Dielectric studies have been performed on a series of oriented polyacrylates in broad frequency and temperature ranges, 5 Hz to 1 GHz and – 170°C, to + 200°C respectively. In order to assist in the identification of the observed relaxation mechanisms, different molecular structures of the mesogenic pendant group connected to the main chain via a variable intermediate group have been investigated. The influence of the intermediate group (spacer length n), of the central group (O or COO), of the interphenyl group (COO) as well as that of the terminal group (CN or OCH3), upon the nature of the relaxations (α, β, γ or ω) and the critical times of the molecular dynamics in side-chain liquid crystal polymers are discussed separately.

Synthesis and Properties of Smeclic Side-Chain Polymers

Abstract In the chiral smectic phase (i.e. the C phase), the molecules are arranged randomly in layers and tilted with respect to the normal layer. The symmetry plane of the ordinary smectic C structure is absent because the molecules are chiral. The only symmetry element is a twofold rotation axis which allows molecules to “flip-flop” head-to-tail. If there is any transverse electric molecular dipole moment, its component along this axis cannot be averaged to zero and so each Layer is spontaneously polarized. However, on passing from layer to layer the tilt direction of the molecules is turned through a small angle about an axis perpendicular to the layers and hence a helical structure is formed. The spontaneous polarization is rotated from one layer to the next about the helical axis and averages to zero in a bulk sample. Hence, the chiral smectic phase is ferroelectric only if the helical arrangement is suppressed.

Mesomorphic Properties of Some New Flurinated Liquid Crystals: the 4-n-Alkoxyperfluorobenzoate Series and Trifluoromethylbiphenyl Dervatives

Abstract We describe here the synthesis, the mesomorphic and the dielectric properties of two families of flurinated compounds: the 4-alkoxyperflurobenzoic acid 4′hydroxy-4-cyanobiphenyl esters and the 4-trifluroromethyl-4′ substituted biphenyl derivates. Some compounds exhibit only a wide temperature nematic range, while others have a wide temperature smectic A range with or without a nematic mesophase. These compounds are possible additives to mixtures of interest for displays.

Synthesis and Mesomorphysm of Some New Ferro-Electric Smectic Liquid Crystals

Abstract In this work, compounds having the general formula: with (X = H, Br, CN, Cl) and (R1 (or/and) R2 = 3-methylhexyl or 2-methyl-butyl, n-alkyl were prepared and their phase transition temperatures and mesomorphic properties determined.

Properties of side chain liquid crystal and amorphous polymers. Applications to non-linear optics

Abstract Comb-like liquid-crystalline polymers exhibit many unique properties that challenge not only basic research but also numerous technological opportunities. They combine (partly) the properties of orientation of low molecular weight liquid crystals with the rigidity of polymers. For example, they can be oriented in the mesomorphic state and the structure frozen in a glassy state. These polymers with functionalized pendent groups lead to potential applications in the field of nonlinear optics, or in the domain of electro-optical displays. Other polymers like polysilanes show interesting properties such as photo-conductivity. This paper describes the properties and applications of some new side chain liquid-crystalline polyacrylates and their amorphous copolymers. It also describes the photo-conductive properties of polysilanes and their applications in spatial light modulators with liquid crystals. In the first part of this paper, we describe the properties of liquid crystal copolymers and amorphous...

Second Harmonic Generation In Amorphous Polymers

The poling process of polymers doped with chromophors is of great importance for the non linear properties of these materials. So, after having optimized the poling conditions (Ep, Tp), the non linear optical coefficients d33 have been measured for PMMA doped with different percentages of azo dye. We have also synthetized new copolymers in which the dye is linked to the backbone, investigated their behaviour and compared them to the guest host systems.

Some New Side-Chain Liquid Crystalline Polymers For Non Linear Optics

Two different ways have been investigated to obtain side-chain liquid crystalline polymers suitable for second harmonic generation (SHG). The aim of the first one was to obtain host nematic comb-like homopolymers having a small degree of polar association of their side chains, by using a 3-fluoro-4-cyanophenyl benzoate end group. The second way consisted in synthesizing liquid crystalline polymeric systems where a mesogenic monomer and a monomeric molecule bearing a group exhibiting a large molecular hyperpolarizability p , were copolymerized. In this paper, we report on the synthesis and the phase behaviour of these two families of polymers.