Influence of the Molecular Structure of Comb-Shaped Photochromic Copolymers on Photoinduced Birefringence

A series of mesomorphic and amorphous photochromic copolymers containing azobenzene groups were prepared. The emergence of induced birefringence in films of these copolymers under the action of plane-polarized laser light was studied.     

Side‐chain functionalized liquid crystalline polymers and blends, 6. Phase behavior,structure and magnetic properties of Cu(II) containing liquid crystalline ionomers

The new series of the LC ionomers containing copper ions has been obtained and their phase behavior has been studied. It was shown that at low metal ion concentrations in the LC ionomers (˜2 mol‐%) the induction of the SmA phase is observed. An increase in the copper ion concentration is accompanied by a slight rise in clearing and glass transition temperatures. The magnetic properties of LC ionomers were studied at the first time. It was shown that LC ionomers are antiferromagneties with a strong exchange interaction J = 174–178 cm^–1. Temperature dependencies of the magnetic moment and the magnetic anisotropy are adequately described in the framework of the 1‐D‐Heisenberg linear‐chain model.     

Induction of the chiral nematic phase in hydrogen-bonded blends of smectic copolymers and low molar mass dopant

A new approach for the preparation of chiral nematic materials is described. The induction of a chiral nematic phase in hydrogen-bonded blends of smectic comb-shaped LC copolymers containing alkyloxy-4-oxybenzoic acid fragments with a low molar mass chiral dopant (a derivative of pyridine) was observed.     

Optical isotropic mesophase in side chain copolymers containing isophthalic acid groups

Random side chain copolymers, containing cyanobiphenyl mesogenic units and 37-58 mol % of isophthalic acid monomer units, possess an unusual ability to produce optically isotropic mesophases. This is demonstrated by the absence of birefringence and by high optical transparency of their films. At the same time, corresponding DSC curves show a well pronounced first order transition with a heat of fusion of 1.5-2.34 kJ mol^-1. A key reason behind the formation of an optically isotropic mesophase is likely to be related to the microphase separation between side groups of the copolymers.     

Optically isotropic mesophase in comb-shaped copolymers with side mesogenic groups

Two series of comb-shaped copolymers poly(4-(4-cyanobiphenyl-4′-yloxy)butyl acrylate)-co-(4-(6-acryloyloxyhexyl-1-oxy)isophthalic acid)) and poly(4-(6-acryloyloxyhexyl-1-oxy)benzoic acid)-co-(acrylic acid)) have been prepared by free-radical copolymerization, and their phase diagrams have been constructed. Formation of the optically isotropic phase characterized by the absence of birefringence and high optical activity has been demonstrated for a number of copolymers. At the same time, the DSC curves of these compounds show a well-defined phase transition with the heat of melting equal to 2–5 J/g. Specific features of hydrogen bonding in the copolymers have been studied by IR spectroscopy. It has been speculated that there is correlation between microphase separation between hydrophobic and hydrophilic units in the copolymers and formation of the optically isotropic mesophase.     

Side group functionalized liquid crystalline polymers and blends VII. Phase behaviour and elastic constants K1 and K3 for hydrogen bonded blends of a functionalized LC copolymer with a low molecular mass non-mesogenic dopant

New hydrogen bonded blends of LC copolymers containing functional carboxyl groups with a low molecular mass pyridine-containing dopant were obtained and the orientational, optical and elastic properties of the blends were measured using the Fréedericksz method of threshold transitions in a magnetic field. The averaged order parameter S of the hydrogen bonded blends is found to be lower than that of the initial functionalized LC polymers. Furthermore, a considerable increase in the K₃/K₁ ratio is observed caused by an increment in the average 'effective' length of the hydrogen bonded mesogenic group. For the first time it is proven that LC blends with hydrogen bonded mesogenic groups obey the same main relationship of orientational elastic deformations as common nematic LC polymers with covalent bonding of mesogenic side groups.     

New polymer liquid-crystalline CdS nanocomposites forming a chiral nematic phase

A new approach has been developed for the design of liquid-crystalline polymer nanocomposites combining the unique properties of polymer cholesterics and quantum dots of CdS.     

Influence of silver nanoparticles on the phase behavior of side-chain liquid crystalline polymers

The synthetic approach to the new class of mesomorphous nanocomposite polymer systems was developed. It is based on the in situ reduction of silver ions in the liquid crystalline (LC) polymer matrix leading to the formation of nanoparticles with typical sizes in the range of 5-30 nm. The influence of silver nanoparticles on the phase state of the LC composites, i.e., type and temperature interval of the mesophase, was studied. Regardless of chemical structure of the LC polymer matrix, an increase in the metal concentration is accompanied by a decrease of clearing temperature due to adsorption of macromolecules on the nanoparticle's surface. In the case of an LC copolymer with cyanobiphenyl side mesogenic fragments, the complete disruption of mesophase is observed below 2 wt% content of silver. This phenomenon is, most likely, a result of chemosorption of terminal cyano groups on the nanoparticles with the formation of sigma complexes that disturb packing of the mesogenic units.