E. B. Barmatov

Influence of silver nanoparticles on the order parameter of liquid crystalline polymers

New polymer nematic nanocomposites are prepared containing 1.43–4.64 wt % of silver nanoparticles whose mean dimensions are 2–4 nm. According to 2H NMR spectroscopic measurements, on increasing the content of metallic nanoparticles, the orientational order parameter Szz of the nematic phase shown by the nanocomposites increases.

Comparative dielectric and TSDC studies of molecular mobility in liquid-crystalline side-chain poly(methacrylate)

Abstract The molecular mobility of a LC side-chain polymethacrylate (PM6) was carried out by dielectric spectroscopy and by thermally stimulated discharge current (TSDC) methods. Six relaxation processes γ2, γ1, β, β1, α, and δ at successively increasing temperatures were observed in PM-6. For each of them, a molecular interpretation was proposed. There is a good correlation between the peak temperature positions obtained from the global TSDC spectrum at an equivalent frequency and those obtained from the dielectric method. The TSDC thermal windowing experiments for PM-6 show the high ability to resolve the overlapping processes at low temperatures. Dielectric and TSDC methods giving different details of the observed relaxation processes, allow us to create the overall picture of molecular mobility in the system under investigation. These two methods revealing the differences and similarities of the obtained results could be considered as complementary to each other.

Preliminary communication Induction of the smectic phase in comb-shaped liquid crystalline ionogenic copolymers by hydrogen bond formation

Using a radical copolymerization of 4-(4-cyanobiphenyl-4-yloxy)butyl acrylate and acrylic acid, a number of new liquid crystalline ionogenic copolymers capable of hydrogen bonding were synthesized. The formation of hydrogen bonds results in an invariant temperature interval of existence for the LC state (up to 52mol% of acrylic acid) and a rather sudden replacement of the nematic phase by the SmA phase with increase in content of acrylic acid (35 mol%) in copolymers.

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.

The effect of silver nanoparticles on the phase state of comb-shaped liquid crystalline polymers with cyanobiphenyl mesogenic groups

A new approach is proposed for the preparation of a new class of hybrid polymer systems based on comb-shaped LC polymers with cyanobiphenyl mesogenic groups and silver nanoparticles with dimensions ranging from 5 to 54 nm. A correlation between copolymer composition and dimensions of the formed nanoparticles is established. As the concentration of nanoparticles in LC copolymer is increased, the resultant glass transition temperature increases, and the temperature interval of the existence of LC phase is reduced. This behavior is related to the adsorption of cyanobiphenyl and carboxylic polymer groups on the surface of silver nanoparticles. In this case, the conductivity and dielectric permittivity of the composites are also increased.

Dielectric spectroscopy and low temperature molecular dynamics of thermotropic side-chain polymethacrylates with side halogen terminal groups

Local forms of molecular mobility of LC side-chain halogen-containing polymers (P-Hal) where Hal is F, CI, Br, or J, with caproyloxyphenyl benzoate mesogenic groups were studied by dielctric relaxtion spectroscopy (DRS) and by thermally stimulated depolarization currents (TSDC) techniques. For all halogen-containing polymers investigated herein three relaxation ranges of dipole polymerization were detected at tempearture below T g , β, γ 1 and γ 2 process in the order of decreasing temperature. The molecular mechanism of these processes correspond to the mesogen motion about the long axis, to the spacer motion, and to the mobility of the mesogen end part, respectively. For all P-Hal, the kinetic characteristics for each of the β, γ 1 and γ 2 processes can be described by a single curve in the Arrhenius plot, log F max = φ(1/T). In other words, the local molecular mobility in the series P-F, P-CI, P-Br, and P-J does not changes with halogen type.

Side group functionalized liquid crystalline polymers and blends VIII. Nematic and SmAre phase formation in hydrogen-bonded blends of smectic side group LC polymers and a low molar mass dopant

Hydrogen-bonded blends based on smectic side group functionalized LC copolymers containing 4-alkyloxybenzoic acid fragments (proton donor) and a non-mesogenic low molecular mass dopant 4-cyanophenyl pyridine-4-carboxylate or 4-methoxyphenyl-d4 pyridine-4-carboxylate (proton acceptor) were obtained. The blends containing 10-35 mol % of low molecular weight dopant form nematic (I-N-SmA) or re-entrant SmA phases (I-SmA-N-SmAre). The temperature dependence of the order parameter S, the birefringence Δn, and the splay K 1 and bend K 3 elastic constants of the nematic phase were studied by 2H NMR spectroscopy and the Fréedericksz method of threshold transitions in a magnetic field. A mechanism for the destruction of the SmA phase and the formation of the nematic phase in the hydrogen-bonded blends is suggested.

Side chain functionalized liquid crystalline polymers and blends, 1. Reentrant nematic phase formation in hydrogen‐bonded blends of liquid crystalline functionalized copolymers with a low molecular weight non‐mesogeic dopant

Hydrogen-bonded blends based on smectic comb-shaped functionalized LC copolymers containing alkyloxy-4-hydroxybenzoic acid fragments (proton donor) and the low molecular weight dopant 4-(4-pyridyloyl)cyanobenzoate (proton acceptor) were obtained. It was observed that blends containing 10–25 mol-% of low molecular weight dopants form a reentrant nematic phase (SmA-RN-SmA-I). The blend behavior in the magnetic field was studied, and the orientational elastic constants of the RN phase were determined.

Side-chain functionalized liquid crystalline polymers and blends, 5. Order parameter for hydrogen-bonded blends of the functionalized liquid crystalline polymer with a low molecular weight dopant

A hydrogen-bonded blend based on comb-shaped functionalized LC copolymers containing alkyloxy-4-hydroxybenzoic acid fragments (proton donor) and a low molecular weight dopant 4-(4-pyridyloyl)methoxybenzoate-d 4 (proton acceptor) was obtained. The temperature dependence of the order parameter S, the birefringence Δn and the bend elastic constant K 3 of the LC copolymer and blend were studied by the 2 H NMR spectorscopy and the Fredericksz method of threshold transitions in a magnetic field. The formation of the blend leads to a decrease of the order parameter S of the functionalized LC copolymer. The essential difference in the order parameter S of the mesogenic groups of the LC copolymers and the dopant molecules was established.

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.