Wieslaw Pyzuk

Nonlinear dielectric effect near the critical point of binary mixtures

Abstract The nonlinear dielectric effect (NDE) was measured in two binary systems near the critical point. The effect of independent of specific dipole-dipole interactions in contrast with previous conceptions. Its singular part is proportional to ( T − T c ) − 1 2 in agreement with Sniders theory as applied to NDE.

Enaminoketones as calamitic liquid crystals with a novel hydrogen-bonded rigid core

Abstract A series of compounds having an aminopropenone-3 group between two aromatic rings has been synthesized and thermally stable enantiotropic mesogens with properties typical of three ring liquid crystals were obtained. The mesomorphic properties of the molecules result from the presence of a rigid calamitic core stabilized by a hydrogen-bonded cis-s-cis quasi-ring form of the enaminoketone group.

Pretransitional nonlinear dielectric effect, Kerr effect and optical rotation in isotropic cholesterogens

Abstract Cholesteryl oleate and cholesteryl oleyl carbonate have been studied in the vicinity of the isotropic-blue phase transition by nonlinear dielectric effect (NDE), electro-optical Kerr effect (EKE) and optical rotation (OR) methods. The electrically induced pretransitional effects follow the classical 1/(T-T*) behaviour, the OR reveals more complex behaviour. The noncritical background due to contributions from individual molecules, is observed by the NDE method. The electric permittivity anisotropies of the perfectly ordered phase are determined from the ratio of the NDE to EKE amplitudes. Some procedures which yield the accurate determination of the Kerr constant in chiral systems are discussed.

Smectic polymorphism in a series of three-ring enaminoketone compounds

Abstract Liquid crystalline properties of 1 - (4′ - alkoxyphenylamino) - 3 - (4′ - hexyloxyphenyl)-prop-1-en-3-ones, from methoxy to heptadecyloxy, have been examined by optical, DSC, and X-ray methods. The phase diagram for the series exhibits a rich polymorphism of tilted smectic phases, for example, five mesophases were found for the hexyloxy derivative. A characteristic feature of the phase diagram is a gap in the crystal G phase area. For the heptyloxy homologue, a direct crystal H-smectic F phase transition was found; in the case of shorter as well as longer terminal substituents, the phase sequence crystal H–crystal G–smectic F is observed. Calorimetric and X-ray studies revealed the existence of a tricritical point on the crystal G–smectic F transition line.

Kerr effect in the critical solutions of propionitrile

Abstract The electrooptical Kerr effect (EKE) has been measured in four critical propionitrile-hydrocarbon systems covering a wide range of refractive indices as well as the density mismatch between the components. Precritical EKE anomalies are strongly solvent-dependent and they have been observed only in the mixtures with distinctly pronounced critical opalescence and different electric permittivities of the components. The solvent influences the critical amplitude, but not the critical exponent, the latter being close to 0.7 for the examined systems. The possible mechanisms of the field-induced optical anisotropy of the solutions are discussed.

Novel Series of Enaminoketone Liquid Crystals Having Hexatic Smectic B Phase

Abstract Several homologous series of liquid crystals having an aminoketone mesogenic core (Liq. Cryst., 10, 593 (1991)), have been synthesized to derive some new wide-temperature untilted smectics. Compounds belonging to three of six novel series have the hexatic smectic B phase between smectic A and enantiotropic crystal smectic B phases. Eleven of them exhibit first order phase transition between smectic B phases, whereas for other compounds this phase transition is not detectable neither by DSC nor texture studies. Molecular modifications leading to further untitled hexatic compounds are suggested.

Paramagnetic liquid-crystalline complexes based on novel enaminoketone ligands

Abstract Calamitic ligands having aminopropenone-3 ring substituted with alkyl-trans-cyclohexyl-phenyl and alkyl groups are low melting nematogens. Copper(II) complexed to the ligands gives thermally stable rod-like liquid crystals which exhibit an enantiotropic paramagnetic nematic phase. It is shown that modifications of the terminal groups as well as synthesis of asymmetric complexes enables us to extend the nematic range and depress the melting points.

Phenyl-cyclohexyl enaminoketone ligands and their Cu(II) complexes

Abstract The liquid crystalline properties of 1-(alkylamino)-3-[(4″-hexyl-trans-cyclohexyl-4′-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the SA phase in both ligands and complexes, whereas long chains promote SC and crystal H phases for the ligands or SA and SC phases for the complexes. A partly bilayer smectic Ad phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data.

Binuclear liquid crystals incorporating dia- or para-magnetic transition metals

Abstract Discotic binuclear Ni(II) and Cu(II) complexes of 1,2,4,5-tetrakis-(2′-alkyl-2′-homoalkylcarbonylvinylamino)benzene ligands were synthesized. These compounds exhibit columnar liquid crystal phases.

Paramagnetic chiral mesophases of Shiff's base complexes of transition metals

Abstract Copper(II), nickel(II) and oxovanadium(IV) complexes of 4-(4-heptyloxybenzoyloxy)-N-(S)-2-methylbutylsalicylaldimine, as well as the parent ligand, were studied by optical and DSC methods. For the first two complexes, there exist between a tightly twisted chiral nematic phase and the isotropic liquid either some blue phases or novel-type amorphous phases, with their temperature ranges depending significantly on the metal centre. For the third complex, direct isotropization takes place.