摘要:

A polymerizable tunable chiral material (TCM) has been prepared for the fabrication of multicolour reflective cholesteric displays. This photosensitive chiral material, whose chirality is adjustable upon UV irradiation, enables us to adjust the pitch of a cholesteric material and thus to produce the three reflected colours (red, green and blue) for a multicolour reflective cholesteric display. Furthermore, the possibility of linking this compound to a polymer network helped to solve the problem of colour diffusion. Reflection spectra of the corresponding cells show broad reflection peaks, because of scattering from the large amount of polymerizable compound. We also report the difference of response under UV irradiation between this polymerizable tunable chiral material and a non-polymerizable material.

ISSN:0267-8292    

DOI:10.1080/026782998206939

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

New comb-shaped LC copolymers based on phenyl benzoate and menthyl-containing monomers were synthesized. Phase behaviour, optical properties and structure of the synthesized copolymers with different compositions were studied. Specific features of the development of helical nematic and smectic mesophases (N*, NB*, Ncyb*, Nre*, SmA*, SmF*, blue phases) were revealed. Special attention was paid to studying the structure and optical properties of the new chiral NB* mesophase. For this unusual type of mesophase, a model accounting for the arrangement of the mesogenic group is suggested. It is stressed that the subscript B does not mean biaxial (a biaxial N phase is usually denoted Nb) and B refers to the hexagonal ordering of the side groups, similar to that in a SmB phase. An alternative nomenclature would be Nh, where subscript h refers to hexagonal as in Colh0 for a hexagonally ordered columnar phase of a discogen.

ISSN:0267-8292    

DOI:10.1080/026782998206948

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Investigations are reported on the electric field induced orientational transitions in the bend Freedericksz geometry under the action of a stabilizing magnetic field. When the magnetic field is strong enough, the deformation above electric threshold is periodic with the periodicity disappearing at a higher voltage. The alignment does not remain homeotropic below threshold and the sample exhibits pretransitional biaxiality. Every transition is discontinuous and accompanied by hysteresis. The expected form of scaling appears to hold for all the observed thresholds. The thresholds and the direction of the wave vector are frequency dependent, showing that the instability mechanism involves electrical conductivity.

ISSN:0267-8292    

DOI:10.1080/026782998206957

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A phenomenological theory is developed for uniaxial and biaxial nematic phases, based on a two component tensor order parameter. Phase diagrams are plotted and investigated in the plane of two thermodynamic parameters. Anomalies in thermal properties are studied in the vicinity of an isolated four-phase critical point. The temperature dependences of the order parameter and the thermodynamic quantities are also calculated theoretically for the first time.

ISSN:0267-8292    

DOI:10.1080/026782998206966

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

14N nuclear magnetic resonance (NMR) measurements have been carried out for three members of 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxylic acids (ANBC-n, where the number of carbon atoms in the alkoxy group, n, is 14, 16, and 22) in the temperature range 400-500 K. ANBC-16 and-22 show an optically isotropic D phase. The 14N NMR spectrum of the D phase showed a single peak, which may result from isotropically averaged quadrupole interactions around the 14N nucleus. Relaxation time measurements indicate the existence of two relaxational processes, faster anisotropic and slower isotropic motions, and suggest that in both cases ANBC molecules act as a dimer. The present 14N NMR results may be interpreted in the framework of the IPJR model, indicating that the structure of the D phase is a three-dimensional network continuous over the unit lattice.

ISSN:0267-8292    

DOI:10.1080/026782998206975

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

By means of FTIR spectroscopy the quadrupolar order parameter <cos 2 psi> has been determined for the smectic C and C* phases of three mesogenic compounds where the angle psi specifies the rotation around the molecular long axis. The CO vibration and gamma-CH vibration of phenyl groups have been used as spectroscopic probes. The quadrupolar ordering is rather large and different for different parts of the molecules, indicating an internal flexibility. From the spectroscopic data it is deduced that the phenyl rings of the aromatic cores are oriented mainly within the tilt plane. Using the microscopic model of Zeks, the quadrupolar parts of the rotational potential have been found to be in the order of magnitude of the thermal energy, but differ for different parts of the molecules.

ISSN:0267-8292    

DOI:10.1080/026782998206984

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A family of 4-(1,1,7-trihydroperfluoroheptyloxycarbonyl)phenyl 4'-n-alkoxybiphenyl-4-car- boxylates has been synthesized. The compounds show the smectic A phase while the mesogens with intermediate terminal alkyl chain (n 7-12) also exhibit a broad smectic C phase.

ISSN:0267-8292    

DOI:10.1080/026782998206993

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A series of N,N'-(2-chloroterephthalylidene)bis(4-n-alkylaniline)s (CTBAAs) were prepared and their mesomorphic behaviour characterized. None of the homologues showed smectic behaviour, but nematic behaviour with broad mesophases and rather low melting points was seen. The mesomorphic behaviour was compared with that of N,N'-(terephthalylidene) -bis(4-n-alkylaniline)s (TBAAs) and 4,4-bis-(n-alkylbenzal)-2-chloro-1,4-phenylenediamines (BACPDs). An X-ray diffraction analysis of N,N'-(2-chloro-terephthal)bis(4-n-butylaniline) (CTBBA) showed that the molecules were packed in crystals forming a staggered arrangement called an 'imbricated structure'.

ISSN:0267-8292    

DOI:10.1080/026782998207000

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The static critical behaviour of a bulk nematic liquid crystal sample in an oblique magnetic field is analysed. When a magnetic field is applied at a suitable angle alpha with respect to the initially homogeneous nematic director, a spatially inhomogeneous director pattern can be formed. The transition to the deformed state and the formation of walls between the domains resulting from the two equally stable configurations above the transition are studied. The width of the walls is found to diverge at the transition. The critical exponents corresponding to the transition and wall formation are shown to be characteristic of a mean field second order phase transition.

ISSN:0267-8292    

DOI:10.1080/026782998207019

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Polymer dispersed liquid crystal (PDLC) materials were prepared by a polymerization induced phase separation (PIPS) process using UV radiation. The samples were obtained from the liquid crystalline component E7 and a blend of monofunctional (2-ethylhexyl acrylate) and difunctional (1,6-hexane diol diacrylate) monomers as precursors of the matrix. Polymerization energetics and thermodynamic properties of PDLC materials were studied by differential scanning calorimetry. Photopolymerization kinetics and phase behaviour of the PDLC are presented and discussed as a function of UV polymerization conditions (UV light intensity, UV time exposure and isothermal curing temperature).

ISSN:0267-8292    

DOI:10.1080/026782998207028

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor