摘要:

Liquid crystalline 1,1′-disubstituted ferrocene derivatives, 1,1′-bis[ω-[4-(4′-methoxyphenoxycarbonyl)phenoxy]alkoxycarbonyl] ferrocene (abbreviated hereafter to bMAF-n,n= 2∼12, wherenis a carbon number of the methylene chain units), were synthesized, and their phase transition behavior was studied using a differential scanning calorimeter and a polarizing microscope. The liquid crystal structures of the compounds were investigated by the X-ray diffraction method. Nine of eleven compounds of the samples showed liquid crystallinity. The liquid crystalline phases were identified as a nematic (n= 3 and 5∼12), a smectic C (n= 5∼12) and a smectic F or I (n= 11 and 12). As a model structure of the smectic phase, a tilted structure with an expanded substituent is presented.

ISSN:1058-725X    

DOI:10.1080/10587259808042436

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A diepoxy-diamine/liquid crystal mixture (50/50 wt%) is studied in the course of the crosslinking step-polymerization at different isothermal reaction temperatures or with a two temperature cure cycle. Depending on the reaction temperature, the systems undergoe phase separation either isothermally, when the reaction temperature is far below the nematic-isotropic (N-I) temperature of the neat LC, or on cooling partially reacted systems when the reaction temperature is above the N-I temperature of the neat LC.

ISSN:1058-725X    

DOI:10.1080/10587259808042437

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Binary mixtures of HBAB {p-[(p-hexyloxy-benzylidene)-amino] benzonitrile} and CBOOA [N-p-cyanibenzylidene-p-n-octyloxyaniline] exhibit a two phase region where both smectic-A and nematic phase coexists. The reason for this two phase region is discussed by means of Landau formalism. The problem of the first or second order nature of the nematic-smectic-A phase transition is explored. General Landau theory for coupled orientational, translational order parameters and concentration is developed.

ISSN:1058-725X    

DOI:10.1080/10587259808042438

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We derived the expression for the electric field in an isolated spherical droplet of a uniformly oriented uniaxial liquid crystal contained within an isotropic medium, as a function of the dielectric and conductive properties of the materials and of the orientation of the liquid crystal. Results show that the field within the droplet is uniform and that its direction is different from the one of the applied field. Above a certain threshold field intensity the liquid director is reoriented but this simultaneously lowers the field in the droplet. This mechanism contributes to the lack of sharpness in the electrooptic response of PDLC's to an applied field and it must be considered together with the other already known mechanisms. This effect plays a negative role in multiplex addressing applications of PDLC films.

ISSN:1058-725X    

DOI:10.1080/10587259808042439

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A drastic change from a transparent smectic-A (SmA) phase to a light-scattering chiral nematic (N*) one is achieved in [side chain smectic-A liquid crystalline polymer (SCSmALCP)/low molecular weight nematic liquid crystal (LMWNLC/chiral dopant] a ternary composite system with a homeotropic boundary condition. The light-scattering state of the induced N* phase can be resumed into the initially transparent SmA phase on cooling slowly, and be frozen in the SmA phase on cooling rapidly. The effects of the composition of the ternary composite system on such thermo-optical characteristics are investigated.

ISSN:1058-725X    

DOI:10.1080/10587259808042440

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

As one part of the experimental studies on the influence of gas sorption on the surface tension of liquid crystalline substances (LCs), this paper reports on the CO2sorption in low molecular LC MBBA (4-methoxybenzylidene-4′-n-butylaniline) and thus caused the time-dependence of surface tension. The experiments have been performed in the CO2atmosphere over the temperature range which covered the phase transitions of MBBA, and at pressures up to 15 bar.

ISSN:1058-725X    

DOI:10.1080/10587259808042441

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In situobservation of microscopic texture of an unaligned sample of a dimesogenic liquid crystal compound, N-[4-(6-cholesteryloxycarbonyl)pentyloxy-benzylidene]-4-n-butylaniline, called as KI5, was performed under hydrostatic pressures up to 250 MPa by a polarized optical microscope equipped with a high-pressure optical hot-stage. The spherulites of the pressure-induced crystal polymorph(CII) of the KI5 compound, different from those of the normal crystal (CI), were confirmed directly at 100 MPa and higher pressures. The CIIspherulites were grown up from the dark field (homeotropic orientation) of the supercooled smectic phase under high pressures. This observation coincides with the experimental results by high-pressure X-ray diffraction and thermal analysis already reported. The temperature region of homeotropic orientation including partial homeotropic region decreases from ca. 70°C at 0.1 MPa to ca. 47°C at 100 MPa, and then the homeotropic state persists to higher temperatures of about 40 ± 5°C under higher pressures. The homeotropic region shifts to high temperature with the CII-S1transition line by applying pressures above 60 MPa, suggesting that homeotropic orientation of the KI5 compound occurs immediately after the CII-S1transition(melting) at high pressure.

ISSN:1058-725X    

DOI:10.1080/10587259808042442

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Liquid crystalline transition temperatures in 4-(2-and 3-X-benzylideneamino)phenyl 4-alkoxybenzoates, where X = Me or C1, were examined. Although the two substituents are geometrically similar, they affect the nematic-isotropic transition temperature differently. The transition temperature of the 2-Me derivative is higher by 10 to 15°C than that of the 2-C1 derivative, whereas the reverse is true for the 3-X derivatives, the difference being 14 to 21°C. The 3-halogeno derivatives of the higher homologous members exhibit a smectic A phase which is not observed for the parent compounds.

ISSN:1058-725X    

DOI:10.1080/10587259808042443

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Fe-57 Mössbauer Effect was used to study a solution (0.2% by Weight) of 1,1′-diacetylferrocene (DAF) in the liquid crystalline materialp-n-hexyloxy-benzylidene-p-toluidine (HBT). The DAF contained enriched Fe-57. The Mössbauer Effect parameters were determined for the temperature range 100–300K in the crystalline solid phase and 100–200K in the cold smectic ß phase of HBT. Here “cold” means the smectic glass and the supercoded smectic phase. The Ln recoil-free intensity (f)vsTdata exhibited linear Debye behavior for the solid phase over the entire temperature range. The low temperature (T< 190) portion of the cold smectic InfvsTdata also exhibited Debye behavior, and the smectic glass gave a Mössbauer-Debye temperature (θlc) about 30 K. lower than the crystalline phase. The smectic glass-super cooled smectic transition was determined to beTg= 190 K from the deviation of the InfvsTdata from linear behavior. AboveTg, the deviation from linear Debye behavior followed a (T-Tg)2dependence. The smecticBglass yielded an order parameter ofS= 0.06 for DAF molecules at 100 K. Rotational and transitional diffusion were not observed for the cold smecticBphase.

ISSN:1058-725X    

DOI:10.1080/10587259808042444

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The structure of a mono-substituted ferrocene derivative of which the flexible spacer is located between the ferrocenyl and mesogenic groups, ω-[4-(4-methoxyphenoxycarbonyl)phenoxycarbonyl]propyl 4-ferrocenylbenzoate was determined by the X-ray diffraction method. It was found that the two cyclopentadienyl rings in the ferrocene and the—C3H6—chain introduced as a flexible spacer exhibited a very interesting conformation. The two cyclopentadienyl rings are a staggered conformation rather than an eclipsed one. This staggered conformation is an unusual structure in mono-substituted ferrocene derivatives, in general. Also, the—C3H6—chain includes twogaucheconformations and makes a bent molecular feature rather than a rod-like one. As a result, the title compound does not exhibit liquid crystallinity.

ISSN:1058-725X    

DOI:10.1080/10587259808042445

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor