摘要:

The molecular ordering of the liquid crystal 8CB near a surfactant-coated glass surface has been studied using evanescent-wave ellipsometry. Surface molecular ordering was measured in the isotropic phase, and both bulk and surface ordering were measured simultaneously in the nematic phase in the vicinity of the nematic-isotropic transition temperatureTNI.Two kinds of behavior were observed, depending on the strength of the surface-liquid crystal interaction in a given sample. (1) For samples with a strong surface-liquid crystal interaction, at temperatures aboveTNIthe interface is wet by a homeotropically oriented, ordered layer whose thickness diverges as the temperatureTapproachesTNI. ForT < TNI, the interface is wet by an surface region of enhanced nematic order whose thickness increases asT → TNIbut remains finite atTNI. (2) For samples with a weak surface-liquid crystal interaction, at temperatures aboveTNIthe interface is wet by an ordered layer whose thickness increases but remains finite asT → Tni. ForT < TNI, the interface is wet by a disordered surface region whose thickness increases but remains finite asT → TNI. The results are analyzed in terms of the Landau-de Gennes theory and found to be in qualitative agreement with theoretical predictions.

ISSN:1058-725X    

DOI:10.1080/10587259808045653

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

I. 3,5-diphenyl triazole, C14H11N3, Mr = 221.26, monoclinic,Cc, a= 26.982(6) Å,b= 5.6806(14) Å, c = 7.439(2) Å, β = 105.54(2)°,V= 1098.6(5) Å3,Z= 4,Dm= 1.312gm·cm−3,Dc= 1.338gm·cm−3, μ = 0.083cm−1,F000= 464, (MoKα) = 0.71069 Å, finalR1 andwR2 are 0.0335 and 0.0985 respectively. Hydrogen bonds of the type CH···N are observed in the crystal structure of the compound. The molecules are packed in layers when viewed alongbandc, whereas downait shows a herringbone type of arrangement.

ISSN:1058-725X    

DOI:10.1080/10587259808045654

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Raman spectra of Terepthalylidene-bis-p-n-declyaniline (TBDA), have been recorded as a function of temperature in the temperature range from 55.0°C (solid) to 199.0°C (isotropic liquid) in the 1100–1200cm−1and 1520–1650cm−1regions. The precise values of peak positions, integrated intensities and linewidths of some selected Raman bands have been obtained by deconvoluting the bands. The changes in the molecular alignment and its effect on inter/intra molecular interactions at two particular phase transitionsviz., solid-smecticG (K-SG) and smecticI-SmecticC (SI-Sc) have been discussed on the basis of variation in the Raman spectral parameters with temperature. From detailed considerations, it is inferred that the increased orientational/vibrational freedom of long alkyl chain on the core is responsible for major spectral changes at theK-SGtransition while the changes in the intramolecular interactions of the core part with increased fluidity, is responsible for spectral anomalies at theSI-Sctransition.

ISSN:1058-725X    

DOI:10.1080/10587259808045655

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

To explore the effect of orientation of monomers and polymerization procedure on polymerization behavior, thermal polymerization and photopolymerization of vinyl monomers having a biphenyl structure were conducted at various temperatures. It was found that the initial rate of polymerization and conversion increased with temperature despite phases of the monomer. It was also observed that Arrhenius plots for the initial rates of photopolymerization fell on a straight line, while those of thermal polymerization changed the slope at the smecticisotropic or nematic-isotropic phase transition temperature. The number-average molecular weight of the polymer produced in the thermal polymerization in the smectic phase was higher than that in the isotropic phase, whereas that of the polymer obtained by photopolymerization in the smectic phase was lower than that in the isotropic phase. These results suggest that polymerization behavior is affected by the initiation method in the polymerization of liquid-crystalline monomers.

ISSN:1058-725X    

DOI:10.1080/10587259808045656

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The structure of a monosubstituted ferrocene derivative of which the flexible spacer is located between the ferrocenyl and mesogenic groups, ω-[4-(4-methoxyphenoxycarbonyl)phenoxycarbonyl]butyl 4-ferrocenylbenzoate was determined by the X-ray diffraction method. The -C4H8- chain introduced as a flexible spacer is an all-transconformation. The molecule is slightly bent around the ester group to the phenyl ferrocenyl group in order to form a rod-like structure. The molecular geometry is a rod-like feature, and two cyclopentadienyl rings exhibit an eclipsed conformation rather than a staggered one. As a result, this bent structure can lead to efficient packing because it is suitable to make up a bulk of unsubstituted cyclopentadienyl ring, and may play an important role in the appearance of the liquid crystal phase. The molecules are arranged in layers just like the smectic phase of the liquid crystals.

ISSN:1058-725X    

DOI:10.1080/10587259808045657

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Electrochemically polymerized polypyrrole (PPy) films with different dopants showed different surface energies. The films were used as alignment layers of liquid crystal displays (LCDs). The PPy films doped with ClO4−(PPy/ClO4) and PF6−(PPy/PF6) showed surface energies of 43.2 and 32.3 mJ/m2, respectively, while the pretilt angles of 4-cyano-4′-pentylbiphenyl on the films were 5.6 ± 0.3 and 14.0 ± 2.2 degrees, respectively. The electro-optic response time measured by light transmittance through the twisted nematic(TN) LCDs on switch-on was shorter for the display with PPy/PF6than for that with PPy/ClO4. However, the turn-off response time was shorter for the display with PPy/ClO4than for that with PPy/PF6. The total response time, which is the sum of the turn-on and turn-off response times, was 75 and 120 msec at 3.0Vppfor the displays with PPy/ClO4and PPy/PF6, respectively.

ISSN:1058-725X    

DOI:10.1080/10587259808045658

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

High pressure investigations have been carried out on four successive homologues of the hexa-n-alkoxy triphenylene series exhibiting the hexagonally ordered columnar mesophase. The most remarkable feature is that the slope of the mesophase to isotropic phase boundary (dT/dP)1 barshows a strong decrease with increasing chain length becoming zero for the 8th homologue. To explain this feature we propose an argument based on the ratio of the volume of the triphenylene core to the total volume.

ISSN:1058-725X    

DOI:10.1080/10587259808045659

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Diphenyl perdeuterated adipate and tetradecanedioate, and three different, selectively deuterium labeled 2-[6-[4-[(4-cyanophenyl)azo]phenoxy]hexyl]-1,3-propanediols have been prepared by exchange and reduction techniques.1H and2H NMR spectroscopic investigations have revealed the deuterium exchange in the esters to be higher than 93% and evenly distributed. Similarly, a varying but high deuterium exchange was detected in the selectively labeled diols. All deuterated samples were additionally characterized in detail by13C NMR spectroscopy; the deuterium isotope effect conclusively assisted some of the shift assignments. No isotope effect could be detected by visible spectroscopy in any of the deuterated diols. On the other hand, FTIR in all deuterated compounds reveals a substantial frequency shift of all carbon-deuteron vibrations as compared to the corresponding carbon-hydrogen vibrations. Polarizing optical microscopic and differential scanning calorimetric investigations have identified all the deuterium labeled diols as monotropic liquid crystals with both nematic and smectic A phases.

ISSN:1058-725X    

DOI:10.1080/10587259808045660

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two sets of specifically deuterated cyanoazobenzene side-chain polyadipates and polytetrade-canedioates have been prepared by transesterification in the melt. Combinations of three different, selectively deuterium labeled 2-[6-[4-[(4-cyanophenyl)azo]phenoxy]hexyl]-1,3-propanediols or the non-deuterated analog and diphenyl adipate or tetradecanedioate in perdeuterated or non-deuterated versions were employed. The polyesters have weight average molecular masses in the range 21 000–183 000 as determined by SEC. The phase behaviour of the polyesters have been investigated in detail by differential scanning calorimetry. Whereas the polytetradecanedioates show a complex thermal behaviour with a number of different phases, the polyadipates are less complex and both nematic and smectic A phases have been identified by polarizing optical microscopy. Solution1H,13C and2H NMR spectroscopy have been utilized for both polyester structural assessment and determination of deuterium distribution and content. FTIR spectroscopy has revealed suitable and characteristic vibrations which unequivocally represents the absorption behaviour of individual polyester segments or molecular structures in the different selectively deuterated polyesters.

ISSN:1058-725X    

DOI:10.1080/10587259808045661

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The structure, resistivity and ESR of a new molecular charge transfer salt β-(salt (BEDT-TTF)4• H2O • Fe(C2O4)3• C6H5NO2(BEDT-TTF = bis (ethylenedithio)tetrathiofulvalene) are studied. The structure of the salt consists of successive layers of BEDT-TTF which are packed according to β-type and layers of approximately hexagonal geometry containing alternating H2O and Fe(C2O4)33−, with C6H5NO2lying within the hexagonal cavity. Its main crystallographic parameters are found to be:M= 1999.6(1),a= 10.31(8),b= 20.14(8),c= 35.34(4) Å,β= 92.21(9)°V= 7342.0(5) Å3, space group C2/c; Z = 4. The conductivity of this salt at room temperature is l0 Scm−1and shows semiconducting behaviour from 20 to 300K. The ESR line width is found to be 38.1 (300 K), which is substantially wider than a typical line width for BEDT-TTF based radical cation salts of theβ-type, indicating a two-dimensional character. The comparison of crystal structure and properties of the title compound with other salts of this family (BEDT-TTF)4• A • Fe(C2O4)3• C6H5NO2, whereA= H2O, K+or NH4+, is also carried out.

ISSN:1058-725X    

DOI:10.1080/10587259808045662

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor