摘要:

For some problems in liquid crystal physics we need to use the Euler equation and the corresponding boundary equation in the three-dimensional case with soft boundaries. As a further complication the free energy expression, which should be minimized, might contain some second-order and third-order derivatives. These higher-order derivatives will cause the spatial derivatives of the boundary normal to appear in the boundary equation. Explicit formulae are given for the Euler equation and the corresponding surface equations for a general case. As an example, the theory is applied to nematic liquid crystals, where the general Euler equations and surface molecular fields are derived, including the effects of an imposed electric field.

ISSN:0267-8292    

DOI:10.1080/02678299508036677

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

New thermotropic ionic liquid crystals were prepared fromtrans-4-nitro-4′-stilbazole and alkyl halides.trans-N-Alkyl-4-nitro-4′-stilbazolium bromides containing alkyl chains with 7 to 10 carbons and the chloride homologues containing alkyl chains with 5 to 10 carbons exhibited smectic phases. For example,trans-N-decyl-4-nitro-4′-stilbazolium bromide andtrans-N-hexyl-4-nitro-4′-stilbazolium chloride showed smectic phases from 175 to 186°C and from 129 to 190°C, respectively. The temperature range of mesophases increased with decreasing size of the counteranions. The miscibility oftrans-N-alkyl-4-nitro-4′-stilbazolium bromide in Schiff's base compounds having various electronegative groups was examined by differential scanning calorimetry and polarizing microscopy. Miscible binary mixtures were prepared fromtrans-N-alkyl-4-nitro-4′-stilbazolium bromides and 4-alkoxy-N-(9-methyl-2-carbozolyl-methylene)anilines. The 1:1 (mole ratio) binary mixture oftrans-N-hexyl-4-nitro-4′-stilbazolium bromide with 4-hexyloxy-N-(9-methyl-2-carbazolylmethylene)aniline exhibited a stable smectic phase between 83 and 149°C, though a smectic phase is not exhibited by both individual components. The miscibility in the binary mixtures might be caused by a combination of ionic and electron donor-acceptor interactions.

ISSN:0267-8292    

DOI:10.1080/02678299508036678

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The tetrones represent an interesting new mesogenic building block. The results of this study show that they can be incorporated into a variety of mesophases. A smectic phase was observed in the polycatenar compound with four terminal chains as expected. The phase exhibits a tilted structure (Scphase) to prevent void formation. The compound with six pendant chains forms a columnar phase. In spite of their structural similarity, the tetrones studied tended not to be completely miscible. However, complete miscibility with a semi-discoid phenylhydrazone was observed. When this hydrazone, which forms a columnar ‘Dhophase’, was mixed with tetrone which forms a columnar ‘Dhdphase’ a columnar hexagonal phase was produced with enhanced stability. We believe that the stability enhancement derives from a charge transfer interaction between the tetrone and the phenylhydrazone.

ISSN:0267-8292    

DOI:10.1080/02678299508036679

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The switching behaviour of 1,3,6,8-tetrakis-((S)-2-(heptyloxy)propanoyloxy)pyrene was studied near room temperature in a monotropic columnar phase. The switching angle (optical tilt angle) increases linearly with the applied electric field from 0° toc. ± 10° at ± 0.35°/(V μm−1), then rapidly increases to its upper limit of 22°. The electric polarization is roughly proportional to the switching angle with a maximum value of 110nC cm−2at high field strengths. At field strengths up to 10 V μm−1, a voltage and temperature independent 0 to 90 per cent switching time ofc. 650 μs was measured. The observations are explained in terms of deformation and unwinding of an intracolumnar helix.

ISSN:0267-8292    

DOI:10.1080/02678299508036680

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new optically active (R)-3-ethylmercapto-2-methylpropionic acid has been synthesized usingD(-)—2,10-camphorsultam as a chiral auxiliary. The optical purity of the acid obtained was greater than 98 per cent. Its derivatives, (R)-4-(3-ethylmercapto-2-methylpropionyl)phenyl 4′-alkoxybiphenyl-4-carboxylates (EMMPPmBC;m= 7–16), have been prepared for the investigation of liquid crystalline properties as a function of peripheral alkyl chain length. Optical studies showed that all members exhibited an antiferroelectric S*cAphase. The results also indicate that a lengthened alkyl chain length is favoured for ScA* phase formation.

ISSN:0267-8292    

DOI:10.1080/02678299508036681

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have measured the pretilt angle induced by rubbed polymer films in a smectic A and in a nematic liquid crystalline medium using an optical phase retardation method. The pretilt angle was found to depend on the liquid crystalline phase (smectic A versus nematic) and on the smectic layer structure (chevron versus tilted-bookshelf). The occurrence of the different smectic layer structures was verified by X-ray diffraction measurements. The effect of the applied rubbing energy on the pretilt angle obtained is measured.

ISSN:0267-8292    

DOI:10.1080/02678299508036682

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new series of glass-forming molecular materials have been synthesized that incorporate 1-phenyl-2-(6-cyanonaphth-2-yl)ethyne as the high optical birefringence nematogenic moiety and a diphenylacetylenic group as part of the chiral moiety containing (S)-(−)-1-phenylethanol. To facilitate the preparation of chiral nematic systems, the key intermediate, i.e. 1,3,5-cyclohex-anetricarboxylic anhydride chloride, was synthesized and characterized. The thermotropic and optical properties of all products and the blends prepared therefrom were characterized by polarizing optical microscopy, differential scanning calorimetry, and UV-VIS-NIR spectrophotometry. It was found that all the resultant molecular materials readily form glasses with aTgof around 60°C while showing no residual crystallinity belowTgor tendency toward crystallization by heating aboveTg. Furthermore, binary blends showed a decreasing degree of miscibility at an increasing extent of structural dissimilarity with the all-chiral/all-nematic systems exhibiting significant phase separation at a chiral mole fraction of 0.16.

ISSN:0267-8292    

DOI:10.1080/02678299508036683

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The nematic phase and the viscous isotropic (VI) phase formed by solutions of CTAB and SHNC are investigated using light scattering and viscosity techniques. It is argued that the turbidity in the nematic phase is due to orientational fluctuations in the director and therefore the intensity scales asQ−2. It is shown that with dilution of the nematic phase with water the turbidity disappears with a simultaneous increase of viscosity.

ISSN:0267-8292    

DOI:10.1080/02678299508036684

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this paper, the syntheses, phase properties and ferroelectric properties of new liquid crystalline oligosiloxane dimesogens are described. Smectic phases are dominant in this class of materials. Spontaneous polarizations are in the range of 10 to approximately 100 nCcm−2. The materials show interesting properties for display applications. Although offering higher mechanical stability than low molar mass materials, their switching is significantly faster (switching times in the range of some 10−5s) than is the case for similar side group polymers (typically some 10−3s). Therefore these new oligosiloxane derivatives may be ideal for building flexible displays. In addition, mixtures of oligosiloxane dimesogens were compared with copolymers and with siloxane-free low molar mass materials bearing the same mesogenic groups. The results support the idea of a ‘virtual polymer backbone’, which is formed by a microphase separation phenomenon. Dimesogenic siloxane mixtures and copolymers behave quite similarly, while the siloxane-free mixtures show a different phase behaviour.

ISSN:0267-8292    

DOI:10.1080/02678299508036685

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A comparative study of the liquid crystal and ferroelectric properties of several achiral, racemic and non-racemic 2,6-naphthyl benzoates and their 1,4-phenyl benzoate analogues is reported. In terms of pure compounds, both central core structures give rise to similar mesophase sequences; however, the naphthalene derivatives exhibit broader and more thermally stable liquid crystalline states. On the other hand, both central core units give rise to equivalent electric and optoelectronic properties when the compounds are used as chiral dopants in ferroelectric liquid crystal mixtures.

ISSN:0267-8292    

DOI:10.1080/02678299508036686

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor