摘要:

We develop an analytical approach to study the propagation of optical fields through a nematic slab model with hybrid boundary conditions studied numerically by Linet al.[I]. For a low intensity beam we first derive the eikonal equation and from it we then calculate the ray trajectories in the limit of geometrical optics. We show that there may exist caustics within the slab. Then we consider the WKB limit and calculate the field transverse magnetic modes, their number and their cutoff frequencies. We show that for both limits the agreement between the analytical and numerical results for the propagation constants is excellent, when caustics are not present; however, their presence introduces larger differences in the values of the calculated field amplitudes but the comparison is still quite good. We show that these discrepancies have their origin in the fact that the chosen parameter values in the exact numerical calculations, do not lie within the limits of validity of our WKB approximation. Thus, a more precise comparison between these approaches requires different sets of values of the relevant parameters. Finally, we discuss the scope and limitations of our method.

ISSN:1058-725X    

DOI:10.1080/10587259808047112

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Octyl benzoic acid, CH3(CH2)7C6H4COOH(OBA), Mr = 234.34, triclinic,Pl,a= 13.6372 Åb= 22.0910Å,c= 7.6816 ÅV= 2156.69 Å3,Z= 1,Dm= 1.079 gm cm−3,Dc= 1.083 gm cm−3, μ = 0.07 cm−1, F000= 768, (MoKα) = 0.71069A, finalR1 andwR2 are 0.0456 and 0.1265 respectively.

ISSN:1058-725X    

DOI:10.1080/10587259808047113

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper relates a comparative study of crystal structures of two isomeric compounds. They differ only through their polyaromatic group sequence: O—ø—CO2—ø—C ≡ C—ø—CO2on the one hand and O—ø—C ≡ C—ø—CO2—ø—CO2on the other, and give rise to very different polymorphisms. The chiral mesogenic (S) 1-methylheptyl 4-[(4-octyloxy-3-fluoro) benzoyloxy]tolan-4′ carboxylate (8FBTOlM7) crystallizes in the P212121space group, with two different molecules A and B per asymmetric unit (Z= 8) witha= 7.903(2),b= 11.324(1) andc= 80.576(6)Å. The polyaromatic central cores of both molecules are parallel and aligned in the same direction, giving dimers with a tilt angle close to 11°. The molecules give rise to sheets, of which the arrangement is smectic C and is antiferroelectric-like. The repetitive unit in the crystal phase is a bilayer one, where molecules are alternatively tilted from one layer to the other. The molecular arrangement is compared with that of the (S) 4-[l-methylheptyloxy-carbonyl] phenyl 4-heptyloxytolan-4′ carboxylate (7TBOlM7) which gives rise to a very rich polymorphism, including ferro-, antiferro- and ferri-electric phases. The binding energy within a sheet and between neighbouring sheets was evaluated by using molecular mechanics for both compounds. It seems that the relative positions of the benzyl and tolan groups inserted between the polar ester and ether groups in the polyaromatic central core, is of a prime importance in the molecular arrangement and consequently in the mesomorphic sequence.

ISSN:1058-725X    

DOI:10.1080/10587259808047114

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Laterally 4-nitrobenzyloxycarbonyl substituted three-ring compounds preferably exhibit smectic A phases. However, induction of smectic C phases can be observed in binary mixtures with mesogens having a similar molecular shape but not a strongly polar group at the laterally positioned phenyl ring. The scale of phase induction depends on the length of terminal alkyl chains, type and position of substituents as well as the length of the flexible spacer linking the lateral aryl group to the basic mesogen. X-ray investigations of selected mixtures verify that the structure of induced smectic C phases is intercalated comparable to orthogonal phases of lateral aryl substituted mesogens.

ISSN:1058-725X    

DOI:10.1080/10587259808047115

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Cholesteric liquid crystal polysiloxane oligomers can be prepared in the Grandjean texture and fractured into smaller pieces called flakes. These flakes function as discrete domains whose degree of orientation can be evaluated by means of Fergason's Equation and turbidity. Further, these flakes can be embedded in a carrier providing a mixed system analogous to polymer-dispersed or gel systems. These embedded flakes have applications as color coatings and polarizing paints and inks without the limitations of elevated temperature or applied voltage.

ISSN:1058-725X    

DOI:10.1080/10587259808047116

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The selective reflection profile of a cholesteric liquid crystal is asymmetric when (a) for light incident parallel to the cholesteric helix axis, the incident polarization vector,E, is at an angle other than 45° to the molecular director at the first surface or (b) for light incident oblique to the cholesteric helix axis, the incident polarization is S- or P-polarized. We confirm these effects using cyclic polysiloxanes. Further, we show that the use of a new form of cholesteric liquid crystal called flakes allows the first experimental separation of the asymmetry due to the surface and that due to the bulk.

ISSN:1058-725X    

DOI:10.1080/10587259808047117

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The mesomorphic properties of 4-(4 alkoxybenzylideneamino)phenyl 2- and 3-X-benzoates, whereX= Me or Cl, were examined. While the nematic-isotropic transition temperatures of the 2-Me and 2-Cl derivatives are nearly identical, the 3-Cl derivatives give higher transition temperatures than the 3-Me derivatives, the difference being 20°C or more. The nematic phase given by the lower homologous members of the 2-Me derivative is thermally more stable than that of the 3-Me derivative but this relation is reversed for the higher members. In contrast to the purely nematogenic parent compounds, the 3-halogeno derivatives of the higher homologous members exhibit a smectic A phase.

ISSN:1058-725X    

DOI:10.1080/10587259808047118

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Surface hydrogenation reaction was performed in order to clarify the mechanism of photoalignment using poly(vinyl cinnamate) (PVCi). The reaction makes it possible to remove any surface ordering of the cinnamate side groups, which may happen during the photoalignment process while the generated photoproducts are still intact. After considering LC alignment and the azimuthal anchoring energy of the hydrogenated PVCi/E7 cells, it was confirmed that the alignment of liquid crystal molecules is mainly induced by the photoproducts.

ISSN:1058-725X    

DOI:10.1080/10587259808047119

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

It has been shown that a polymer network, formed in the SmA phase by UV photocure of photocurable liquid crystalline monoacrylates that are doped in a surface-stabilized ferroelectric liquid crystal (SSFLC), eliminates zig-zag defects in the SmC* phase, Since a chevron layer structure is transformed into a quasi-bookshelf layer structure by the polymer main chain. In this study, we have observed the electrooptical (EO) effect of this polymer-stabilized SSFLC (PS-SSFLC) with the aim of exploring the effect of the liquid crystalline polymer network on the alignment structure of FLC molecules. As experimental results, it was found that liquid crystalline side chains bond strongly with a main chain and attract FLC molecules in the rubbing direction. Furthermore, we propose and demonstrate a new PS-SSFLC fabricated also by UV photocure of doped monoacrylates particularly at a temperature where the LC medium is in the SmC* phase under the simultaneous application of a monopolar electric field. This device exhibits monostable EO characteristics with a high contrast ratio owing to being defect free, having grayscale capability without threshold, and a fast response speed.

ISSN:1058-725X    

DOI:10.1080/10587259808047120

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Mesogenic monomers of 4-[6-(acryloyloxy) hexoxy] benzoic acid (AHB) and 4-[[6-[(2-methyl-l-oxo-2-propenyl)oxy]hexyl]oxy]-benzoic acid 4′-[(1-oxo-10,12-nonadecadiynyl)-oxy]-[1,1′-bi-phenyl]-4-yl] ester (MHNB) are prepared for polymerization in highly ordered smectic and nematic mesophases and liquid crystal solvents. AHB exhibits smectic C and nematic mesophases, whereas MHNB displays the phase sequence of smectic X, C, A and nematic phases. The highest molecular-weight polymers with the widest molecular-weight distribution were found in polymerization of the highly ordered smectic phase and using smectic solvents. Photopolymerization in nematic systems gave the narrowest molecular weight distribution polymers when compared with those in other systems.

ISSN:1058-725X    

DOI:10.1080/10587259808047121

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor