摘要:

Ion bearing liquid crystalline compounds based on trans-1,2-bis (4-pyridinium) ethylene were synthesized and studied. These compounds included low molecular mass analogues, twin model compounds and main chain ionomers. Most of these exhibited liquid crystallinity of the smectic type. As a general rule the introduction of charges into the mesogenic moiety increased the stability (transition temperature) of the mesophase. Large supercooling effects, broad mesophase intervals and tendency to polymorphism are common features of these ionic mesogenic compounds.

ISSN:1058-725X    

DOI:10.1080/10587259508037319

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

As starting materials for liquid crystalline polyesters, a number of bis [4-(ω-alkenyloxybenzoyl)oxy arenes (arising from the diols hydroquinone, 4,4′-biphenyldiol, 1,6-di(4-hydroxyphenyl)hexane, 2,7-fluorenediol and 2,7-fluorenonediol) have been synthesized and characterized by their elemental analyses, IR,1H NMR and MS. These esters exhibit liquid crystalline phases. The mainly nematic and in two cases also smectic phases have been studied by DSC and polarizing microscopy.

ISSN:1058-725X    

DOI:10.1080/10587259508037320

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The solid phases which appear when heating crystalline bisn-decyl andn-dodecyl ammonium tetra-chlorozincates (C10Zn and C12Zn for short) were studied using differential scanning calorimetry, X-ray diffraction and infrared and Raman spectroscopies. The unit-cell parameters of the different phases were determined. For C10Zn as well as for C12Zn, the room temperature stable phase is a well-ordered interdigitated layer structure with chains in all-trans conformation. A great mobility of the chains is observed when raising temperature within the phase, but the formation of specific sequences of bonds, mainly kinksgt2n-1g′ and end gauche forms, abruptly occurs at the first transition temperature at the same time as the cell parameters change. The consecutive increase in the chain diameter induces a partial disinterdigitation. A second phase change at higher temperature leads to a highly disordered form in which only the inorganic matrix keeps a bidimensional crystallographic organization, before reaching the isotropic phase.

ISSN:1058-725X    

DOI:10.1080/10587259508037321

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Varied blend systems containing Imine-based side chain liquid crystalline polysiloxanes or ladderlike polysilsesquioxanes and corresponding low mass liquid crystal (LC) analogues were prepared by blending or crude solution mixing. In later case, in situ crosslinking took place by hydrolysis and further condensation of remained Si-H groups in the macromolecules. Electro-optic measurement results indicate rise time and optical contrast of the blend system are related to the polarity and applied voltage: the blend system containing a weak polar component exhibits lower optical contrast and “recovery” effect, meanwhile, strong polar blend system exhibits “memory” effect; short rise time and lower driving voltage for the PNLC (Polymer Network Liquid Crystal) system containing low content of polymer are similar to that of ordinary low mass LC system. Some peculiar behaviour may be caused by the “anchoring” effect and elastic deformation of the cavity. The blend system containing ladderlike polysilsesquioxane exhibits sharp electro-optic behaviour and distinct thresold voltage.

ISSN:1058-725X    

DOI:10.1080/10587259508037322

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Molecular dynamics (MD) simulations were carried out to investigate the effect of the quadrupole moment on the orientational order in polar liquids. A simple model of soft sphere with a point dipole and a linear quadrupole was employed in the current study. It is found that the quadrupole moment shifts the isotropic to ferroelectric nematic and the ferroelectric nematic to solid phase transitions to higher density. The columnar order appears at much lower temperature as compared with the pure dipole liquid.

ISSN:1058-725X    

DOI:10.1080/10587259508037323

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Seven alkylene aromatic polyimides have been synthesised. FT-IR spectra for the polyimides show small regular changes. This shows that the bulk structure of these polyimides changes in a regular fashion, while SEM pictures do not reveal any difference in the surface topology.

ISSN:1058-725X    

DOI:10.1080/10587259508037324

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Infrared reflection absorption spectroscopy (IR-RAS) was applied to analyze the spontaneous orientation behavior of alkyl and alkoxy cyanobiphenyl liquid crystals on the metallic substrate. The long axis of the liquid crystal molecules was shown to orient perpendicular to the substrate plane. The orientation function was evaluated from the relative intensity of the CN stretching vibration and the out-of-plane deformation of the biphenyl ring. The temperature dependence of orientation functions was studied using a heating and cooling apparatus. The orientation functions gradually decreased with the rise in temperature in the liquid crystal phase and fell off to the range of 0.1-0.2 above liquid crystal - isotropic transition. The orientation function of the terminal methyl group was evaluated from the relative intensity of the symmetric and asymmetric stretching vibrations of the methyl group. The orientation of the methyl group was discussed in relation to the conformation of the methylene sequence.

ISSN:1058-725X    

DOI:10.1080/10587259508037325

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Brillouin scattering as a function of scattering angles from 180° to ∼10° has been measured in the nematic phases of two liquid crystal mixtures, E. Merck ZLI-2861 and E7, without any preferred orientation. Such measurements at room temperature cover the frequency range from ∼10 to ∼1 GHz. The behavior of both the frequency shifts and linewidths is explained by a single time internal relaxation process with the characteristic frequencies 3.2 (ZLI-2861) and 1.2 (E7) GHz respectively. The behavior of the hypersonic attenuation shows no correlation with the static bulk viscosity in the nematic phase.

ISSN:1058-725X    

DOI:10.1080/10587259508037326

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Four new CT salts with Cu-containing binuclear polyhalide complex anions ET3Cu2Brx(x∼ 5) (A), ET3Cu2CI4(B), (TTM-TTF) Cu2Br4.72(C), and (TTM-TTF), Cu2Cl6(D) [ET = BEDT-TTF = bisethylenedithio-tetrathiafulvalene, TTM-TTF = tetrathiomethyl-tetrathiafulvalene are prepared and the degree of charge transfer as well as the valence states of the Cu atom in the four CT salts are discussed based on the analysis of X-ray photoelectron spectroscopy. The conductivity of the four charge-transfer salts A, B, C, and D at room temperature and their temperature dependence from room temperature down to 77 K along the crystal growth direction are reported. A behaves metallic down to about 250 K, then turns to a semi-conductor; B is an organic metal down to liquid nitrogen temperature; C shows a semi-conducting behavior down to about 230 K, then turns to an insulator and D is an insulator. The crystal structures of C and D are determined. In crystal C, both donors and acceptors occupy symmetry centers in the cell and are stacked in segregated columns. We have observed short intracolumnar and intercolumnar S…S contacts of 3.214(10), 3.417(12)Å, respectively in the donor columns; the binuclear poly bromide metal complex acceptor anions are planar and stacked forming complicated polymeric columns along the b axis, the Cu atom of each of the polymeric columns is five-coordinate. In crystal D, the donor molecules TTM-TTF form dimers and the plane is almost perpendicular to that of the metal complex anion (Cu2Cl6)2-.

ISSN:1058-725X    

DOI:10.1080/10587259508037327

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Pople and Karasz theory of melting of molecular crystals, which is based on the theory of melting of inert gas crystals by Lennard-Jones and Devonshire, is extended using a third energy parameter,W″. The extension is done as follows: the previous repulsive energy parameterWis divided into two parts. The first part is the interaction between molecules which are on different sites with the same orientations, called againW. The second is the interaction between molecules on different sites and also different orientations, namelyW″.W″ is combined with the previousW′ and the newWenergy parameters by the arithmetic mean including an adjustable parameter. The thermodynamic properties are evaluated by the Bragg-Williams approximation. The theory is applied to plastic crystals and compared with the Pople and Karasz theory. By introducing a physical realistic coupling between orientational and positional order, ν, the theory gives a solid state rotational transition and melting transition. For values of ν ≤ 0.331 the two transitions are separate, while for values of ν ≤ 0.331 they coalesce. The quantitative predictions of the theory is compared with experimental results for plastic crystals by plotting entropy and volume changes versus melting/boiling temperature ratios. The agreement between our theory and the experimental data is better than the calculations of the Pople and Karasz theory, as result of the introduction of the parameterW″ in the present theory.

ISSN:1058-725X    

DOI:10.1080/10587259508037328

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor