摘要:

We present a new model to study in-plane liquid properties of lipid membranes. The different conformations of lipids are represented by a seven-state system of hard triatomic particles, or triples, of varying lengths which correspond to the different cross-sectional areas of the lipids in the plane of the membrane. Two-dimensional Monte Carlo simulations are performed in both the constant NVT and NPT ensembles. The distribution of states has a strong density dependence and a small temperature dependence over the biologically relevant range. There is no long range orientational order in the systems before freezing. The short range orientational order increases with density. Widom's particle insertion method is used to obtain the excess chemical potential of the system for the seven states. These values, along with the pressure, are in excellent agreement with estimates from scaled particle theory.

ISSN:0267-8292    

DOI:10.1080/02678298808086392

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Neutron quasielastic scattering has been used to study molecular reorientation in pure 4-ethyl-4'-n-pentylazoxybenzene (EPAB), 4'-n-pentyl-4-cyanobiphenyl (5CB), 4-(trans-4'-n-hexylcyclohexyl)isothiocyanatobenzene (6CHBT) and in EPAB-5CB and EPAB-6CHBT mixtures. 5CB exhibits a much narrower quasi-elastic component than EPAB. We interpret this as an indication of 5CB dimerization, which causes steric hindrance to reorientation. The equimolar mixture of EPAB-5CB exhibits a significantly broader quasielastic component than that evaluated from additive contributions of the pure constituents. We interpret this as a result of complexing of 5CB and EPAB molecules, after destruction of 5CB dimers. The complex pairs DM DM DM … probably form immediately a DMDMDM … smectic layer in which individual pairs cannot be distinguished, and in which the steric hindrance to reorientation is no longer present. This picture is supported by measurements at other concentrations of EPAB and 5CB. The EPAB-6CHBT mixtures, on the other hand, show a much more additive behaviour of the constituents.

ISSN:0267-8292    

DOI:10.1080/02678298808086393

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The optical microscopic mass transport technique has been used to study diffusion phenomenon in a chiral nematic/nematic solute/solvent mixture. Analysis of the concentration-distance, concentration-time and distance-time of the diffusion profile gave the diffusion coefficient of the system as a function of time, distance and concentration, respectively. The mutual diffusion coefficient of the system was independent of the distance and time, showing an average value of 2.65 × 10−7cm2s−1. In non-steady state diffusion, the diffusion coefficient was dependent on both distance and time. The diffusion coefficient exhibited an inverse relation with the local concentration of the chiral solute. The self-diffusion coefficient of the nematic solvent gave a value of 3.4 × 10−7cm2s−1via extrapolation to zero concentration of the solute.

ISSN:0267-8292    

DOI:10.1080/02678298808086394

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Rotational viscosity and spontaneous polarization are the most important properties of a ferroelectric liquid crystal with regard to its switching time in surface stabilized or a.c. field stabilized displays. Whereas there is an abundant literature about spontaneous polarization, only a few attempts have been made to determine the rotational viscosity. We set up a model for the electric response of a ferroelectric liquid crystal cell on application of an electric field. For the application of a triangular wave voltage we derive a relation between the rotational viscosity, the spontaneous polarization, the tilt angle, the maximum induced polarization current and the electric field strength. Experiments are carried out on several ferroelectric liquid crystals and the derived relation was used to determine the rotational viscosity. The relation between the rotational viscosity and the polarization on the one hand and the optical switching time on the other hand is discussed in some detail.

ISSN:0267-8292    

DOI:10.1080/02678298808086395

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Experimental order parameters for a series of solutes withC2vandD2hsymmetry dissolved in the nematic liquid crystal comprised of 55 wt % 1132 (Merck ZLI 1132) and 45 wt% EBBA-d2(N-(4-ethoxybenzylidene)-2,6-dideutero-4-n-butylaniline) are obtained from N.M.R. measurements. In this mixture the average gradient in the electric field experienced by2H2is zero. The order parameters are calculated using a model based on short range repulsive interactions, which depend on the dimensions of the solute. The calculated values are in excellent agreement with the experimental results which suggests that these short range interactions are responsible for solute ordering in the 55wt% 1132/EBBA-d2system. It is also shown that in the two component liquid crystal solvents, 1132 and EBBA-d2, the interaction between the molecular quadrupole moment of the solute and the mean electric field gradient due to the liquid crystal plays an important role in determining the solute ordering.

ISSN:0267-8292    

DOI:10.1080/02678298808086396

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This paper presents measurements of spontaneous polarization made on two ester-bridged materials (SCE1 and CE8). The two materials are chosen to be representative of long pitch (SCE1) and short pitch (CE8) materials. The measurements were made by two different methods, Diamant bridge and field reversal; these methods are compared and the results shown to be in good agreement. The variation in results between different samples of these materials is discussed and the results compared (where possible) with the work of other authors. Special attention is paid to the variation which occurs between the published spontaneous polarization measurements of different authors. The reasons for this variation are examined and variation in sample alignment and the determination of the transition temperature by different authors are shown to be major causes.

ISSN:0267-8292    

DOI:10.1080/02678298808086397

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The effects of equibiaxial extensional flow on the structural state of a thermotropic liquid crystal aromatic copolyester are studied through wide-angle X-ray scattering (WAXS), strain recovery above the melting point, and differential scanning calorimetry (D.S.C.). For that purpose, samples were melted, stretched and cooled to room temperature. WAXS patterns and strain recovery show that equibiaxial extension (achieved through the lubricated squeezing experiment) results in a planarly-oriented state, i.e. preferred molecular orientation perpendicular to the compression direction accompanied by random molecular orientation within the plane of extension. This flow-induced oriented state may relax partially if not prevented by stretching in the super-cooled liquid state (10-30 K below the melting point). Quenching immediately after deformation at a high temperature can also result in the retention of a high degree of orientation, but it lowers the degree of crystallinity. D.S.C. data show that low cooling rates and large extensions lead to the highest crystallinity. Strain recovery upon reheating is remarkably high for samples with high orientation. This large recovery is attributed to the elasticity of the macrostructure which is formed by the LCP molecules (structural elasticity) and not to the elasticity of the molecules.

ISSN:0267-8292    

DOI:10.1080/02678298808086398

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

It is possible to untwist reversibly the helical superstructure of elastomers with cholesteric and chiral smectic C*phases by using strain. In that way a cholesteric structure can be transformed into a nematic structure and a chiral smectic C*into a smectic C structure. The latter case is especially interesting because a structure without a macroscopic polarization (chiral smectic C*) is transformed into one with a macroscopic polarization (smectic C like arrangement).

ISSN:0267-8292    

DOI:10.1080/02678298808086399

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0267-8292    

DOI:10.1080/02678298808086391

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor