Shigeru Mita

Monte Carlo simulations using the dipolar Gay-Berne model: effect of terminal dipole moment on mesophase formation

Abstract The effects of dipole-dipole interaction on mesophase formation are investigated with a Monte Carlo simulation using the dipolar Gay-Berne potential. It is shown that the dipole moment at the end of a molecule causes a shift in the nematic-isotropic transition toward higher temperature and a spread of the temperature range of the nematic phase and that layer structures with various interdigitations are formed in the smectic phase.

Monte Carlo simulations on mesophase formation using dipolar Gay–Berne model

Abstract We report the results of a Monte Carlo simulation of polar particles interacting via the Gay-Berne potential combining dipole-dipole interactions. Simulations were carried out on a system of 256 particles with either a zero dipole moment or longitudinal dipole moment located at the centre of the molecule. The system was found to spontaneously form nematic, smectic and crystal phases from an isotropic phase with a random configuration as temperature was decreased, irrespective of values of the dipole moment. The results do not give any indication of a net polarization even in the system with a strong dipole moment (μ∗ = 2.00). The transition temperature from the isotropic to nematic phase is not sensitive to the value of the dipole moment within the limits of statistical error, while the transition from the nematic to smectic phase depends on the strength of dipole moment. At lower temperatures forming the smectic or the crystal phase, the translational order along the director increases with incr...

On the Phase Transition Behaviour of Binary Systems: Various Non-Nematic Solutes in Nematic Solvent (EBBA)

Abstract Phase transition behaviour of the systems of EBBA with methyl alcohol (MeOH), 1.2-dibromo-ethylene (DBE), o-xylene, m-xylene, and p-xylene has been studied. The phase diagrams for each system have been determined by the polarizing microscope. The slopes, βn and Bi, of the nematic and the isotropic phase boundary lines in each system have been qualitatively described by the molecular field treatment proposed by Humphries. The order parameters for both cis-and trans-DBE in EBBA have been obtained from analyses of 1H-NMR spectra. In the nematic phase, they decrease with increase in temperature. In the nematic/isotropic coexisting phase (N/I phase), the order parameter for CIS-DBE is almost independent of temperature. The proton spin-lattice relaxation times (T1) in the MeOH/EBBA system have been measured by a pulse NM R technique. Little temperature dependence of T1 has been found in the N/1 phase region.c

Influence of Longitudinal Dipole on Mesophase Formation via Computer Simulation

Abstract Monte Carlo simulations for the system composed of Gay-Berne molecules with a longitudinal dipole located near the end of the molecule have been undertaken. The system of 256 molecules of a prolate ellipsoidal shape with the dipole has been studied using the reaction field method for long-range dipolar interactions. It is found by the analysis of the microstructure that the molecules with the strong dipole form a tetragonal structure within a layer, while the nonpolar system similar to the central longitudinal dipolar system forms a hexagonal structure. The analysis of the microstructure in the nematic and isotropic phases has also been performed.

Birefringence study of the nematic-smectic A phase transition of N-(4-n-pentyloxybenzylidene)-4-n-alkylaniline (50.m)

Abstract The birefringence has been measured for the homologous series of N-(4-n-pentyloxybenzylidene)-4-n-alkylaniline (50.m) where m = 4 ∼ 8. An odd-even alternation of jumps in the birefringence at the nematic-smectic A transition temperatures is exhibited for the homologous series. The nematic-smectic A transitions are confirmed from the jumps to be of first-, second-, first-, very weakly first-, first-order, in going from 50.4 to 50.8. The transition order of these compounds is discussed in terms of the critical exponent of a Landau mean-field model.

Study on Molecular Polarizabilities of Cyclohexane Derivatives

Abstract The refractive indices and densities have been measured as a function of temperature for trans-4-alkylcyclohexyl 4′-n-pentyloxyphenylester and trans-4-alkylcyclohexyl 4′-cyanophenylester in the liquid crystalline and liquid phases. The molecular polarizabilities have been evaluated by Vuks’ formula. The polarizabilities obtained are compared with those estimated from bond polarizability calculations for the molecules. The relative nematic stabilities of the cyclohexane derivatives are discussed in terms of the molecular parameters measured.

Ab initio calculations of the charge densities in tricarbonyl(boat p-xylene)chromium complexes

Abstract Ab initio SCF calculations predict that the charge densities on the aryl carbons of Cr(boat p -xylene)(CO) 3 and also the difference in charge density from the free boat p -xylene are dependent on the degree of deformation of the boat. This prediction is consistent with the observed geometry-dependent 13 C NMR complexation shifts of Cr(paracyclophane)(CO) 3 complexes.

Characterization of (perfluorodecyl) n-alkanes, F(CF2)10(CH2)mH

Abstract A homologous series of semifluorinated n-alkanes, F (CF2)10(CH2) m H, with 2 ≤ m ≤ 19 has been synthesized and their properties characterized using a polarising microscope, differential scanning calorimetry and X-ray diffraction. The compounds of 6 ≤ m ≤ 12 exhibit the smectic B phase. The molecules from m = 13 to 19 show only a melting endotherm in the DSC traces. Conformational structured are discussed on the basis of ab initio calculations.

Structure Effect of Solute on Orientational Order in Binary Mixture by 2H-NMR and Molecular Simulations

Abstract The orientational order parameters of six solutes with different shapes and sizes dissolved in two nematic solvents have been measured as a function of temperature. The parameter, Sxx-Syy is correlated with the molecular geometrical structure, while Szz is affected by not only the geometry but also the anisotropy in the polarizability. The molecular dynamics simulations are carried out using a realistic atom-atom potential for evaluating the ordering properties in the nematic phase. The results provide reasonable values of Szz corresponding to experimental ones for solutes and solvents, and also a prediction of uniaxiality for the nematic phase.

Identification of transitions in lyotropic mesophases in hexaethylene glycol dodecyl ether–water by precision densimetry

The temperature dependence of the density has been measured for several concentrations of the hexaethylene glycol dodecyl ether (C12E6)–water (H2O) system, which exhibited lyotropic mesophases. The transitions from the lamellar (Lα) phase to the micellar solution (L1) phase and from the hexagonal (H1) phase to the micellar solution phase are of first order, and the molecular packing in the Lα phase is closer than that in the H1 phase. The mixture with 65.0 wt.% C12E6 exhibits L1, cubic (V1), H1 and Lα phases. The individual phase transitions between the H1, V1, Lα and L1, phases in sequence were clearly evident in the reduced density. The H1–V1 and V1–Lα phase transitions are of second order.