Shoichi Kondo

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...

The Pair Intermolecular Interaction Energy of the Two Nematogenic Liquid Crystals

Abstract The dispersion term in the intermolecular potential calculated from the Rayleigh-Schrodinger perturbation theory exhibits the similar angle dependence as assumed by Maier-Saupe for the model system of MBBA.

Liquid crystalline properties and molecular packing of semifluorinated n-alkanes F(CF2)10(CH2)mH

The phase transitions for a homologous series of semifluorinated n-alkanes, F(CF 2 ) 10 (CH 2 ) m H, with 2 ≤ m ≤ 19 (FlOHm), have been characterized using a polarizing microscope, DSC, X-ray diffraction, and dilatometry. Thermal analysis and optical textures indicate the presence of the smectic-smectic phase transition when the number of methylene units ranges from 6 to 12. The phase-transition temperature depends on the length (m) of the hydrocarbon segment. The density decreases with increases in the carbon number of the hydrogen segment. The data for both the thermal properties and the density suggest that the smectic-smectic phase transition is significantly first-order, which is primarily caused by a change in the molecular packing for the molecular rearrangement, while a transition for the clearing point is related to disordering of the entire molecule. The volume jump shows that FlOHm have the same molecular packing in the high-temperature mesophase and that their magnitude is greater than that of the conventional liquid crystalline compounds having an aromatic-mesogenic core. The effects of the fluorinated segment for the phase transitions are also discussed herein.

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.

On the Even-Odd Effect of Volume Changes at I/N and N/SmA Transitions

Abstract The temperature dependences of specific volumes have been measured by dilatometer for N-(4-n-pentyloxybenzylidene)-4-n-alkylaniline, 50.n (from n = 4 to 14). The compounds with odd-numbered carbons in the alkyl chain exhibit larger volume changes than those with the next even-numbered carbons at the isotropic to nematic transition, whereas at the nematic to smectic A transition an opposite alternation is found in the magnitude of the volume change. The even-odd effect at the nematic-smectic A transition is attributed to the width in the nematic temperature range.

Dielectric behavior of semifluorinated n-alkane (F(CF2)n(CH2)mH). II

Abstract Dielectric measurements of diblock semiluorinated n-alkanes, (F(CF2)n(CH2)H), n=10, m=6−14., were carried out in the frequency range 20Hz to 106 Hz and in the temperature range from the waxy solid to isotropic state. Dielectric loss curves were observed only in the mesophase/liquid crystal state. The activation energies for the materials of m=6−9 were smaller than those of m=11 and 12. Single relaxation process can explain the observations in liquid crystalline phase. An alternation in the total integrated intensity, δϵ′ in the vicinity of phase transition temperature was found against even/odd number of carbon in alkyl group.