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The molecular packing and electronic transport characteristics of mesogenic phthalocyanines having alkyl side chains at non-peripheral sites, 1,4,8,11,15,18,22,25-octaalkylphthalocyanine and its fa... more...

Here we discuss requirements for high performance and solution processable organic semiconductors, by presenting a systematic investigation of 7-alkyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophenes (Ph-BTBT-C n ’s). We found that the solubility and thermal properties of Ph-BTBT-C n ’s depend systematically on the substituted alkyl-chain length n. The observed features are well understood in terms of the change of molecular packing motif with n: The compounds with n ≤ 4 do not form independent alkyl chain layers, whereas those with n ≥ 5 form isolated alkyl chain layers. The latter compounds afford a series of isomorphous bilayer-type crystal structures that form two-dimensional carrier transport layers within the crystals. We also show that the Ph-BTBT-C10 afford high performance single-crystalline field-effect transistors the mobility of which reaches as high as 15.9 cm2/Vs. These results demonstrate a crucial role of the substituted alkyl chain length for obtaining high performance organic semiconductors and field-effect transistors. more...

The origin of the negative temperature dependence of carrier mobility in a crystal phase of 1,4,8,11,15,18,22,25-octahexylphthalocyanine was studied by utilizing a charge transport simulation based on Marcus theory and density functional theory. In order to understand the unique negative temperature dependence of carrier mobility, the theoretical calculation was carried out by taking the thermal expansion of the lattice parameters into consideration. The calculated hole mobility exhibited the similar temperature dependence as the experimental results. In the electron mobility calculation, the negative temperature dependence could be simulated by considering the degeneracy of lowest unoccupied molecular orbitals as well as the thermal expansion. more...

We experimentally examined the surface nematic bistability of a liquid crystal cell with four kinds of photoalignment micropatterns, including stripe, herringbone, random dots and random lamella. We checked a necessary condition on the pattern symmetry required for the bistability. The optical properties of the stripe pattern cells were compared with those of the conventional chequer pattern cells, and the effects of the pattern geometry on the optical properties were discussed. Inspired by the results of the random lamella patterns, we proposed a novel and practical method of fabricating large-area bistable patterns. more...

Molecular dynamics simulations were done for a chiral liquid crystalline (LC) monolayer with and without transmonolayer H 2 gas flow. The rotational dynamics of the monolayer LC molecule (MHPOBC) along its long-molecular axis was analyzed by tracing the orientations of the C = O bond close to the chiral part. We found that the reorientational motion along the molecular long-axis within the simulated time scale (10ns) was mostly not rotation but libration. We also found that the transmonolayer H 2 gas flow renders no apparent effects on the rotational motions of the MHPOBC molecules. Dependency of the MHPOBC rotational directions under the gas flow on the molecular chirality was not seen either. In contrast, marked chirality dependency was found in the asymmetry of the C = O orientational distributions that are oppositely biased each other between (S)- and (R)-MHPOBC. Resultant net polarization directions from these biased C = O distributions correspond to the experimentally reported spontaneous polarizati... more...

We present the results of our investigations on the electro‐optic response of the cubic phase liquid crystal compounds 1,2‐bis‐[4‐n‐octyloxy‐benzoyl]‐hydrazine (BABH8) and 4’‐n‐hexadecyloxy‐3’‐nitrobiphenyl‐4‐carboxylic acid (ANBC16) in Kerr cell geometry. The AC electric field response in the BABH8 cubic phase was found to be as small as that of the isotropic phase, even though there was a response in the adjacent smectic C (SmC) phase. The response in the SmC phase means that the BABH8 molecule itself has an electric field coupling ability, but this ability is strongly inactivated in the cubic phase. This inactivity to the AC fields was also found in the cubic phase of ANBC16. This behaviour could be explained by the small structural unit size of the cubic phase. more...

Orientational bistability of the nematic liquid crystal occurs on the frustrated surface alignment of checkerboard. Macroscopic orientational switching takes place between two states by an appropriate in-plane electric field. The threshold electric fields decreased in both switching directions as temperature increased. The focused laser light could heat up only the selected region in the cell including a light-absorbing medium. Irradiating the laser concurrently with an appropriate electric field, we switched the selected regions in the alignment pattern. The switched region was stable without the disturbance from the exterior. Extending this process, we realized extremely fine bistable devices. Here we mention some issues like the switching domains and the relation between the threshold electric filed and temperature. more...

We investigate numerically the configuration of a nematic liquid crystal around two spherical particles. For the description of the orientational order of a nematic liquid crystal, we adopt a Landau-de Gennes continuum theory in terms of a second-rank tensor order parameter Q(ij) together with the use of bispherical coordinates to describe the geometry of the system with two spherical particles. Above but close to the nematic-isotropic transition point, we observe capillary condensation of a nematic liquid crystal between the two particles under appropriate conditions. Below the transition point where liquid crystals possess nematic order, a point-like defect called a hyperbolic hedgehog appears close to a particle when strong normal anchoring is imposed. With the aid of an adaptive mesh refinement scheme to achieve sufficient numerical resolution to describe topological defects, we present our numerical results showing how the orientation profile of a nematic liquid crystal is distorted when the distance between two particles is small enough. more...

We present the results of our numerical calculations that focus on the dynamics of a nematic liquid crystal around a spherical particle imposing strong homeotropic anchoring at the surface. The first part of this article is devoted to the discussion of the effect of an external magnetic or electric field on the director configuration of a nematic liquid crystal. With the aid of an adaptive mesh refinement scheme, together with the tensor description of the orientational order, for the first time in numerical calculations we successfully reproduce the transition from a hyperbolic hedgehog defect to a Saturn ring defect, which was observed in a recent experiment. We also find that the trajectories of the defect core sensitively depend on the field strength. In the second part we investigate how a hydrodynamic flow influences the orientational order of a nematic liquid crystal around a particle carrying a hyperbolic hedgehog defect. We observe that for an intermediate Ericksen number, which characterizes the ratio of the viscous force to the elastic force of a nematic liquid crystal, the liquid crystal is strongly convected by the flow, which results in a considerable elastic distortion. more...

We perform molecular dynamics simulations using a simple model system of liquid crystal substance on air-water interface. A system of soft spherocylinders, which do not show smectic C phase in bulk, exhibits a tilted smectic phase when interacting with a model water plane. We observe not only macroscopic properties such as the pressure-surface area curve, but also correlation functions and diffusions as well. more...

Molecular dynamics simulations were done for terminally alkyl and alkoxy substituted azobenzene liquid crystal (LC) molecules at an air-water interface using realistic (LC and water) molecular models. The simulation result were compared with those of a corresponding amphiphilic modification, i.e. terminal ω-carboxyalkoxy substituted azobenzene. Comparison with a LC with a different mesogen core, phenylpyrimidine, was also made. The interaction energetics were found to be more or less similar both in the alkyl and alkoxy terminated azobenzene and its amphiphilic modification, i.e. cohesive energy dominated over adhesive energy. In contrast, a large difference was found between alkyl and alkoxy terminated azobenzene and phenylpyrimidine LCs; cohesive and adhesive energy contributions were competitive in the latter molecule. more...

By introducing an anisotropic factor in the cell dynamics of constant pressure molecular dynamics simulations, we dramatically reduce the artifacts related to cell shapes and overcome the difficulties of simulating anisotropic molecules under hydrostatic pressure. The method is especially effective for anisotropic liquids, such as smectic liquid crystals and membranes, however it can also be used for crystals and isotropic liquid as well. Crystal-smectic-nematicisotropic phase transitions in systems of soft spherocylinders are observed. more...

We investigate numerically the orientational configuration of a nematic liquid crystal around a spherical particle. The use of adaptive mesh refinement scheme proves quite useful to overcome the numerical difficulty arising from large scale difference between a particle and a topological defect. Our scheme reproduces successfully the hedgehog and the Saturn ring configurations that have been observed experimentally. To demonstrate that dynamical behaviors can also be investigated using our scheme, we present a simulation result which exhibits a transition from a hedgehog to a Saturn ring under the application of an external field. more...

A bistability of nematic liquid crystals was devised on the pattern of checkerboard-like local rubbing; the alignment of the liquid crystal on neighboring domains was orthogonal each other. 4-fold symmetry of the pattern and liquid crystal frustration forced bulk director to orient along one of two average directions of the local rubbings. A liquid crystal orientation was switched to the other by in-plane electric field. To realize bi-directional switching it was needed to apply electric field along two different directions using two pairs of electrodes. In this experiment we used a liquid crystal, which changes the sign of dielectric anisotropy to frequency of electric field. It has a merit of reducing number of electrodes into two, meaning simple electrodes structure. We successfully switched between two orientations with changing frequency of applying field. more...

Ferroelectricity is desirable for realizing fast-response liquid crystal devices. Existing ferroelectric liquid crystals are improper with the spontaneous polarization Ps being indirectly induced by the broken centrosymmetry of molecular arrangement. We found that Langmuir monolayers of certain dialkylated nematic compound exhibit a laterally polarized two-dimensional ferroelectric nematic. The Ps is comparable to that of chiral smectic liquid crystals, and shows a fast linear electro-optic switching with a microsecond response. Estimates of electrostatic energy suggest that the ferroelectricity may be driven by the direct dipolar interactions. more...

In this paper, we present a multi-stable property in a bimesogenic cholesteric liquid crystal material with a proper chiral additive and check its potential as an energy saving transmissive type liquid crystal display (LCD) through its electro-optic characteristics. Experimental results show that the multi-stable characteristics in the fabricated cholesteric LC cell are very stable. Such multi-stable properties depend on the driving frequency, voltage, and field direction. The contrast ratio in the fabricated transmissive type cholesteric LC cell was 15:1, which is a result produced by voltage and frequency control. more...

Monolayer structures of a chiral mesogen, (R)- or (S)-[4′-(1-methylheptyloxy)-3′-nitrobipheny1-4yl] 4-(trans-5-decenyloxy) benzoate, adsorbed on graphite were investigated with molecular dynamics simulations to clarify the mechanism of chiral supermolecular structure formation. We proposed a mechanism model that is based on the coupling between up-down symmetry breaking and the molecular tilt direction symmetry breaking of the monolayer. more...

This article compares switching behaviors between negative (Nn) and positive (Np) dielectro-anisotropic nematic liquid crystals driven by an in-plane electric field which is generated with interdigital electrodes. Even for Np type liquid crystals, excellent viewing angle characteristics were obtained as expected. Theoretical descriptions of the switching principle, i.e., threshold behavior and response mechanism, could be applied to both the Nn and Np type liquid crystals. However, the orientational deformation of the Np type liquid crystals caused by a distorted electric field which occurred near the edges of electrodes was not the same as that of the Nn type liquid crystals. The switching of the Np type liquid crystals near the edges of the electrodes by this field was followed by the in-plane switching of the liquid crystals between the electrodes. This remarkably distinctive dynamical behavior implied a difference in the response of the longitudinal axes for Nn and Np type liquid crystal molecules. The longitudinal axes of the latter seemed to be sensitive to the electric field component perpendicular to the substrates when applying the in-plane electric field. Furthermore, these experimentally obtained results were supported by computer simulations which analyzed the liquid crystal director distribution and transmittance pattern from edge-to-edge of a pair of electrodes when applying the in-plane electric field. more...

Molecular dynamics simulations have been used to study shear friction in Langmuir−Blodgett monolayers of carboxylic acids. The effects of partial fluorination of hydrocarboxylic acids, of introduct... more...

Effects of polymer surface structures on surface alignment of liquid crystal molecules were studied by comparison with our previous results of molecular dynamics simulations. An adsorption-related liquid crystal molecule alignment on the packed polyimide surface was found in the simulation study. In this article, we first compared the alignment on a sparse polyimide surface with the previous results of the packed polyimide surface to see effects of polymer surface density. The excluded volume effect with the polyimide domain edges additionally contributed to alignment of the liquid crystal molecules on the sparse surface, and resulted in a similar alignment structure (i.e. alignment direction and tilt angle) to the packed cases. Secondly, we made similar simulations by changing the polymer from a polyimide to a polyamide with similar polymer chain density. Differences between the corresponding packed polyimide case were found mainly in the energetics (the polyamide had about two thirds of the ads... more...

Preliminary results are presented on the molecular dynamics simulations of alignment of the liquid crystal molecule, 4-n-octyl-4′-cyanobiphenyl (8CB), on a polyimide (pyromelltic dianhydride-p-phenylene diamine) oligomer monolayer. We actually simulated a three-layer system, i.e., liquid crystal molecule/polyimide oligomer/a basal plane of graphite. First, simulations of the oligomers adsorbed on graphite were done in order to obtain reasonable adsorption structures, as the pre-stage simulation of the three-layer system. Then, by placing a liquid crystal layer on top, the three-layer system was simulated. The stable liquid crystal alignment direction on the polyimide monolayer was found roughly to be the polyimide chain direction with zero pretilt in this combination of liquid crystal and polymer materials. The calculated adsorption energy of an 8CB molecule to the polyimide monolayer was 128 kJ mol−1 and the carbonyl group of the polyimide was the main adsorption site. more...

A parallel algorithm for molecular dynamics simulations of polyatomic molecular systems is presented. The algorithm is optimized for shared-memory multiple processor computers by assigning each molecule to be a parallelization unit which is usually taken for each atom or interaction pair. A method to distribute all interaction pairs to each molecule in almost equal numbers is described. The algorithm is tested by simulation of a liquid crystal molecule system on four-and eight-processor workstations. Overall speedups of 3.6 and 5.7 are obtained on four-and eight- processors, respectively. A non-iterative algorithm to constrain bond-length degrees of freedom is also tested with regard to its efficiency for parallel computation. A performance superior to that of the iterative SHAKE algorithm was obtained more...

Model adsorption structures of polyamide (poly(e-caprolactam)) on graphite surfaces which have been proposed from a scanning tunneling microscopy (STM) study were examined by molecular dynamics (MD) simulations using a short oligomer as a model molecule. The model structure for loose chain packing was thermodynamically (and locally) stable in the simulation, whereas that for close chain packing was unstable. Moreover, the former structure was globally unstable to a finite size (chain spacing) disturbance, and a transition to the structure with a different chain alignment direction on the graphite surface occurred. As a result, in contrast with the STM study, the simulation results suggested this structure with a 0.47-nm chain spacing and chain directions of the (1120) direction of the graphite surfaces as the most probable absorption structure. Possible reasons for this contradiction were discussed. For the close chain packing structure, no model structure could be obtained from the simulations. more...

Preliminary results are presented on molecular dynamics simulations of the alignment of 8CB (4-n-octyl-4′-cyanobiphenyl) liquid crystal molecules on a graphite surface. Their stable alignment direction was found to be the direction of the basal plane of graphite. The calculated adsorption energy of an 8CB molecule was 151·5 kJ mol −1 and its alkyl chain was the main adsorption portion. Molecular dynamics simulation could therefore be an effective probe to the surface-induced alignment mechanism of liquid crystal molecules. more...

The four-fold symmetry of a checkerboard-like surface alignment consisted of square domains arrived at the macroscopic orientational bistability of nematic liquid crystals. Switching between the two orientations took place with an appropriate electric field. Here the threshold field of bistable switching decreased as temperature increased, and the light could heat only the selected region in the cell including a light-absorbing medium. Irradiating the laser concurrently with an electric field, we addressed a selected region in the alignment pattern without the disturbance of neighboring regions. Extending this process, we realized an extremely fine bistable device of nematic liquid crystal with a pixel size down to about 2 μm. more...

A non-iterative version of the matrix method which can be easily vectorised and parallelized is presented. The original matrix method, which is conceptually identical to the familiar SHAKE algorithm, is shown to be non-iterative when incorporated with the Verlet and leap-frog integration schemes with the same constraint error order as the (local) error order of the accompanying integration schemes. The method is checked by test simulations with n-butane and the liquid crystal moleculae 5CB (4-n-pentyl-4′-cyanobiphenyl) in which its effectiveness is demonstrated. more...

An effective anchoring model for the patterned surface with bidirectional rubbing by atomic force microscope was proposed. The model was a simple additive function of two bidirectional anchoring contributions of the patterned surface, with consideration of higher-order terms of the anchoring function. The bistable switching behavior of the nematic liquid crystal cells with the patterned surface was investigated analytically and numerically using this anchoring model. more...

We demonstrate a robust in-plane bistability of liquid-crystal surface alignment based on tailored submicrometer-sized surface domains imposing a frustrated alignment. By a nanorubbing technique utilizing the atomic force microscope, we prepared an orientational checkerboard pattern on polyimide layer, consisting of square unit domains on which the alignment is locally constrained to be planar yet orthogonal between the neighboring domains. Due to the four-fold rotational symmetry of the pattern, the two diagonal axes of the square domain become equally stable directions for the macroscopic liquid crystal alignment. The alignment could be switched between these two states by an in-plane electric field above a certain threshold, determined by the local azimuthal anchoring. more...

Entropy and heat capacity are calculated in phase sequence of crystal, hexatic smectic- B , and smectic- A liquid crystals through constant pressure and temperature molecular-dynamics simulations of parallel soft spherocylinders. The transition from crystal to hexatic smectic- B phase is continuous while the transition to smectic- A phase is first order. The dependence of the phase sequence against the molecular shape anisotropy is investigated and there exists a triple point at a rather small anisotropy. Hopping diffusion of molecules is observed in the hexatic smectic- B phase. more...

We investigate numerically static and dynamic properties of cholesteric blue phases. Our study is based on a Landau--de Gennes theory describing the orientational order of a liquid crystal in terms of a second-rank tensor. To find the shape and size of the unit cell conforming to the minimum of the free energy, we let the geometrical parameters characterizing the unit cell relax in the course of the time evolution via a simple relaxational equation. We investigate the effect of an electric field on the structure of cholesteric blue phases. We study how the deformation of the unit cell in response to the electric field $\mathbit{E}$ depends on the strength and direction of the electric field and the original structure of cholesteric blue phases. Our results qualitatively agree with the experimental findings. Although in a weak field, the strain tensor is proportional to ${E}^{2}$ as previously argued, for a moderate field the distortion is no longer proportional to ${E}^{2}$ and can be even nonmonotonic with respect to ${E}^{2}$. Furthermore, we investigate the kinetic processes of the deformation, rearrangement, and extinction of disclination lines under a strong electric field. We show that the kinetics of disclination lines is highly complicated and sensitively depends on the initial structure of blue phases, the direction of the electric field, and the sign of dielectric anisotropy ${ϵ}_{\text{a}}$. In most cases, a strong field aligns the liquid crystals in a uniform (positive ${ϵ}_{\text{a}}$) or helical (negative ${ϵ}_{\text{a}}$) manner without disclination lines. However, for negative ${ϵ}_{\text{a}}$ and the direction of the electric field parallel to the body diagonal of the unit cell, disclination lines do not disappear and form a two-dimensional hexagonal lattice. more...

We evaluate the azimuthal anchoring energy of a grooved surface by calculating numerically the Frank elastic energy of a nematic cell composed of the grooved surface and a flat one with rigid azimuthal anchoring, where the director is fixed along the $\ensuremath{\phi}$ direction. We pay attention to the surface anchoring induced by elastic distortions of the director due to its contact with a nonflat surface, which impose local planar degenerate anchoring. Surface anchoring of this kind was analyzed analytically for shallow grooves by Berreman [Phys. Rev. Lett. 28, 1683 (1972)] and critically reexamined by the present authors [Phys. Rev. Lett. 98, 187803; 99, 139902(E) (2007)]. We consider two types of surface. one is a surface with one-dimensional sinusoidal parallel grooves, and the other is a surface with two-dimensional square patterns whose surface height is given by a sum of two sinusoidal functions with orthogonal wave vectors. The total energy is the sum of the anchoring energy and the twist energy in the bulk. For the calculation of the twist energy to be eliminated and the evaluation of the azimuthal-angle dependence of the anchoring energy, the ``average'' azimuthal angle at the bottom, $\ensuremath{\varphi}(0)$, must be determined. We adopt two methods to determine $\ensuremath{\varphi}(0)$. One is a simple extrapolation of the twist deformation in the bulk. The other relates $\ensuremath{\varphi}(0)$ to the variation of the total Frank elastic energy with respect to $\ensuremath{\phi}$. Our calculations indicate that both methods give essentially the same results, which indicates the consistency of those two methods. We also show that, for a surface with square patterns, the agreement between theory and numerical calculations is quite good even when the maximum of the surface slope is around 0.4, which theory assumes is much smaller than unity. When the surface slope is of order unity, the deviation of numerical results from theory crucially depends on the the surface elastic constant ${K}_{24}$. more...

To examine the anchoring energy of a surface with one-dimensional grooves of sinusoidal shape, we carry out numerical calculation of the Frank elastic energy of a nematic cell composed of such a grooved surface and a flat surface. We evaluate the anchoring energy of the grooved surface by carefully eliminating the contribution from a uniform twist deformation in the bulk. When $qA\ensuremath{\lesssim}0.2$, with $q$ and $A$ being the wave number and the amplitude of the surface groove, we find that the azimuthal-angle dependence of the calculated anchoring energy agrees perfectly with our previous analytical result under the assumption of $qA⪡1$ [Fukuda et al., Phys. Rev. Lett. 98, 187803 (2007); 99, 139902(E) (2007)]. Even when $qA\ensuremath{\simeq}0.6$ or 1, we observe an unexpectedly good agreement between the calculated and the analytical anchoring energies, indicating the wide applicability of the analytical anchoring energy in spite of the assumption of $qA⪡1$ in its derivation. more...

We investigate analytically the anchoring of a nematic liquid crystal on a two-dimensionally grooved surface of arbitrary shape, induced by the elastic distortions of a liquid crystal adjacent to the surface. Our theoretical framework applied to a surface with square grooves reveals that such a surface can exhibit bistable anchoring, while a direct extension of a well-known theory of Berreman [Phys. Rev. Lett. 28, 1683 (1972)] results in no azimuthal anchoring in the so-called one-constant case (K1=K2=K3, with K1, K2, and K3 being the splay, twist, and bend elastic constants, respectively). We show under the assumption of K1=K2=K that the direction of the bistable easy axes and the anchoring strength crucially depend on the ratios K3/K and K24/K, where K24 is the saddle-splay surface elastic constant. To demonstrate the applicability of our theory to general cases and to elucidate the effect of surface shape and the elastic constants on the properties of surface anchoring, we also consider several specific cases of interest; one-dimensional grooves of arbitrary shape, rhombic grooves, and surfaces possessing 2N -fold symmetry, including hexagonal grooves, and show the following: (i) The rescaled anchoring energy f(phi)/f(pi/2) of one-dimensional grooves, with phi being the angle between the director n and the groove direction, is independent of the groove shape. (ii) Whether two diagonal axes of rhombic grooves can become easy axes depends sensitively on K3/K, K24/K and the angle alpha between the grooves. The angle alpha yielding the maximum anchoring strength for given groove pitch and amplitude depends again on K3/K and K24/K; in some cases alpha=0 (one-dimensional grooves), and in other cases alpha not equal 0, gives the maximum anchoring strength. Square grooves (alpha=pi/2) do not necessarily exhibit the largest anchoring strength. (iii) A surface possessing 2N -fold symmetry can yield N -stable azimuthal anchoring. However, when K1=K2=K3 and N>or=3, azimuthal anchoring is totally absent irrespective of the value of K24. The direction of the easy axes depends on K3/K, K24/K, and whether N is even or odd. more...

To account for azimuthal surface anchoring of a nematic liquid crystal, Berreman [Phys. Rev. Lett. 28, 1683 (1972)] proposed a simple model attributing the surface anchoring to the elastic distortion of the liquid crystal induced by the grooves of a surface. He showed that the surface anchoring energy is proportional to ${sin }^{2}\ensuremath{\phi}$, with $\ensuremath{\phi}$ being the angle between the director at infinity and the direction of the surface grooves. We argue that his assumption of negligibly small azimuthal distortion of the nematic is not valid. Proper treatment of the azimuthal distortion reveals that the Berreman's model should yield a surface anchoring energy proportional to ${sin }^{4}\ensuremath{\phi}$. This implies that surface grooves alone cannot contribute to the surface anchoring coefficient in the usual Rapini-Papoular sense. more...

Methods of molecular dynamics simulations for anisotropic molecules are presented. The new methods, with an anisotropic factor in the cell dynamics, dramatically reduce the artifacts related to cell shapes and overcome the difficulties of simulating anisotropic molecules under constant hydrostatic pressure or constant volume. The methods are especially effective for anisotropic liquids, such as smectic liquid crystals and membranes, of which the stacks of layers are compressible (elastic in direction perpendicular to the layers) while the layer itself is liquid and only elastic under uniform compressive force. The methods can also be used for crystals and isotropic liquids as well. more...

We present the results of our numerical attempts to simulate the configuration of a nematic liquid crystal around a spherical particle. We focus on the effect of an external field, such as a magnetic field or a flow field, on the director configuration and the topological defects accompanied by the particles. The use of adaptive mesh refinement together with a tensor order parameter for the description of the orientational order makes it feasible to tract the dynamics of a nematic liquid crystal without any special treatment of the topological defects. more...

We investigate numerically the structure of topological defects close to a spherical particle immersed in a uniformly aligned nematic liquid crystal. To this end we have implemented an adaptive mesh refinement scheme in an axi-symmetric three-dimensional system, which makes it feasible to take into account properly the large length scale difference between the particle and the topological defects. The adaptive mesh refinement scheme proves to be quite efficient and useful in the investigation of not only the macroscopic properties such as the defect position but also the fine structure of defects. It can be shown that a hyperbolic hedgehog that accompanies a particle with strong homeotropic anchoring takes the structure of a ring. more...

We investigate the azimuthal dependence of the switching field strength for nematic liquid crystal bistability on patterned alignment layers to determine the validity of a switching theory proposed by Kim et al. [Appl. Phys. Lett. 78, 3055 (2001)] and to evaluate higher-order azimuthal anchoring coefficients. Director behavior during switching is described in detail for general azimuthal directions of an applied electric field and the experimental results are explained on the basis of the theory. We obtain azimuthal anchoring coefficients up to the second higher-order term in an expansion of the anchoring energy function. Detailed analysis of the director behavior reveals a close analogy between the proposed model of nematic liquid crystal bistability and a coherent rotation (Stoner-Wohlfarth) model of ferromagnetism. This suggests a reversal-asymmetric property of the substrate-nematic interface director, differing from the reversal symmetry of the bulk nematic director, as far as the nematic bistability switching is concerned. more...

Hexatic smectic B liquid crystal (HexB) is studied by molecular dynamics simulations for a wide range of temperatures. In addition to the thermodynamic equilibrium HexB phase, there exist multiple metastable states with a smaller sixfold bond orientational order C 6 than the thermodynamic equilibrium phase. The values of C 6 are discrete, with each metastable state having different thermodynamic characteristics. 12- and 18-fold bond orientational orders C 6 n ( n = 2, 3) satisfy the scaling relation C 6 n = C 6 σ n for a wide range. The metastable HexB states are nested and each layer also has a discrete value of bond order forming these discrete states as a whole. more...

In this paper, we present electro-optic characteristics in cholesteric phase of the bimesogenic material with the helical twist power [HTP] agent BDH1218. The cholesteric phase of such mixture is more stable than blue phase and frequency-dependent in its alternative-current electric field response. It shows multi-stable-like domain structure characterized by the frequency and voltage applied. There are two driving methods for operation as a display. One is changing voltage under each of high and low frequency. The other is changing frequencies under a high voltage. We consider that the electro-optic characteristics of this cholecteric phase could be applied to electro-optic storage devices since all obtained gray levels are realized as memory states. more...

The higher-order component in liquid crystal (LC) surface free energy beyond the Rapini–Papoular anchoring potential was examined for azimuthal anchoring by analyzing nematic LC alignment on nanogrooved surfaces treated by rubbing or photoalignment. We confirmed that the surface anchoring energy for large director deviations cannot be properly described with the Rapini–Papoular form and should include higher order contributions in a power series of sin2 ϕ, as ∑n=12Wn sin2n ϕ, with ϕ being the azimuthal angular deviation. Based on the corrected Berreman’s theory, we obtained the anchoring ratio between the first and second order terms, W2/W1≈−1/4, and the surface elastic constant, K24≈−0.846K22, for 4-n-pentyl-4′-cyanobiphenyl. more...

The azimuthal nematic bistability was realized by frustration between two azimuthally orthogonal anchoring axes induced by a nanoimprinted groove pattern and mechanical rubbing. The nematic bistability can be explained by the revised Berreman model of groove-induced surface anchoring, recently introduced by Fukuda et al. [Phys. Rev. Lett. 98, 187803 (2007)]. The azimuthal bistability can be tuned in arbitrary direction by changing the groove pitch and rubbing conditions. This simple combinatorial scheme may be considered as a practical candidate for bistable displays with tailored bistable directions required in various liquid crystal device modes. more...

We study numerically the interaction between particles in a nematic liquid crystal mediated by its elastic distortions with the aid of the Landau-de Gennes continuum theory. We consider the cases where two particles impose rigid normal anchoring on their surfaces and are accompanied by a hyperbolic hedgehog defect. As a function of the distance between the centers of the particles D, we evaluate the force f acting on the particles by integrating the stress tensor. The result is well described by a power law f ∝ D −x . When the “dipoles”, composed of a particle and a hyperbolic hedgehog, are in parallel directions, the interaction is attractive and the exponent is x ≃ 4, consistent with the experimental observations together with the theoretical expectation of the dipole-dipole interaction. For antiparallel dipoles, repulsive interaction is observed and x ≃ 3.6, slightly stronger than the dipole-dipole interaction. more...

We study the effect of a hydrodynamic flow on the orientational configuration of a nematic liquid crystal around a spherical particle imposing rigid normal anchoring. We discuss the cases of large Ericksen numbers (characterizing the ratio of viscous force to the elastic force), where strong elastic deformation by the flow is expected. We assume the Stokes flow profile and deal with a simplified dynamic equation of the orientational order parameter of a second-rank tensor Q αβ. We consider the cases where a particle accompanying a hyperbolic hedgehog or a Saturn ring is subjected to a flow along the axis of rotational symmetry. In both cases the orientation profiles exhibit considerable deformation by a flow. more...

The alignment of the liquid crystal on the alignment layer is determined by the anchoring energy and the elastic energy. In the case of uniform alignment, the anchoring energy generally overwhelms the elastic energy to make an uniform alignment over all the area. But the behavior of the liquid crystal on artificially designed multi-domains system with competing directions of easy axis can be different. The competition between two factors is expected to force the system to stabilize in the balanced configuration that could be different from which is induced microscopically by the anchoring energy. We used an atomic force microscopy (AFM) to create micron and nanometer size multi-domains with two alignment directions. With changing the domain size, we observed a variety of different behavior of the liquid crystal texture. more...

Viewing angle characteristics were systematically obtained when using in-plane switching (IPS) of liquid crystals. Although the IPS mode originally shows stable electro-optical performance regardless of viewing directions, the viewing angle characteristics are found to be strongly dependent on pretilt angle (slant angle of the liquid crystals from the substrate). Experimentally, the smaller the pretilt angle of the liquid crystal, the much wider the viewing angle characteristics, while larger pretilt angles of liquid crystals cause the characteristics to deteriorate. This deterioration occurs in a particular viewing direction, i.e. at right angles to the initial orientation direction of the liquid crystal when there is no in-plane electric field. The experimentally observed behaviour of the viewing angle dependence on the pretilt angle was also confirmed by computer simulations. Calculated iso-contrast contour lines, as a function of the pretilt angles, nearly coincide with the experimentally obtained vie... more...