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International audience; Stochastic resonance is a noise phenomenon that benefits applications such as pattern formation, neural systems, microelectromechanical systems, and image processing. This study experimentally clarifies that the orientation of the liquid crystal molecules was switched between two stable positions when stochastic resonance was induced by colored noises in a liquid crystal light valve with optical feedback. Ornstein-Uhlenbeck and dichotomous noises were used for colored noise, and the noise was applied to the drive voltage of the liquid crystal light valve. The signal-to-noise ratio was measured with respect to changes in the noise type, noise intensity, and autocorrelation time of the noise. It was found that typical stochastic resonance was observed with a noise autocorrelation time of approximately 20 ms or more for both noise types, and dichotomous noise further enhanced the stochastic resonance compared to the Ornstein-Uhlenbeck noise. This suggests that it is possible to maximize stochastic resonance in a liquid crystal light valve by optimizing the conditions of colored noise.

Utilization of the self-organizing nature of soft materials is promising for fabricating micro- and nano-structures, which can be applied for optics. Because of the high birefringence, liquid crystals are especially suitable for optoelectronic applications such as beam steering and polarization conversion. On the other hand, most self-organized patterns in liquid crystals are one-dimensional and there are only a few examples of two dimensional systems. Here we study the light diffraction from a micro-pixelated pattern of a nematic liquid crystal which is formed by self-organization of topological defects. We demonstrate that the system works as a tunable two dimensional optical grating, which splits the incident laser beam and changes the polarization property. The intensity can be controlled by electrical voltages, which cause extinction of the zeroth-order beam. The polarization properties depend on the location of spots. The numerical calculation and the theoretical analysis not only support the experimental results but also unveil the uniqueness of the pixelated structure.

Three-dimensional observation of Brownian particles under shear flow is performed with a stereo microscope to examine the nature of the Brownian motion that occurs in the presence of shear flow. From the three-dimensional trajectories of the particles, we clearly demonstrate the occurrence of anomalous diffusion in the flow direction and the coupling of the displacements in the flow and velocity gradient directions. Furthermore, we experimentally obtain the probability distribution function and current density, which also exhibit characteristic features, and compare the obtained results with theoretical results derived using the Fokker-Planck equation.

Electrokinetics of small particles immersed in anisotropic fluids is attracting attention in recent years. Here we focus on microscopic appearance of single as well as self-assembled particles moving in the electrohydrodynamic convection (EHC) of a nematic liquid crystal with low birefringence. Characterisation of the birefringent properties is made by polarised light microscopy under different illumination conditions. Because of the small optical anisotropy, the director distortion around the particles clearly exhibits distinctive colours on both sides depending on the height in the cell. The observation can be explained as the change in the net phase retardation of the light. It is also found that a caterpillar-like motion is possible by tuning temperature, although the horizontal size of the EHC rolls is relatively narrow.

We have theoretically investigated the electrorheological effect in a dual-frequency liquid crystal, in which the dielectric anisotropy depends on the frequency of an applied ac electric field. In ...

The Freedericksz transition was investigated in a dual-frequency liquid crystal consisting of a mixture of 2-chloro-4-(4-pentylbenzoyloxy)benzoate and N-(4-methoxybenzylidene)-4-butylaniline, in which dielectric anisotropy strongly depends on the frequency of the applied ac electric field. Because the threshold voltage for the transition from an undistorted state of orientation to a distorted one is a function of the dielectric anisotropy and of the Frank elastic constants, the threshold voltage was expected to depend on the frequency. The threshold voltage increased steeply as the frequency approached the crossover frequency at which the dielectric anisotropy vanished and the threshold voltage eventually diverged. Furthermore, we examined the Freedericksz transition under ac voltages of two different frequencies.

Recently, we reported the discovery of enormous negative viscosity of a nematic liquid crystal in the presence of turbulence induced by ac electric fields, which enabled us to observe unique phenomena related to the negative viscosity, such as spontaneous shear flow, hysteresis in flow curves, and self-oscillation [Orihara et al., Phys. Rev. E 99, 012701 (2019)10.1103/PhysRevE.99.012701]. In the present paper, we report the rheological properties of another nematic liquid crystal, which is a homologue of the previous one. The properties of the present liquid crystal are strongly dependent on electrical conductivity. Three samples with different conductivities were prepared by changing the amount of an ionic dopant. It was found that the lowest-conductivity sample without dopant shows no negative viscosity whereas the other ion-doped samples exhibit negative viscosity with strong dependence on the frequency of the ac electric field, consistent with microscopic observations. Phase diagrams of the negative- and positive-viscosity states in the amplitude and frequency plane are constructed to show the conductivity effect. Furthermore, we propose a model to reproduce another type of self-oscillation found in the present study.

$O\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ $v\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}s$ (corkscrews of light spinning about zeros in the electric field) offer many applications in $e.g.$ optical communication, superresolution microscopy, and astronomical imaging, so creating them controllably is of considerable interest. The authors reveal that an electric-field-induced, self-assembled grid of topological defects can generate optical vortices at different length scales, via two mechanisms: directly by transmission through an individual defect, and by diffraction from a dislocation in the grid pattern. The efficiency of generating optical vortices here can approach 100%, even for different wavelengths of light, and can be tuned by an applied voltage.

We report on the discovery of enormous negative viscosity in a nematic liquid crystal in the presence of turbulence induced by electric fields. As the negative viscosity in this system is so large, we are able to observe several phenomena originating from it. For example, we observe a spontaneous shear flow that rotates the upper disk of a rheometer, as well as the reversal of the rotational direction upon applying an external torque in the opposite direction. Hysteresis loops are also observed in the shear-stress--shear-rate curves, which is reminiscent of those seen for ferromagnetic and ferroelectric materials. The similarities between the phenomena observed for our system and ferroic materials are comprehensively demonstrated, although the two systems are fundamentally different in that the former is out of equilibrium. We elucidate the origin of the negative viscosity and propose a simple model that reproduces the phenomena observed in this active fluid.

Nonlinear rheological properties of chiral crystal cholesteryl oleyl carbonate (COC) in blue phase III are investigated under different shear deformations; large amplitude oscillatory shear, step shear deformation, and continuous shear flow. Rheology of the liquid crystal is significantly affected by structural rearrangement of defects under shear flow. One of the examples on the defect-mediated rheology is the blue phase rheology. Blue phase is characterized by three dimensional network structure of the disclination lines. It has been numerically studied that the rheological behavior of the blue phase is dominated by destruction and creation of the disclination networks. In this study, we find that the nonlinear viscoelasticity of BPIII is characterized by the fracture of the disclination networks. Depending on the degree of the fracture, the nonlinear viscoelasticity is divided into two regimes; the weak nonlinear regime where the disclination network locally fractures but still show elastic response, and the strong nonlinear regime where the shear deformation breaks up the networks, which results in a loss of the elasticity. Continuous shear deformation reveals that a series of the fracture process delays with shear rate. The shear rate dependence suggests that force balance between the elastic force acting on the disclination lines and the viscous force determines the fracture behavior.

Spatially and temporally controlled topological defects in nematic liquid crystals (NLCs) are promising for its potential in optical applications. Utilization of self-organization is a key to fabricate complex micro- and nano-structures which are often difficult to obtain by conventional lithographic tools. Using photo-polymerization technique, here we show a polymer-stabilized NLC having a micro-pixelated structure of regularly ordered umbilical defects which are induced by an electric field. Due to the formation of polymer network, the self-organized pattern is kept stable without deterioration. Moreover, the polymer network allows to template other LCs whose optical properties can be tuned with external stimuli such as temperature and electric fields.

Self-organized nano-and microstructures of soft materials are attracting considerable attention because most of them are stimuli-responsive due to their soft nature. In this regard, topological defects in liquid crystals (LCs) are promising not only for self-assembling colloids and molecules but also for electro-optical applications such as optical vortex generation. However, there are currently few bottom-up methods for patterning a large number of defects periodically over a large area. It would be highly desirable to develop more effective techniques for high-throughput and low-cost fabrication. Here, a micropixelated LC structure consisting of a square array of topological defects is stabilized by photopolymerization. A polymer network is formed on the structure of a self-organized template of a nematic liquid crystal (NLC), and this in turn imprints other nonpolymerizable NLC molecules, which maintains their responses to electric field and temperature. Photocuring of specific local regions is used to create a designable template for the reproducible selforganization of defects. Moreover, a highly diluted polymer network (approximate to 0.1 wt% monomer) exhibits instant on-off switching of the patterns. Beyond the mere stabilization of patterns, these results demonstrate that the incorporation of self-organized NLC patterns offers some unique and unconventional applications for anisotropic polymer networks.

Topological defects in nematic liquid crystals (NLCs) are attracting attention in recent years for generating optical vortex beams. In most cases, complex defects structures are stabilized by pre-patterned surfaces and spontaneous control with reconfigurability is not so successfully realized. Here, we use NLCs with negative dielectric anisotropy doped with a small quantity of ionic impurity confined between perfluoropolymer surfaces. Without using a template, a large number of topological defects are stabilized by the reorientation of the NLCs using an AC voltage, which is caused by a periodic density modulation of ions at the perfluoropolymer interfaces. Due to the reconfigurable property of the system, the uniform monodomain can be obtained by several methods, for example, an infrared laser and a weak shear flow. Our results offer a new approach for stabilizing multiple topological defects.

Mechanical response to electrical stimulus has been investigated in a chiral smectic A elastomer. During the application of electric field, the two-dimensional strain tensor was precisely measured by tracking fluorescent beads dispersed on the film. It was found that the shear strain is dominantly induced by the electric field and proportional to the applied electric field.

Xanthan gum exhibits viscoelastic and shear-thinning properties. We investigate the Brownian motion of particles dispersed in xanthan gum solutions that are subjected to simple shear flow. The mean...

We have investigated the phase transition behaviors of an antiferroelectric liquid crystal, which was reported to exhibit a re-entrant phase transition (SmC∗-SmCA∗-SmC∗-SmA in the order of increasing temperature) by application of electric fields. By birefringence and dielectric measurements an electric-field-temperature (E-T) phase diagram was obtained. In the E-T phase diagram, it was observed that the SmC A∗ phase disappears under high electric fields and it is isolated. In addition, there is a boundary line between the high- and low-temperature SmC∗ phases.

The basic concepts laid out in Weber’s 1913 essay: ‘Some Categories of Interpretive Sociology’ constitute ‘the four-stage rationalization-scale of social action and order’. The first stage—the germinal similar action of plural individuals (gleichartiges Massenhandeln); the second—the orderless social action among plural individuals (amorphes Gemeinschaftshandeln); the third—the social action among plural individuals oriented one another to the non-enacted order (Einverstandnishandeln); the fourth—the social action among plural individuals oriented one another to the rationally enacted order (Gesellschaftshandeln). This article aims to show that this scale, unique to the ‘Categories’, is not only an outcome of Weber’s critic of Rudorf Stammler, but also is validly applied throughout the whole ‘Old Manuscript’ of the ‘Economy and Society’.

The research development of ferroelectric and antiferroelectric liquid crystals is reviewed, focusing on our findings. First, their structures are briefly explained and the Landau theories are presented such as the two-layer model and the discrete model. Then, a unique phase having a short pitch helical structure, designated as SmCα*, as along with the electric field effect on it, are discussed on the basis of the discrete model. Lastly, results on the nonlinear dielectric spectroscopy of the soft mode which induces the SmCα* phase are presented.

We first review the discrete model, which is now used to investigate the phase transitions in chiral smectic liquid crystals. The model is shown to successfully explain the field-induced phase transitions experimentally observed in MHPOCBC. In addition, we investigated the roles of interlayer interactions such as nonlinear nearest-neighbor and chiral interactions in detail by using a simplified discrete model.

Characterization of spatiotemporal dynamics is of vital importance to soft matter systems far from equilibrium. Using a confocal laser scanning microscopy, we directly reveal three-dimensional motion of surface-modified particles in the electrohydrodynamic convection of a nematic liquid crystal. Particularly, visualizing a caterpillar-like motion of a self-assembled colloidal chain demonstrates the mechanism of the persistent transport enabled by the elastic, electric, and hydrodynamic contributions. We also precisely show how the particles' trajectory is spatially modified by simply changing the surface boundary condition.

The response of shear stress to a weak ac electric field as a probe is measured in a nematic liquid crystal under shear flow and dc electric fields. Two states with different responses are clearly observed when the dc electric field is changed at a constant shear rate: the flow aligning and non-flow aligning states. The director lies in the shear plane in the flow aligning state and out of the plane in the non-flow aligning state. Through application of dc electric field, the non-flow aligning state can be changed to the flow aligning state. In the transition from the flow aligning state to the non-flow aligning state, it is found that the response increases and the relaxation time becomes longer. Here, the experimental results in the flow aligning state are discussed on the basis of the Ericksen-Leslie theory.

Electrical actuation is investigated in two kinds of chiral smectic liquid-crystal elastomers (LCEs) with different domain structures LCE1 and LCE2: The latter is better than the former in orientational order. Tracking fluorescent beads dispersed on the samples enables us to measure the two-dimensional strain tensors in ferroelectric elastomer films. It turns out that the electric-field-induced strain is polarity dependent and the type of molecular orientation responsible for the strain is specified. In LCE1 the shear strain is dominant, whereas in LCE2 it is comparable to the elongation strain, which is explained by the rotation of the principal axes. The essential differences of the two elastomers are observed in the eigenvalues of the strain tensors. The absolute values for LCE1 are larger than those for LCE2. The difference is discussed on the basis of the domain structures.

The annealing effect of the phase transition in PbIn½Nb½O3 (PIN) crystal was investigated by means of the dielectric constant measurement and the polarizing microscopic observation. Using one and the same sample plate of the PIN, it was observed that the antiferroelectric transition gradually changes into the diffuse phase transition as the annealing temperature increases. On the basis of the observation by an optical microscope, the annealing effect of the diffuse phase transition in the relaxor was discussed.

We observed with a confocal scanning laser microscope the interface between a liquid crystalline polymer (LCP) and polydimethylsiloxane (DMS) after they made contact. The initially flat interface became corrugated and the characteristic length of the corrugation increased gradually. The coarsening rate was found to be controlled by the viscosity (the molecular weight) of the DMS; as the viscosity was increased the rate became slower. The present interfacial instability may be related to the diffusion of the low molecular weight DMS into the LCP.

By using a new system that combines a confocal scanning laser microscope and a rheometer, we observed structural changes and measured shear stress simultaneously in immiscible polymer blends, while they were being subjected to shear flow and an electric field. In three different blends various structural changes were observed, which were all related to the electrorheological effect. These blends were composed of liquid crystalline polymers (LCPs) and oils. In one blend we observed a change from a LCP droplet-dispersed structure to an oil-dispersed one, i.e., a phase inversion, while in another blend there was a change from a LCP droplet-dispersed structure to a network structure. After applying shear flow an oil layer was three-dimensionally observed in the third blend, which had an oil-dispersed structure. In addition, it was found that the layer disappeared under no shear and the annihilation process was accelerated by the application of an electric field.

We performed electrooptical measurements in the smectic-Cα* (SmCα*) phase of the antiferroelectric liquid crystal, 4-(1-methyl-heptyloxycarbonyl)phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC), and showed that the frequency dispersion of the second-order electrooptic response strongly depends on the angle between the polarizer and the layer normal while that of the linear response does not. Usually in the SmCα* phase we can observe both the amplitude mode and the ferroelectric mode by second-order electrooptic spectroscopy. In a particular experimental condition, we succeeded in suppressing the ferroelectric mode contribution in the frequency dispersion spectrum and clearly observed only the amplitude mode. The results were discussed and analyzed on the basis of the phenomenological theory.

Domain-wall structures in the vicinity of the morphotropic phase boundary (MPB) in (1-x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PZN–xPT) mixed crystals (x=5% and 8%) were investigated by means of a polarizing microscope. It was found that the apparent jump of the indicatrix rotation as a function of temperature appears in the MPB region (x=8%) without the poling process, indicating the occurrence of a phase transition between the tetragonal and rhombohedral phases, despite the fact that this transition is known to be observed only in a poled sample in the case of dielectric constant measurements. We concluded that the sharp phase transition between the tetragonal and rhombohedral phases in the PZN–PT crystal can be observed in the small region of 50 µm order even without the poling process. It was also found that the principal axis of the indicatrix slightly rotates in the MPB region, implying the appearance of the lower symmetry phase such as a monoclinic structure.

We investigated the composition dependence of the electrorheological properties of immiscible polymer blends which consist of liquid crystalline polymers (LCPs) and polydimethylsiloxane (DMS). We used two different kinds of LCPs, designated as A and B polymers. We observed that for a fixed ratio of an LCP and DMS (LCP:DMS = 2:1) the electrorheological properties change from type I to type II as the fraction of the A polymer is reduced. Microscopic observations indicate that the change in the electrorheological properties is associated with the structural change; in type I, LCP droplets are dispersed in DMS, while in type II, DMS droplets are dispersed and, furthermore, that the structural change is associated with the miscibility between DMS and the LCPs; the A polymer is partially miscible with DMS, while the B polymer is hardly miscible with DMS. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3673–3680, 2002

The disappearance of ferroelectricity in thin films is discussed in the framework of the Landau theory. The way in which ferroelectricity is lost with decreasing film thickness has the properties of a phase transition. The polarization profiles, the average energy density and the average polarization, which depend on the film thickness, are analytically obtained for various boundary conditions.

Brillouin scattering has been performed on the relaxor ferroelectric Pb(Ni1/3Nb2/3)O3 (PNN) from 80 to 450 K across its Curie temperature. A diffuse phase transition from the paraelectric to ferroelectric phase, associated with a broad phonon frequency dip and a damping maximum, is observed around 200 K. A relaxation mode in the form of a broad Rayleigh wing, whose frequency is strongly temperature dependent above 190 K, is observed and analyzed based on a modified superparaelectric model. Dielectric studies of PNN have also been carried out at several measurement frequencies. The relation between the measurement frequency and the dielectric maximum temperature was analyzed on a modified Vogel–Fulcher model.

Angle dependence of the piezoelectric displacement along the driving electric field was calculated near the morphotropic phase boundary in the perovskite-type oxide family on the basis of the Landau-Devonshire type free energy function. It was found that the piezoelectric displacement in the tetragonal phase near the morphotropic phase boundary takes a maximum when the field is applied along the [111] direction, while the piezoelectric displacement in the rhombohedral phase takes a maximum in the direction, which depends on the values of the elastic and electrostrictive constants. In both phases the piezoelectric displacements are strongly enhanced near the morphotropic phase boundary.

Recetvea in final form November 24, 2001) The temperature-concentration dependence of the low frequency modes below 100cm -1 in the solid solution system (1-x) Pb(Zn 1/3 Nb 2/3 )O 3 - xFbTiO 3 (0 ≤ x < 1) was measured by means of the Raman scattering experiment. It was found that the mode softening in the vicinity of the transition point is suppressed with increasing the PZN concentration and no softening of the lowest frequency mode is observed in the pure PZN. The temperature-concentration dependence of the lowest frequency optical mode was discussed.