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In the liquid crystal MHPOBC (4-(1-methylheptyloxycarbonyl)phenyl 4‘-octyloxybiphenyl-4-carboxylate), doxyl spin probe was dissolved and ESR spectra were observed in the antiferroelectric and ferroelectric smectic phases. The molecules of the liquid crystal in the tube- and sandwich-type cells were oriented by the static magnetic field before measurements. An anchor effect of the cell surface on the molecules of the liquid crystal was discussed. Angular variation of the spectra was discussed in connection with alignment of the spin probes in the cells and with the structure of the liquid crystal in the smectic phases.

The nonlinear after-effect functions and susceptibilities for uniaxial ferroelectrics and ferroelectric liquid crystals are derived on the basis of equations of motion. The ferroelectrics and the ferroelectric liquid crystals are quite different in the functional forms of nonlinear after-effect functions and the nonlinear susceptibilities, though they are the same in those of the linear ones. On the basis of the results the validity of so-called Nakada's formula, which has been often used in analyzing experimental data, is also discussed.

Dynamics of interacting +1 and -1 disclinations in the two-dimensionally aligned nematics was investigated experimentally. A position and a sign of individual disclination were measured from the image of polarizing microscope, and then the spatial distribution of disclinations was analyzed by calculating the correlation functions of the number density of disclinations and the distribution functions of the separation of k th-nearest-neighbor disclination pairs. As a result of the interaction among the disclinations, the distribution of disclinations deviates from the random distribution. Each disclination is influenced strongly by other disclinations existing within a distance less than several times of the nearest-neighbor distance. In addition, the correlation functions of the number density of disclinations obtained in the experiment can be well described by the theory for the vortices in the two-dimensional XY system [F. Liu and G. F. Mazenko: Phys Rev. B 46 (1992) 5963].

We have investigated the linear response of shear stress to ac electric fields under shear flow in a nematic liquid crystal. The experimental results were compared with the theoretical results derived from the Ericksen-Leslie theory. Although close agreement was obtained at low shear rates, discrepancies were observed at high shear rates. By introducing a two-mode coupling model the experimental results were well reproduced for the entire range of shear rates, and nonconservative forces were found to play an important role in determining the fluctuation dynamics, which is a characteristic of nonequilibrium steady states.

The apparent shear viscosity of p-methoxybenzylidene-p'-n-butylaniline in the presence of electrohydrodynamic convection (EHC) is investigated experimentally. In the absence of an electric field, directors are almost aligned along the flow direction such that the viscosity is close to the minimum of the Miesowicz viscosities. Since EHC disturbs the flow-aligned director configuration, the viscosity increases as the applied voltage is increased in the low-voltage regime. In the high-voltage regime, however, further increasing the voltage leads to a decrease in viscosity. Microscope observations using a rheometer reveal that the decrease in viscosity occurs in the dynamic scattering mode 2 (DSM2) state, whose spatial director distribution is anisotropic due to the shear flow. By adopting the Ericksen-Leslie theory for the shear flow under the electric field, we find that the viscosity decrease can be attributed to the negative contribution of the electric stress caused by the anisotropic director distribution of the DSM2 state.

査読付原著論文, インパクトファクター(7.37), 被引用回数(0), 責任著者 Toshiyuki Nakagaki, doi/10.1103/PhysRevLett..109.248303

The measured conductivity of KSnOPO 4 (KSP) single crystals in the range from 100 Hz to 1 MHz in our previous work depends on frequency, but this dependence is considered to be due to the influence of the displacement current. It is shown that the analysis of the conductivity data of KSP, containing contributions both from the ionic conduction and the displacement current, can well explain the frequency and temperature dependences of the conductivity.

Mechanism of electric conduction in a hydrous electro-rheological fluid has been investigated. Simultaneously with a rheological measurement, an electric current under a sinusoidal electric field was monitored by using a digitizing oscilloscope, and was separated into a conduction current and a displacement current by means of Fourier analysis. It has been found that the conduction current and the viscosity correlate to each other, and the suspension has a nonlinear conductivity, though the silica particle itself has ohmic conductivity. Microscopic observations were also made and the results indicate that the conduction current passes the cluster of particles spanning between the electrodes. On the basis of the experimental results a simple cluster model for the electric conduction is developed, which can explain the correlation between the conduction current and the viscosity, and the nonlinearity of the current response.

The dispersion formula of the third order susceptibility has been obtained on the basis of a free energy function, and it is compared with the experimental data obtained in a liquid crystal in its SmA phase. The higher order after-effect functions is discussed.

In the electro-hydrodynamic systems of nematic liquid crystals with free and rigid boundaries and a small aspect ratio, the pattern evolution process on applying the stepwise ac voltage was studied. The convective rolls appeared at the both lateral sides of the system, and evolved toward the center. It was found that the pattern is selected through the phase jump. The pattern in the free lateral boundary cell had more flexibility than in the rigid lateral boundary cell. The interactions between the two subsystems separated by free lateral boundary and the selection of the pattern were studied. It was found that the evolution and the selection of the pattern in a subsystem were affected by those in the other subsystem through the free boundary.

We measured the D - E hysteresis loop of TGS (triglycine sulphate), and transformed it to the q - E hysteresis loop by a method proposed in this paper, where q is the volume fraction of reversed domains. The experimental result was compared with a theory based on the Avrami model by the present authors [H. Orihara, S. Hashimoto and Y. Ishibashi: J. Phys. Soc. Jpn. 63 (1994) 1031], in which the volume fraction is expressed as q ( E )=1-exp (- f - d Φ( E )), where f and d are, respectively, the frequency of the applied field and the growth dimension of domains, and Φ is a function of E . We obtained a good agreement between them and confirmed the validity of our theory. The frequency dependences of the coercive field and the area inside the loop were measured and power laws were obtained with respect to them, which are discussed on the basis of the theory.

The D - E hysteresis loop of ferroelectrics is theoretically studied on the basis of the extended Avrami theory. If the sideway velocity depends only on the instant value of the applied field, the volume fraction of the reversed area is expressed as q ( E )=1-exp (- f - d Φ( E )), where f and d are, respectively, the frequency of the applied field and the growth dimension of domains, and Φ is a function of E . This result is obtained irrespective of the waveform of the applied field and the field dependence of the sideway velocity, if the nucleation event is deterministic. For the stochastic nucleation due to thermal fluctuation, on the other hand, the above result is modified as q ( E )=1-exp (- f -( d +1) Φ( E )). The effect of the delay of wall motion is also discussed.

Brownian motion in a simple shear flow has been experimentally investigated by using a different method for observation and analysis. A number of polystyrene spheres dispersed in sheared water were tracked with a confocal scanning laser microscope, and the time dependences of their coordinates were obtained. Since in the usual mean-square displacement in the flow direction the contribution from the Brownian motion is overwhelmed by that due to the convection, we considered an alternative displacement for which the convection effect could be removed. We found that the new mean-square displacement consists of the normal Einstein diffusion term, which is linear in $t$, and an anomalous ${t}^{3}$ term arising from the coupling between the diffusion along the velocity gradient and the convection.

The mechanical response to electrical stimulation was investigated in a chiral smectic elastomer. The two-dimensional strain tensor in an elastomer film was precisely measured by tracking fluorescent beads dispersed on the film. Shear deformation in the film was clearly observed when an electric field was applied perpendicular to the film surface. The temperature dependence of the strain tensor was also investigated, and the origin of the electric-field-induced shear strain in the chiral smectic-$C$ phase was mainly attributed to the Nambu-Goldstone mode.

We have investigated the structural change of an immiscible blend consisting of two polymers with equal viscosity subjected to a step electric field under shear flow. During the process, three-dimensional images were successfully acquired with a confocal scanning laser microscope, and at the same time, the transient shear stress was also measured. From the images, the interface tensor was calculated. In a blend of polymers with equal viscosity, the total shear stress may consist of the viscous, interfacial, and electric stresses. An experiment was performed to separate these stresses, and the results are discussed in terms of the interface tensor.

We have measured the nonlinear dielectric susceptibilities, α3,o' α3 l and α5,0 of a ferroelectric liquid crystal in the paraelectric phase (SmA). The results were analyzed by using the Orihara and Ishibashi theory, which was derived from the time-dependent Ginzburg-Landau (TDGL) equation. The dispersions of the nonlinear susceptibilities and the Cole-Cole plots obtained from the experiment were well reproduced by the theory. The relaxation times obtained from the different nonlinear susceptibilities were almost the same with the one from the linear susceptibility, indicating that there should be only one relaxation time in the system even when the nonlinear phenomena are concerned. As a result we have shown that the TDGL equation is still valid in obtaining the nonlinear susceptibilities as well as the linear one.

The Goldstone modes in antiferroelectric liquid crystals with various optical purities were observed by means of the photon correlation spectroscopy. It was clarified that the helical pitch diverges at a certain temperature in the SmCA* phase and a simple relation with respect to it as a function of temperature and the optical purity was obtained. The bend elastic constant was found to show a discontinuous increase at the transition point from SmCA* to SmC. We investigated the dipole-dipole interaction to explain this increase and the dependence of the bend elastic constant on the temperature and the optical purity.

A discrete model of ferroelectric and antiferroelectric phases, which takes into account the molecular interactions up to the second-nearest neighbors, has been proposed. On the basis of the model the dispersion relation of normal modes and the temperature dependence of the helical pitch for four types of phase sequence are obtained. It is clarified that the experimentally observed phenomena such as the reverse of the helical sense at the SmC * -SmC A * transition point and the divergence of pitch in the SmC A * phase are caused by the chiral interactions between layers.

Photon-correlation spectroscopy was performed to observe relaxation modes in an antiferroelectric liquid crystal (R)-MHPOBC. A phase mode in the SmI A * phase, which is the same as one in the incommensurate phase of solid, was observed for the first time. From the dispersion relations of the Goldstone modes in the SmC γ * and SmC A * phases, the ratios of orientational elastic constants to the viscosity coefficient were obtained as a function of temperature. A linear temperature dependence of the inverse pitch in the SmC A * phase was also found, which was discussed on the basis of the phenomenological theory.

We have derived expressions for the nonlinear dielectric susceptibility of a ferroelectric liquid crystal and a uniaxial ferroelectric crystal on the basis of equations of motion. Our results are different from a formula proposed by Nakada [O. Nakada: J. Phys. Soc. Jpn. 15 (1960) 2280], which was obtained from a tentative assumption. The temperature and frequency dependences of the third-order dielectric constant of a ferroelectric liquid crystal will be presented.

The droplet coalescence process was investigated in immiscible polymer blends when subjected to a step electric field. We present sequential three-dimensional images captured during the process with a confocal scanning laser microscope. Characteristic lengths parallel and perpendicular to the electric field were obtained from the spatial correlation functions of the images. It was found that the droplet growth rate increased with both the electric field and the volume fraction of droplets. A function describing the droplet growth rate was derived from theory using the "hierarchical model" and was found to be in good agreement with the experimental results.

Ferroelectric switching times are theoretically discussed and found to depend upon the sample size. If the switching time is measured using the switching current transient, it becomes shorter with decreasing sample size.

The electro-hydrodynamic instability was investigated in a nematic liquid crystal cell with the free boundary condition on the sides and with a small aspect ratio. In such a free lateral boundary cell, a transition from quasi-periodicity to chaos was observed by measuring the angle-deflective oscillation when the applied voltage was increased. The correlation dimension in the chaotic state was obtained from the time sequence of the transmission intensity.

Dynamics of interactive disclinations in a nematic liquid crystal cell, which can be regarded as the two-dimensional XY-system, has been investigated. We made numerous wedge disclinations of the strength ±1 and observed the annihilation process by means of a polarizing microscope. By analyzing the image, it is found that the number of disclinations N ( t ) decreases as N ( t )∼ t -1 and the dynamical scaling law holds. Furthermore, the correlation function obtained by experiments is discussed by applying the theory of the two-dimensional XY-model.

The Kolmogorov-Avrami-type formulation for both the latent nucleation (inhomogeneous) and the random nucleation (homogeneous) cases is presented for finite systems. In finite systems, there appear three time regimes. For the latent nucleus case the fraction of transformed regions remains as 1- e - N V ( N : density of nuclei, V : system volume) and for the random nucleation case it approaches unity in the time dependence as 1- A e - J V t ( A : constant, J : nucleation rate). The growth rate in finite systems is always smaller than that in infinite systems. We present the numerical results of one-dimensional system as an example.

DC field dependence of the dielectric dispersion in the 2/7 phase of betaine calcium chloride dihydrate was measured in the frequency region between 100 Hz and 10 MHz. It was found that there exists a dielectric dispersion, and both the relaxation frequency and the reciprocal strength are proportional to the DC field strength, therefore their ratio is independent of the DC field strength. We discussed these results on the basis of the phenomenological consideration taking the interaction between domain walls into account.

We have measured the response of shear stress to ac electric fields under steady shear flow in the droplet-dispersed phase of an immiscible polymer blend. A characteristic mode was found under steady shear flow, the relaxation frequency of which increased with increasing the shear rate. In the frequency dispersion, a scaling relation derived from dimensional analysis was confirmed to hold. The origin of the mode was investigated on the basis of the Maffettone-Minale (MM) model, in which the droplet shape is described by a second-rank tensor. The frequency dispersion of the response was also calculated using a modified MM model.

Oscillatory measurements of a columnar structure were performed, which was formed in an immiscible polymer blend subjected to an electric field. The formation process was observed through a confocal scanning laser microscope and the structure for the measurements was confirmed to be well defined. The storage shear modulus at low frequencies increased with increasing the electric field. A linear relation was found between the storage shear modulus and the square of the electric field. The static modulus calculated on the basis of the Maxwell stress exerted on the interface and interfacial tension was in good agreement with the experimental result.

The temperature dependence of phase mode relaxation frequencies in the SmC A * phase (antiferroelectric phase), SmC γ * phase (ferrielecric phase) and SmC * phase (ferroelectric phase), and the dispersion of the phase mode in the SmC γ * phase were measured by photon correlation technique in R-MHPOBC (C 8 H 17 – –COO– –COO * CH(CH 3 )C 6 H 13 ). The relaxation frequencies of the phase modes in SmC A * and SmC * are almost the same and are much higher than that in the SmC γ * phase. The relaxation frequency gradually decreases with decreasing temperature in the SmC A * phase. In the SmC γ * phase, the phase mode shows a parabolic dispersion.

Dynamics of interacting disclinations is investigated by utilizing bubble domains. A pair of wedge disclinations with strength of +1 and -1 emerge from bubble domains when a suitable electric field is applied, and the density of disclinations can be controlled by adjusting the field. To investigate the interaction between the disclinations, the time evolution is analyzed on the basis of the equation of motion for the disclinations.

We observed ferroelastic domain of LaNbO 4 crystals by micro-Raman spectroscopy utilizing a specific band (107 cm -1 A g mode) with the polarization condition. We found the variation of the Raman intensity corresponding to the ferroelastic domain structure, which is caused by the rotation of crystallographic axes in each domain. The results were in accordance with the optical microscope image with a good reproducibility, proving the feasibility of micro-Raman spectroscopy in the study of domain structures.

The temporal evolutions of the assembly of disclination lines, as well as of a single line, are studied from the fractal viewpoint. It has turned out that the fractal dimension of the assembly is almost 2, while that of the single line is 1.65. We confirmed the validity of the relation µ=( D - D T )ν, where µ and ν are the exponents with respect to the disclination length and the characteristic length, respectively, and D and D T are the fractal and topological dimensions, respectively.

GaPO4 single crystals of the low-temperature form were hydrothermally grown in 4M H3PO4 solution at 180 ° C. Single crystals 5.0×5.2×3.7mm3 in size could be grown in a silica glass vessel of 10 mm inner diameter. The dielectric properties of grown crystals were measured with the electric field parallel (E ∥c) and perpendicular (E ⊥c) to thec-axis. The values of dielectric constant (ie2800-01) ofE ∥c andE ⊥c are about 10.3 and 7.8, respectively, at frequencies from 10 kHz to 1 MHz, and these are nearly independent of frequency at room temperature. However, these values increase with temperature in the temperature range about 310 to 500 K and in the frequency region below 1 MHz. Dielectric loss (ie2800-02) increases with increasing temperature at around 300 K (E ∥c) and 310 K (E ⊥c). From the log σ (conductivity) against 1/T plot in the intrinsic region at higher temperatures, the values of activation energy (E) for conduction are calculated to be about 0.17 and 0.33eV, forE ∥c andE ⊥c, respectively.

The Raman spectra of α-GaPO 4 single crystals have been investigated. In the polarization measurements at room temperature under atmospheric pressure we observed seven new Raman lines, not observed so far. In addition, the measurements of the temperature and pressure dependences of Raman spectra show the results which are well in accordance with those obtained for the single crystals of the same structure such as quarts and AlPO 4 .

The disclination pattern, emerging in the ordering process after the non-orthogonally twisted nematics is quenched, showed quite different features from that of orthogonally twisted nematics. Dynamical scaling law found in the orthogonally twisted nematics does not hold. By introducing, however, the characteristic time and characteristic length from the equation of motion of single disclination line, we have found a scaling property in these systems.

We found a stripe formation in an emulsion of a liquid crystalline polymer (LCP) and a machine oil (OIL) in electric and shear fields. Through the simultaneous measurement with a confocal scanning laser microscope and a rheometer, it was clearly shown that the formation of stripes, which are periodically arrayed, leads to the increase of the shear stress. The droplets, which are one component of the emulsion, start to be connected at low electric fields and then change into the stripes with the increase of electric field. Finally, a three-dimensional network is formed at high electric fields. The period and fluctuation of the stripe structure were also investigated in detail.

A distribution of Cu ions in polyelectrolyte film (Nafion) is directly observed with a small-angle X-ray scattering (SAXS) method utilizing an X-ray anomalous dispersion effect. A partial structure factor of the Cu ions, GAA(q), can be derived from the SAXS profiles obtained by scanning the incident X-ray energy around the Cu K absorption edge. GAA(q) has two peaks, indicating that the Cu ions hierarchically distribute in Nafion film. In addition, a standard SAXS also shows that Nafion film has a hierarchical structure. These results mean that the Cu ions locate in the domain where the hydrophilic bases aggregate.

The orientational fluctuations in a smectic liquid crystal were successfully observed with a high-speed video camera. From the series of images obtained, first the spatial Fourier transformation of each image was computed and then the time correlation function at each wave number was calculated. It was found that the time correlation function shows an exponential decay and the inverse of the relaxation time is proportional to the square of the wave number. The ratio of the elastic constant to the viscosity was also obtained in this experiment.

Dynamics of phase solitons in the polar commensurate phase is analysed in the framework of the phenomenological model usually used to describe the commensurate-incommensurate phase transition of the first kind, assuming the continuous order parameter and the constant amplitude approximation. Comparison with domain walls in the usual ferroelectric phase is provided. While the mobility of a usual ferroelectric domain wall diverges at the continuous phase transition to the disordered state, soliton mobility remains finite at the commensurate-incommensurate phase transition.

Dielectric measurement was carried out on an immiscible blend of a side-chain type polysiloxane liquid crystalline polymer (LCP) and a poly-dimethylsiloxane (PDMS), which has a large electrorheological (ER) effect, in the frequency range from 100 Hz to 10 MHz and over the temperature range from 25°C to 105°C. Two relaxation processes were observed; one is due to the mesogenic motion, i.e., the δ-process of LCP and the other to the Maxwell-Wagner effect originating in the conductivity of LCP dispersed in PDMS. The results were analyzed in terms of the Clausius-Mossotti (CM) approximation and the local field exerted on droplets of LCP was discussed.

The temperature dependence of the microwave relaxation in the vicinity of the main polar commensurate phases ( q s / c * =2/7, 4/15) of betaine calcium chloride dihydrate (BCCD) is ascribed to activated overdamped modes on the phason branch. Quantitative results are obtained.

We present a precise electric-field-temperature phase diagram of an antiferroelectric liquid crystal with a short pitch Sm-Calpha* phase. This was obtained by using a photoelastic modulator. A unique field-induced phase was found inside the Sm-Calpha* phase, which displayed low birefringence. Two tricritical points related to the phase were also observed. In addition, numerical calculations were made based on the discrete phenomenological model. The numerical results reproduced the experimental ones and it was clarified that the phase has a three-layer structure without spatial modulation.

By using a new system that combines a confocal scanning laser microscope (CSLM) and a rheometer, we observed the structural change and measured the shear stress simultaneously in an immiscible polymer blend. The blend used is composed of a liquid crystalline plolymer (LCP) and a petroline mineral oil (PMO). When subjected to an external electric field, we observed a change from an LCP‐droplet‐dispersed structure to a network structure, corresponding to an increase of the shear stress.

We performed nonlinear dielectric spectroscopy to study the dynamic properties near the smectic-A-smectic-C(*)(alpha) phase transition point of an antiferroelectric liquid crystal 4-(1-methyl-heptyloxycar- bonyl)phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC). A Landau-type theory was developed in order to analyze the experimentally obtained frequency dispersions. From the experimental and theoretical results we successfully obtained the temperature dependence of the relaxation frequency of the soft mode in both the smectic-A and smectic-C(*)(alpha) phases, which gave direct evidence that the transition is brought about by soft mode condensation. Significant features of this transition are also discussed.

We have theoretically and experimentally studied the nonlinear dielectric response under large orientational fluctuations near the Sm-A-Sm-C(*)(alpha) phase transition point in a chiral smectic liquid crystal. The third-order nonlinear dielectric response due to the fluctuations was observed in the vicinity of the transition point. By using it, we have successfully observed the soft-mode condensation inducing the Sm-A-Sm-C(*)(alpha) phase transition.

We performed nonlinear dielectric spectroscopy to study the dynamic properties near the smectic-A-smectic-C(*)(alpha) phase transition point of an antiferroelectric liquid crystal 4-(1-methyl-heptyloxycar- bonyl)phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC). A Landau-type theory was developed in order to analyze the experimentally obtained frequency dispersions. From the experimental and theoretical results we successfully obtained the temperature dependence of the relaxation frequency of the soft mode in both the smectic-A and smectic-C(*)(alpha) phases, which gave direct evidence that the transition is brought about by soft mode condensation. Significant features of this transition are also discussed.

We have experimentally and theoretically investigated the electric-field effect on the smectic-A--smectic-${C}_{\ensuremath{\alpha}}^{*}$ phase transition of an antiferroelectric liquid crystal4-(1-methyl-heptyloxycarbonyl)phenyl ${4}^{\ensuremath{'}}$-octylcarbonyloxybiphenil-4-carboxylate. From the microscopic observations under electric fields and the measurements of the D-E hysteresis loop and apparent tilt angle, the E (electric field)-T (temperature) phase diagram was established, in which a tricritical point was found. From the dielectric measurements under dc electric fields, a soft mode inducing the transition was observed. Furthermore, we have developed a phenomenological theory under dc fields to analyze the experimental results. The origin of the soft mode observed under fields was clarified and the temperature dependence of the relaxation frequency was obtained by the analyses.