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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.

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 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 orientational fluctuations in a homogeneously aligned nematic 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. A theory to analyse the results was developed and by using it the ratios of the elastic constant to the viscosity were obtained.

Electro-optical measurements have been performed around the SmA-SmCα*phase transition point in antiferroelectric liquid crystals MHPOBC and MHPOCBC. In both materials the soft mode condensation is clearly seen in addition to the partial softening of the ferroelectric soft mode. The Curie Weiss law is observed. The comparison of the slopes of these modes shows that MHPOBC and MHPOCBC should be close to the critical point. In addition to these soft modes, a low frequency mode was detected. © 2001 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint, a member of the Taylor & Francis Group,.

We have performed precise measurements of the third-order dielectric constant in an antifer-roelectric crystal MHPOCBC. In the vicinity of the SmA- SmCα* phase transition point an anomalous increase of it was observed. We have developed a Landau theory taking into account the pretransitional fluctuations and shown that the fluctuation can contribute to the third-order response. The anomalous behavior near the transition point was discussed on the basis of the theoretical results.

We investigated the response properties of immiscible polymer blend electrorheological fluids to a pulse field. They were composed of liquid crystalline polymers and polydimethylsiloxane, and were classified into two blend types (type I and type II). It was found that the decay of shear stress after removing the field from both of the blends depended greatly on the pulse duration, the applied shear rate, and the temperature. The response properties are discussed on the basis of our model describing the structural change of the fluids.

We have investigated the pattern fluctuations of electrohydrodynamic convection in a homeotropically aligned nematic layer by means of the dynamic image analysis. The time correlation function C k ...

We have investigated the fluctuation in the electro-hydrodynamic convection(EHC) by developing a method for dynamic image analyses. The fluctuation of images is characterized by the two-time correl...

We have measured the linear and the third-order dielectric constants of an antiferroelectric liquid crystal MHPOBC and mixtures of R and S-enantiomers. In the optically pure and nearly pure samples with the SmCα* phase, the third-order dielectric constant discontinuously increases at the transition point from SmA to SmCα*, while the linear dielectric constant is continuous with a small change of the slope in its temperature dependence. These behaviors were well explained by the Landau theory. The optical purity dependence of the Curie constant was also investigated. The Curie constant slightly decreases as the optical purity is reduced, as predicted by the Landau theory.

The relationship between the electrorheological effect and the structure in an immiscible polymer blend was investigated in detail by observing the transient responses to a step field. It was clarified that the increase of the shear stress consists of two processes, the first and the second modes. The former may be ascribed to the elongation of droplets, and the origin of the latter is the formation of cylinders consisting of viscous polymer.

We have found two different types of mechanism of electrorheological (ER) effect observed in polymer blends of side-chain type liquid crystalline polymers and a dimethylsiloxane, and clarified the relationship between the ER effect and the structure. On the basis of their mechanisms we discuss the electrorheological properties of these two blends.

We present a novel mechanism of an electrorheological (ER) effect found in a polymer blend of a liquid crystalline polymer (LCP) with high viscosity and a polydimethylsiloxane (DMS) with low viscosity. In this type of ER fluid thin layers of DMS are formed between the parallel plates of a viscometer and so the blends separated by them can slide on each other, resulting in the decrease of the apparent viscosity. Under an electric field, on the other hand, the area of the layers decreases and thus the ER effect appears.

We studied the electrorheological properties of a type-I immiscible polymer blend, in which droplets of liquid crystalline polymers are dispersed in a polydimethylsiloxane under no electric field. We measured flow curves of the blend at various applied electric fields under various temperatures, and made optical observations of the structure. Two anomalies were found in the flow curve, indicating that there should be three different structures, which are designated as N, A, and B in the order of increasing shear rate. A is much higher than B and N in viscosity. By optical observations it was clarified that A and B coexist in a certain range of shear rate and there is a sharp boundary between them. In A we found a scaling relation in the flow curve and a dimensionless number Mn′, which is the only one parameter characterizing the state of A.

The liquid crystalline behavior of side-chain liquid crystal polymers (LCPs) resembles that of low-molecular-weight liquid crystals, because it is mainly dependent on interactions between mesogenic side groups. The flexibility of the polymer backbone and the length of the spacer are important factors determining the physical properties because the dynamic properties of the mesogenic groups are influenced by nonmesogenic parts of both the polymer backbone and the spacer chain. The orientational order of the mesogenic groups and the thermal stability of the liquid crystalline states increase when the side-chain LCPs have a highly flexible polymer backbone and a long spacer. The influence of these structures on the physical properties of the side-chain LCPs is examined in this chapter. The thermal, mechanical, optical, electric, and electronic properties of side-chain LCPs depend on the orientational order and molecular dynamics properties of the side-chain LCPs. The dielectric properties and electro-optical effects provide important information about the dynamics and the orientational order. These properties are mainly determined by the characters of the mesogenic side groups, and in the side-chain LCPs, the mesogenic side groups are dominantly assembled into strongly coupled units through the influence of the polymer backbone. In this chapter, the structure and properties of the side-chain LCPs are discussed. In particular, their phase transitions, dielectric properties, and ferroelectric response are revealed. Keywords: spacer; phase transition; X-ray; ESR; dielectric property; electrorheology; spontaneous polarization; field-induced effect; ferroelectricity

The antiferroelectric Goldstone mode in a free-standing film was investigated by means of the electro-optic measurement. The divergence of the relaxation time corresponding to the divergence of the helical pitch was observed. In comparison with the result obtained in a homogeneous cell the surface anchoring effect is discussed.

The effect of magnetic field on the growth of the cholesteric finger pattern has been investigated experimentally. It is found that the cholesteric finger grows along the applied magnetic field and the growth velocity of the finger is enhanced by the magnetic field. The preferred direction of the finger growth is discussed by considering the interaction energy between the director and the magnetic field.

The fundamental physical properties of a side-chain type polysiloxane liquid crystalline polymer, which shows a large electrorheological (ER) effect when diluted with poly-dimethylsiloxane (PDMS), were investigated by means of x-ray diffraction and dielectric measurements. From the results of X-ray diffraction it was found that at about 40°C the polymer undergoes a first-order phase transition from the smectic phase to the isotropic phase. A dielectric absorption due to the δ-process was observed, the activation energy was determined to be 81kJ/mol. In addition, a relatively large conductivity was found in this polymer, the apparent activation energy of which is about 93 kJ/mol.

A new model of the electrorheological (ER) effect for immiscible polymer blends is proposed on the basis of microscopic observations. In the absence of an electric field the polymer with high viscosity is dispersed as droplets in the other polymer with low viscosity, while in the presence of an electric field, the droplets stretch and coalesce to form bridges between electrodes, resulting in the increase of the macroscopic viscosity. A few experimental results are given to confirm the validity of this model.

Topological defects in nematic liquid crystals are ubiquitous. The defects are important in understanding the fundamental properties of the systems, as well as in practical applications, such as colloidal self-assembly, optical vortex generation and templates for molecular self-assembly. Usually, spatially and temporally stable defects require geometrical frustration imposed by surfaces; otherwise, the system relaxes because of the high cost of the elastic energy. So far, multiple defects are kept in bulk nematic liquid crystals by top-down lithographic techniques. In this work, we stabilize a large number of umbilical defects by doping with an ionic impurity. This method does not require pre-patterned surfaces. We demonstrate that molecular reorientation controlled by an AC voltage induces periodic density modulation of ions accumulated at an electrically insulating polymer interface, resulting in self-organization of a two-dimensional square array of umbilical defects that is reconfigurable and tunable., Patterning liquid crystals is essential for their applications in photonics, which is commonly achieved by top-down lithographic approaches. Here, Sasaki et al. show a template-free approach that enables fabricating a large number of ordered square microarrays with tunable lattice on millimetre scale.

We have experimentally investigated the viscosity of nematic liquid crystal mixtures of p-methoxybenzylidene-p′-n-butylaniline (MBBA) and p-ethoxybenzylidene-p′-cyanoaniline (EBCA) in the presence of electroconvection under an ac electric field with 60 Hz. Although the viscosity of the mixtures with negative dielectric anisotropy shows a characteristic decrease in the high-voltage regime, that with positive dielectric anisotropy shows a monotonic increase as the applied voltage is increased. The experimental results suggest that the decrease in viscosity observed only for the mixtures with negative dielectric anisotropy is attributed to the negative contribution of electric stress caused by the anisotropic director distribution of the turbulent state.

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 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.

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.

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.

Second harmonic generation (SHG) has been studied in lithium diborate (Li 2 B 4 O 7 ) single crystal from room temperature up to the melting temperature. The magnitudes of the SHG coefficients d 33 and d 31 , at room temperature are, respectively, 3.1 and 0.4 relative to d 11 of quartz. The decrease of the SHG signal in the high temperature range suggests the possibility of the phase transition to a nonpolar phase.

The piezoelectric constants under two types of engineered domain configurations in perovskite-type oxide ferroelectrics were calculated in terms of the Landau-Devonshire-type free-energy function. It was found that the piezoelectric constants under the engineered domain configurations increase on approaching the morphotropic phase boundary, and diverge at the morphotropic phase boundary, if the free-energy function is truncated at the fourth order in the polarization. The physical properties of the engineered domain configurations were discussed.

The temperature-concentration phase diagram in the (1-x) Pb(Zn1/3Nb2/3)O3–x PbTiO3 mixed crystal system was obtained from dielectric measurements, and the temperature dependences of the Raman spectra in the entire concentration range were measured. The lattice vibration and nano-scale clusters in the mixed crystal system were discussed on the basis of observed Raman spectra.

The electrooptical responses of antiferroelectric liquid crystals (AFLCs) under bipolar pulse voltages for the ariving scheme actually used in practice have been investigated. The samples used were 4-(1-trifluoromethylheptyloxycarbonyl)phenyl-4′-octyloxybiphenyl-4-carboxylate (TFMHPOBC) and its homologues. It was found that the V (applied voltage)- T (transmittance) characteristics were affected by the chemical structures such as the type of chiral radical and the length of the alkyl chain. The V-T curves at low temperatures showed an anomalous behavior, i.e., in addition to the usual increase of the transmittance in the low voltage region the transmittance has a maximum and a minimum in the high voltage region.

The holding characteristic of the dark state of antiferroelectric liquid crystal (AFLC) displays have a crucial effect on the contrast ratio. We have studied the dependence of the transmittance in the dark state on the waveform of the applied voltage in multiplex driving for several materials. The samples used were 4-(1-methylheptyloxycarbonyl)phenyl-4′-octyloxybiphenyl-4-carboxylate (MHPOBC) and its homologues. It was found that the holding characteristics of the dark state are affected by the applied waveforms and the chemical structures such as the type of chiral radical and the length of the alkyl chain.

A multiplex-driving technique for an antiferroelectric liquid crystal device has been studied. A new driving scheme is proposed, which overcomes the disadvantage of slow switching from a ferroelectric state to an antiferroelectric state. It is confirmed that the antiferroelectric liquid crystal device can be driven at a high duty ratio of 1/500 by using this scheme.

Field-induced antiferroelectric-ferroelectric phase transition in an antiferroelectric liquid crystal 4-(1-trifluoromethylheptyloxycarbonyl)phenyl-4'-octyloxybiphenyl-4-carboxylate (TFMHPOBC) was studied by means of microscopic observation during the switching process and the measurement of the T-E hysteresis loops. It was clarified that the threshold voltage of the switching from the antiferroelectric state to the ferroelectric state and the transmittance at the threshold voltage depend on temperature, frequency and optical purity. The optical purity is an important factor for improving the contrast of display devices.

We studied phase transitions in an antiferroelectric liquid crystal TFMHPOBC (C8H17O-&benzf;-&benzf;-COO-&benzf;-*CH(CF3)C6H13) by means of dielectric measurements and microscopic observations. Both a Goldstone mode and a soft mode were observed in the SmC* phase, but only a soft mode in the SmCA * phase. From the temperature dependence of the relaxational frequency, it was clarified that the ferroelectric mode tends to be soft even in the antiferroelectric phase transition. The unwinding process of the helical structure in the SmCA * phase was observed with a reflecting microscope. It was also found that all the transitions, i.e., SmA-SmCA *, SmA-SmC* and SmC*-SmCA *, are of the first order. We present the E(electric field)-T(temperature) phase diagram of the optically pure TFMHPOBC and the mixture of R- and S-enantiomers.

The influences of alignment materials on switching properties in antiferroelectric liquid crystals have been studied by using three kinds of polyimide resins. It has turned out that the threshold voltages of the switching between an antiferroelectric state and a ferroelectric state depend on the alignment materials, and that response times are also affected by the alignment materials.

A new antiferroelectric liquid crystal (AFLC), 4-(1-methylheptyloxycarbonyl)phenyl 4'-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC), was synthesized and an unidentified phase (designated as SmCx) was observed between the paraelectric SmA phase and the antiferroelectric SmCA * phase by means of thermal, dielectric and electrooptical measurements. Thermal and dielectric studies suggest that the SmA-SmCx phase transition is of the second order and the SmCx-SmCA * phase transition is of the first order. Two types of electrooptical responses were observed in the SmCx phase: at relatively high temperatures the tristable switching appeared and at low temperatures tetrastables switching was noted. These features are discussed in terms of field-induced transitions.

Smectic layer structure and switching behavior in antiferroelectric liquid crystals TFMHPOBC, TFMHPDBC and MHPOBC were studied. At the phase transition point between SmC* and SmCA *, discontinuity in the leaning angle and the layer spacing was observed. In the SmA phase, diffraction peaks attributable to the focal conic texture and the planar layer structure were observed, implying that the bookshelf structure and the focal conic texture coexist. Using the tristable switching, we designed the fundamental waveforms for multiplex driving and constructed a prototype antiferroelectric liquid crystal display which works at room temperature.

The dielectric dispersion in the ferroelectric and antiferroelectric phases of a smectic liquid crystal, 4-(1-methylheptyl-oxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC), has been measured with several frequencies between 100 Hz and 100 kHz. The soft mode with the Debye-type dispersion was observed in the phase transition from the Sm A phase to the ferroelectric Sm C* phase. In the Sm C* phase, the Goldstone mode was observed at the frequency of about 4.5 kHz. The dielectric dispersion in the Sm CA *, Sm Cα * and Sm Cγ * phases is discussed.

By applying the Landau theory, the appearance of the antiferroelectric phase in smectic liquid crystals and the double hysteresis loop are interpreted. Several types of phase sequences including the antiferroelectric, ferroelectric and/or ferrielectric phase are obtained phenomenologically. The D-E curves in the antiferroelectric phase are classified into three types depending on temperature and the coefficients of the fourth-order terms in the free energy.

The authors propose a model for the arrangement of the phospholipid molecules in a lipid bilayer membrane, based upon both the structure of the fatty acyl chains packed in highly ordered hexagonal arrays below the main transition temperature and the ripple structures in which the ripple lines have a hexagonal symmetry. This assumption results in three kinds of the configurations, whose boundaries make the angle of 120° among them. According to this domain structure, the texture appearing on the freeze-fractured surface in the ripple phase can be explained consistently, and furthermore, the kinetics of the domain boundary motion can be understood satisfactorily.

The space group of the low temperature phase of sodium azide NaN 3 was confirmed to be a monoclinic C 3 2h . The distinct phase front could be seen by polarizing-microscopic observations at the trigonal-monoclinic transition, suggesting that the transition is of the first order. A drastic change in specimen dimension observed by dilatometric measurements supports the first order transition. On the basis of detected anomalies in strain the pressure-temperature phase diagram is produced in the range up to 250°C and 6 kbar.