The flexible control of nanopatterns by a bottom-up process at the nanometer scale is essential for nanofabrication with a finer pitch. We have previously reported that for the fabrication of linear nanopatterns with sub-5 nm periodicity on Si substrates the outermost surfaces of assembled micelles facing the substrates can be replicated with soluble silicate species generated from the Si substrates under basic conditions. In this study, concentrically arranged nanogrooves with a sub-5 nm periodicity were prepared on Si substrates by replicating the outermost surfaces of bent micelles guided by silica particles. The Si substrates, where silica particles and surfactants films were deposited, were exposed to an NH3-water vapor mixture. During the vapor treatment, cylindrical micelles became arranged in concentric patterns centered on the silica particles, and their outermost surfaces facing the substrates were replicated by soluble silicate species on the Si substrates. The thinness of the surfactant film on the substrate is crucial for the formation of concentric silica nanogrooves because the out-of-plane orientations of the micelles are suppressed at the interface. Surprisingly, the domains of the concentric silica nanogrooves spread to much larger areas than the maximum cross-sectional areas of the particles, and the size of the domains increased linearly with the radii of the particles. The extension of concentric nanogrooves is discussed on the basis of the orientational elastic energies of the micelles around one silica particle. This study of the formation of bent nanogrooves guided by the outlines of readily deposited nanoscale objects provides a new nanostructure-guiding process.

We investigated the novel photo-induced dynamics of azobenzene-doped cholesteric (Ch) droplets coexisting with the isotropic (Iso) phase. When the hemispherical Ch droplets initially stuck to glass substrates were irradiated by UV-light, they were parted from the substrates due to the surface disordering caused by the photo-isomerization of azobenzene. Then, the spherical droplets floating in the Iso phase exhibited an unexpected motion - a continuous and unidirectional rotation along the light propagation direction. The rotational direction was reversed by the inversion of either the sample's chirality or the UV irradiation direction, and the rotational velocity increased with both the UV-light intensity and the concentration of the doped azobenzene, the dependences of which were described by linear and relaxation functions, respectively. We proposed a possible scenario based on Leslie's theory combining mass fluxes and torques, which well explained the photo-driven rotation of the Ch droplets.

When a cholesteric liquid crystal (LC) is submitted to a thermal gradient, it exhibits continuous director rotation. The phenomenon is called the Lehmann effect and is understood as a thermomechanical coupling in chiral LCs without mirror symmetry. Since the Lehmann effect is considered to possess time-reversal symmetry, one can expect the inverse process, i.e., rotating chiral LCs to pump heat along the rotational axis. We report the first observation of heat transport driven by rotating cholesteric droplets. This result suggests a new function of the cholesterics as a micro heat pump.

In an isotropic-cholesteric coexistence system, a single-helix structure is formed in the cholesteric droplets, and when a temperature gradient is applied, unidirectional rotations are induced in these droplets. However, in a previous work, we showed that a double twisted structure was also formed in the droplets by changing droplet size or chirality. In this paper, we find that unidirectional rotations are also induced by applying a temperature gradient to droplets with a double twisted structure. Here, however, the rotational behavior is strongly dependent on the relationship between the direction of the helical axis and the temperature gradient. Unidirectional rotation is induced when one of the helical axes is parallel to the gradient, whereas no rotation is found when all of the axes are perpendicular to the temperature gradient. These results suggest that the macroscopic helix plays a significant role in the heat-driven rotational dynamics of cholesteric droplets.

We found for the first time the stabilization of a double twisted structure in cholesteric liquid crystals confined to small spherical droplets under weak anchoring conditions. The direct observation of the droplets using a polarized microscope revealed the physical properties of the structure. The experimental results showed that the stability of the double twisted structure is determined by the relationship between the helical pitch length and the droplet size. We theoretically analyzed the structural stability by the calculation of the Frank elastic free energy including the surface elastic term, and succeeded in explaining the experimental results. In this paper, we concluded that the stability of the double twisted structure is determined by the competition between the surface and the bulk elasticity.

We revealed the detailed structures of induced smectic liquid crystal (LC) phases composed of a binary mixture of charge-transfer (CT) LC substances. Although neither of the constituents had highly ordered smectic phases, the mixture exhibited smectic-E (SmE) or smectic-B (SmB) phases when mixed at ratios of 1:1 and 2:3, respectively. The results of polarized optical microscopy, differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy indicated that the induced smectic phases were stabilized by an exquisite balance between the CT interactions, dipolar interactions, and excluded volume effects. We proposed a possible model for the molecular arrangements in the SmE and SmB phases, which consistently explained the experimental results including the stoichiometric ratios.

By means of MD simulation, we investigated the cross correlation between c-director rotation and gas permeation through SmC* monolayers with applying a rotational electric field. Our simulation results agree with Onsager relation, which predicts that both the c-director rotation and the gas permeation should linearly depend on the rotational E-field and pressure gradient of the gas.

Binary mixtures composed of polar and non-polar LC molecules often form highly-ordered smectic phases. We recently found that when several percent of dialkyl-terminated azobenzene is added to 8CB, the mixture considerably loses the fluidity without showing any phase transitions. To understand the origin of this phenomenon, we tried to examine the molecular diffusional in the mixture by means of gas permeation experiment.

Free-standing films composed of chiral liquid crystals are known to exhibit the unidirectional director rotation under transmembrane mass flow. The dynamics is well described by Leslie's phenomenological equation, which predicts the inverse process of mass transports driven by the director rotation. In this report, we investigated this inverse effect. Applying a rotating E-field to the film that should drive the unidirectional rotation of the c-director, we simultaneously measured the transported gas through the film.

Recently, in the system where the droplets formed by the cholesteric liquid crystal are dispersed in the isotropic medium, we found double twisted structure is stabilized. As the chirality of the system or the size of the droplets increases, the structure transits from the double twisted into the single helix structure. Moreover, calculating the elastic free energy in the system, we succeeded in explaining the structural transition described above theoretically.

Cholesteric LC droplets dispersed in isotropic phase are known to exhibit a unidirectional barycentric rotation under a temperature gradient. Theoretically, Onsager relation predicts such interesting inverse process that the rotation of cholesteric droplets should transport a heat along the rotational axis. We tried to cause the heat current by mechanically rotating the cholesteric droplets in the isotropic phase. Although a convincing result has not been obtained, we noticed some difference between the cholesteric droplets and nematic ones.

Making isotropic droplets in the cholesteric (Ch) liquid crystal, we found spiral textures appear on the interface between the Ch liquid crystal and the droplets. Moreover, applying temperature gradient to this system, we found the texture rotates. To clarify the origin of this heat-driven rotation, we analyzed the flow field in the system. As a result, it was found convection is induced in the droplet when temperature gradient is applied; thus, we concluded this convection is the physical origin of the heat-driven rotation.

We performed structural analysis of induced smectic phases, which are composed of polar and non-polar liquid-crystalline molecules. Unlike the conventional understanding that induced smectic phases originate from the formation of charge-transfer (CT) complexes, we revealed that when the CT interaction strength is not so strong, the binary system spontaneously selects the specific integer composition ratio other than 1:1. Our results suggest that the structural formation of induced smectic phases exhibits remarkable similarities to that of metal alloys; that is, the structural stabilization is realized by not only the CT interaction, but also the contributions of molecular-packing effects.

We observed diffraction patterns of smectic E (SmE) phase by using our home-made electron microscope. The advantage of our system is the low-electron beam; this significantly reduces the radiation damage to specimen, and enabled us to observe SmE films without any cryogenic technique. We found in particular that diffraction patterns of SmE phase as an induced smectic phase exhibit unidirectional rotations under electron beams. Since such rotations were not observed in the case of usual SmE phase, we revealed that induced SmE phase possesses well-regulated molecular aliments in the in-plane herringbone lattice, which realizes the spontaneous chiral symmetry breaking.

When a chiral liquid crystal is given a transport current, a unidirectional molecular motion is known to take place, which is called the Lehmann effect. In this paper, we study the mysterious heat-current-driven Lehmann effect using two types of hemispherical cholesteric droplets using polarizing, reflecting, confocal and fluorescent microscopies. Both the droplets, coexisting with the isotropic phase and contacting on a glass substrate, are characterized by the concavo-convex modulated surface and the inside orientational helix. Further, the only difference between them is the helical axis direction; i.e., one is perpendicular and the other is parallel to the substrate. Under the temperature gradient perpendicular to the substrate, the droplet whose helical axis is parallel to the heat current exhibited pure director rotation, while that with the axis perpendicular to the current rotated independently as a rigid body. In the two droplets, the rotational conversion efficiency from the temperature gradient into the angular velocity showed very different dependences on the chirality strength and on the droplets' size, suggesting that the rotations of the two droplets may be driven by independent torques with different origins. This is the first observation that the cholesteric droplets under the temperature gradient exhibit the two rotational modes, the pure director rotation and the molecular barycentric motion, which can be switched to each other by changing the heat current direction parallel and perpendicular to the helical axis.

<p>We study the nematic-isotropic interface under an electric field by confocal microscopy. In the N-I coexisting temperature region, the interface is initially flat and is deformed into a periodically modulated shape by a weak AC field. The amplitude and the wavenumber of the modulation monotonically increased with the electric field.</p>

<p>The gas permeability through free-standing LC films is known to depend on the molecular structures and the LC phases. In this report, we examine the dependence of the gas permeability on the dynamical director field, which was inspired by Lehmann effect driven by transmembrane gas transport. We study how the gas permeability is affected by the director field and motion.</p>

<p>In the isotropic-cholesteric (Ch) coexistence phase of a cyano-biphenyl LC with a chiral dopant, we found four types of Ch droplets associated with the crossed, striped, rugb y and concentric-circle (CC) textures under polarizing optical microscopy (POM). When a temperature gradient was applied to the sandwiched cell perpendicular to the glass substrates, the droplets except for the one with the crossed texture showed the cons tant unidirectional rotation. We analyzed the rotational behavior in comparison with the helical structure inside the droplets.</p>

<p>In the coexisitence region of cholesteric and isotropic phases, we observe the hemispherical cholesteric droplets accompanied by the helix inside confined on a glass substrate. Under the electric field parallel to the substrate, the droplets rotate to orient the helical axis perpendicular to the field and at the same time, interact each other. The force between the droplets shows the clear dependence on both the relative direction and the distance between the droplets.</p>

<p>Recently, in the system where the droplets formed by the cholesteric liquid crystal are dispersed in the isotropic medium, it has been reported the textures on the droplets rotate when temperature gradi ent is applied to the system. In this study, to clarify the mechanism of the rotational motion, we analyzed the structure of the droplets and the dynamics of the motion using polarized microscopy and flow-field measurements with photo-bleaching method.</p>

<p>We found an extra-ordinary disruption dynamics of smectic bubbles composed of the binary system of polar and non-polar LC molecules. Unlike the typical liquid-like bursting dynamics seen in usual SmA phase, we observed during the disruption polymer-like, network-formations and dramatically increase in the timescale. Although it has been known that such mixtures exhibit higher ordered induced smectic phase, such dynamics were found even in the case of SmA phase. In this report, we discuss the dependence of the characteristics of dynamical properties on temperature, concentration, and film thickness, and propose the physical mechanism in the light of the 'dynamic asymmetry'.</p>

<p>When an external field such as electric and magnetic fields is applied to a liquid-liquid interface, we often encounter the deformation of the interface. In the case that one of the liquids is liquid crystal, the deformation should be associated with the director modulation. Here, we study the modulated structure of the surface of a liquid crystal sample without any external field. Under the strong anchoring conditions, the competition between the interfacial tension and the interior orientational elasticity should determine the periodic modulation of the interface.</p>

We have carried out molecular dynamics (MD) simulations for monolayers of smectic A and C liquid crystal (LC) phases in order to investigate the in-plane molecular diffusion from the microscopic point of view. In contrast to similar complex two-dimensional systems (e.g., biomembranes) whose molecular diffusion is anomalous, in-plane mean square displacements (MSDs) for both phases increase linearly with passing time similar to typical fluids on the nanosecond time scale. By following the relation between the diffusion and the viscosity in the fluids, we estimated the viscosity coefficients for both LC monolayers, and the obtained values indicate that the smectic A monolayer has a higher viscosity than the smectic C one. Moreover, we investigate the in-plane self-diffusion anisotropy D-parallel to/D-perpendicular to for smectic C and found that the diffusion parallel to the molecular tilt is 1.5 times larger than that in the perpendicular direction. This anisotropic diffusion property in the smectic C monolayer has not been clearly confirmed thus far.

The cholesteric droplets with stripe textures dispersed in the coexisting isotropic medium are known to rotate their textures under a temperature gradient. In spite of the clear observation, it is not known whether the rotation of the stripes should correspond to the director rotation or the barycentric rotation of the droplets. To clarify the rotational mechanism, we investigated the detailed structure of the cholesteric streaky droplets by using polarized and confocal fluorescence microscopy and analyzed the relation between the structure and the rotational speed of the droplets.

The diffusion of small gas molecules in smectic LC films is examined by Molecular Dynamic (MD) Simulation. When the solute molecules are smaller than the solvent constituents, the diffusion is known to deviate from Stokes-Einstein's law, which cannot be described by any general equations. We carried the MD simulation of the gaseous motion in smectic membranes and comparedto some experimental results.

Hemispherical smectic bubbles exhibit nonlinear deformation under a DC field. When a bubble on a flat substrate is given the higher DC field than a threshold, it expands to touch the upper electrode and return back, the process of which is repeated with a constant period. By measuring the electric current through the bubble, we confirmed that the bubbles' nonlinear oscillation should be ascribed to the accumulation and release of the charges on the bubble surface. The oscillation period can be controlled in a wide range by changing the applied voltage and the bubbles' resistance.

We found that the simply intermixing of two monocomponent LC materials induced the unusual phase ordering. In the binary mixture, the transition temperature between the isotropic and LC phases increased significantly, and the higher-ordered phases of SmB appeared at the lower temperature, which could never be seen in either of the original materials. The result of POM observation, DSC and X-ray diffraction measurements suggests that the "anomalous ordering" could be ascribed to a certain kind of micro-phase segregation.

We studied the unidirectional rotation of cholesteric droplets driven by thermal flow. The polarizing microscopy observation showed that the droplets under temperature gradient took two different types of dynamics: When the cholesteric helical axis is parallel to the thermal flow, the transmitted light through the droplets temporally changes its intensity with a certain period, the speed of which increases with the chirality. In contrast, the droplets with the helix axis perpendicular to the heat current showed much slower dynamics, the speed of which decreases with the chirality strength. We suggest that the two dynamics of the cholesteric droplets may correspond to the unidirectional rotation of the director and that of the droplets themselves.

Biaxial nematic liquid crystals have attracted much attention from both fundamental and application points of view, because the fast response based on the rotation of the minor director is expected. So far, different molecular designs have been proposed for the emergence of the biaxial nematic phase. Among that, we have been interested in applying "preorganization" concept on generating the biaxiality. Dimeric liquid crystal compounds have been prepared in line with this concept in which two mesogenic parts are linked by the biphenyl connecting group. The pre-organized dimmer shows an anomalous textural change, for vertically-aligned and free-standing film samples, at the smectic C (SmC)-nematic (N) phase transition, in which the Schlieren texture of the SmC changes into the other Schlieren texture of the N phase. There are two possible explanations for this textural change, i.e., the occurrence of the director change at the SmC-N phase transition or the emergence of biaxiality in the N phase. The electric-field-induced birefringence has also been measured in detail for investigating the biaxial nature of the sample.

Gas permeation through smectic C* free-standing films causes a unidirectional director rotation, occasionally accompanied by a unidirectional vortex-like hydrodynamic flow. In this study, by placing ZrO2 micro-particles on the film subjected to methanol vapor transport, we observed the particle motions and measured a drag force acting on them. The particles underwent a unidirectional quasi-circular motion with the velocity linear to the methanol transfer rate with the magnitude of the drag force being on the order of several pN that increased approximately linearly with the velocity of the flow. A simple analysis shows that the conversion efficiency from the transmembrane methanol current to the drag force on the particles is similar to 1.4 x 10(-10) N.s.m(2)/mol in our system. The present hydrodynamic experiment is complementally to the previous observations of linear director rotation in the Lehmann effect, which well supports Leslie's phenomenological theory. (C) 2011 The Japan Society of Applied Physics

Free-standing films composed of several layers of chiral smectic liquid crystals (SmC*) exhibited unidirectional director precession under various vapor transfers across the films. When the transferred vapors were general organic solvents, the precession speed linearly depended on the momentum of the transmembrane vapors, where the proportional constant was independent of the kind of vapor. In contrast, the same SmC* films under water transfer exhibited precession in the opposite direction. As a possible reason for the rotational inversion, we suggest the competition of two origins for the torques, one of which is microscopic and the other macroscopic. Next, we tried to move an external object by making use of the liquid crystal (LC) motion. When a solid or a liquid particle was set on a film under vapor transfer, the particle was rotated in the same direction as the LC molecules. Using home-made laser tweezers, we measured the force transmitted from the film to the particle, which we found to be several pN.

Orientational correlations in Langmuir monolayers of nematic and smectic-C liquid crystal (LC) phases are investigated by molecular dynamics simulation. In both phases, the orientational correlation functions decay algebraically yet with the different exponents of 1.9 and 0.2 for the nematic and the smectic-C monolayers, respectively. The power law decay, i.e., the absence of long-range orientational order, means the both monolayers should be the ideal 2D system with a continuous symmetry, whereas the large difference in the exponents of power law gives rise to the crucial difference in their optical properties; the nematic monolayer is optically isotropic while the smectic-C monolayer exhibits an anisotropy on the length scale of visible light. Since the exponent is inversely proportional to the molecular exchange energy, the averaged molecular interaction in the nematic monolayer should be an order of magnitude smaller than that in the smectic-C monolayer, which is ascribed to the low molecular density and the weak molecular dipole due to the water molecule. The relation between the molecular interaction and the orientational correlation calculated for the 2D LC system offers much information not only about the 2D LCs but also on the bulk system. (C) 2011 American Institute of Physics. [doi:10.1063/1.3536519]

Hemispherical bubbles composed of smectic liquid crystals show an unusual deformation under DC electric field. When the lower voltage than a threshold is applied to the bubble on a substrate, it is elongated in the direction of the electric field and forms a semi-elliptical shape in the equilibrium. With the higher voltage than the threshold, the bubble becomes unstable and sometimes exhibits a periodic oscillation with repeating the elongation and shrinkage. Based on a simple equation of force balance, we analyzed both the static and dynamic deformations under DC field and successfully reproduced the observed behaviour. By the detailed analysis, we also determined the surface tension and the electric conductivity of the smectic bubbles.

Pre-organization effects are investigated for the laterally-connected liquid crystals possessing a biphenyl connecting group. The homeotropic texture of the N phase of a free-standing film sample was found to change into the other "Schlieren" texture on cooling even in the N phase, which then changes into the "Schlieren" texture of the SmC phase on further cooling. The possibility of the emergence of biaxiality in the N phase is discussed.

Molecular dynamics simulations were performed for an axial-chiral liquid crystalline (LC) monolayer under trans-monolayer gas flow. The rotational dynamics of the monolayer chiral LC molecule along its long-molecular axis were analyzed at the molecular level. We found a precise correspondence between the flow-driven molecular rotation direction and molecular chirality as well as between the rotation direction and the trans-monolayer flow direction. The rotational direction exactly corresponded to what was expected in the proposed chiral molecular propeller model (Tabe, Y.; Yokoyama, H. Nat. Mater. 2003, 2, 806). Among the four trans-monolayer gas species we investigated, we found argon to be the most efficient at driving the chiral molecular propeller and helium the least efficient.

Gas permeation through liquid crystal (LC) films was examined using hemispherical smectic bubbles. A smectic bubble, when the inside and the outside are filled with different gases, should expand or shrink toward the quasi-equilibrium state, where the influx and efflux caused by osmotic pressure are balanced. Deriving a simple formula that directly converts the quasi-equilibrated bubble radius to the gas permeation, we determined the absolute permeability coefficients of 8 simple gases through the smectic bubble. The permeability was distributed in such a wide range that carbon-dioxide had more than 20 times larger value than nitrogen, the dependence of which on the gas species was mostly dominated by their solubility into the LCs. Dividing the measured permeability by the calculated solubility, we obtained the diffusion constants as well, yet whose magnitude and the dependence on the solute size could not be explained by either conventional continuum theories or microscopic diffusion models. In order to describe the diffusion of small solutes in the liquid solvent composed of large molecules, a new theoretical framework may be necessary.

We investigated photochemical transformation of asymmetric topological defects formed around water droplets dispersed in the azobenzene-containing liquid crystals. It was found that initial structures and the photo-induced phenomena of the defects were clearly affected by chemical structures of the azobenzene compounds. In quite strong homeotropic anchoring obtained by using the azobenzene compound with a long alky chain, the hedgehog was formed around the droplets at the initial state. When the anchoring strength was decreased by changing the carbon number of the alkyl chain, a novel asymmetric defect which will be an intermediate structure between the hedgehog and the Saturn ring was observed. The ionic groups had an influence on the photochemical transformation of the defects. The azobenzene compound with a smaller ionic group induced only a change in the anchoring strength, and a disappearance of the hedgehog was observed on the irradiation with ultra-violet light. In the case of the azobenzene compound with a larger ionic group, photochemical switching of the anchoring and the transformation into the boojums was achieved. The photo-induced phenomena could be qualitative explained by an effectiveness of the cis-trans photoisomerization depending on molecular areas of the azobenzene compounds determined by the ionic groups. (C) 2008 Elsevier B.V. All rights reserved.

Photonic control of defect structures and colloidal chains has been performed in azobenzene-containing liquid crystals dispersed with glycerol or water droplets. When we dispersed the colloidal droplets into the host liquid crystals, we could observe, at an initial state, Saturn ring and hedgehog around the glycerol and water droplets, respectively, indicating that normal alignment of liquid crystal molecules was induced on the droplets by the adsorption of the azobenzene molecules onto the droplets. In the case of the glycerol droplets, we achieved photochemical manipulation of the defect structures between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, an inter-droplet distance of the self-organized colloidal chain could be controlled by changes of the defect size on the photoirradiation. Photoinduced structural changes in the topological defects can be explained by the modulation of surface anchoring of the droplets by means of the cis-trans photoisomerization of the adsorbed azobenzene molecules.

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 polarization (P-s) directions. It suggests that in our simulations, P-s and its direction were determineded as the "biased distribution" within much shorter time scale than that for the "hindered rotation".

Hydrophobic compounds of smectic liquid crystals are spontaneously spread on a liquid surface to form softly-condensed monomolecular films. The constituent molecules are coherently tilted from the surface normal when they form smectic-C phase in the bulk state, while the molecules are aligned perpendicular to the surface when they form smectic-A or -B phase in the bulk. The result proves that the tilting property in the smectic liquid crystals should be determined only by the intralayer molecular interaction. The molecular dynamics simulations can reproduce the experimental result satisfactorily and also suggest that the molecular dipole moment should play an essential role to cause the coherent molecular tilt in smectic liquid crystals.

A phenomenon is presented, which changes the shape of gas bubbles in liquid crystals and also creates long gas tubes. The system consists of air bubbles which are injected into a nematic liquid crystal host. The shape of these air bubbles changes from spherical to ellipsoidal by initiating freezing of the sample. Furthermore, long gas tubes are formed from the air which was formerly dissolved in the liquid crystal. The gas tubes are created by the progression of the crystalline-liquid interface. Their length can reach up to 40 times their diameter. The diameter of the tubes depends on the pressure applied to the system, as well as on the interface velocity.

We investigated photoresponsive behavior of azobenzene-containing liquid crystals dispersed with glycerol or water droplets. At an initial state, Saturn ring and hedgehog defects were formed around the glycerol and water droplets, respectively, indicating that homeotropic anchoring was induced by adsorption of the azobenzene molecules onto the droplets. For the glycerol droplets, we observed structural transformation between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, an inter-droplet distance varied by changes of the defect size on the irradiation. These phenomena would result from modulation of anchoring conditions by the photoisomerization of the adsorbed dyes.

We investigated photochemical manipulation of physical proper-ties and colloidal structures of liquid-crystal (LC) colloids containing azobenzene compounds. In a LC suspension where polymeric particles were dispersed in a host LC, we achieved photochemical control of light-scattering properties of the suspension. In a nematic phase, when the suspension was sandwiched with two glass plates, the film became opaque. This would be attributable to an appearance of both multidomain structures of LC alignment and mismatches of refractive indices between the materials. The opaque state turned into a transparent one when a nematic-to-isotropic phase transition was induced by the trans-to-cis photoisomerization of the azo-dye. This will result from a disappearance of both the multidomain structures and the refractive-index mismatches in the isotropic phase. The transparent film went back into the initial opaque film when the nematic phase was obtained by the cis-to-trans photoisomerization. In a LC emulsion in which glycerol or water droplets were dispersed in liquid crystals, we examined photochemical change of defect structures and inter-droplet distances by the photochemical manner. At the initial state, Saturn ring and hedgehog defects were formed around the droplets. For the glycerol droplets, we observed structural transformations between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, the inter-droplet distances varied by changing defect size on the irradiation. These phenomena would result from modulation of anchoring conditions of the droplets by the photoisomerization of the azo-dyes.

A high-pressure technique is introduced which allows a continuous variation of the inclusion size in liquid crystal colloids. We use a nematic liquid crystal host into which micrometer-sized gas bubbles are injected. By applying hydrostatic pressures, the diameter of these gas bubbles can be continuously decreased via compression and absorption of gas into the host liquid crystal, so that the director configurations around a single bubble can be investigated as a function of the bubble size. The theoretically predicted transition from a hyperbolic hedgehog to a Saturn-ring configuration, on reduction of the particle size below a certain threshold, is confirmed to occur at the radius of a few micrometers.

By modulating liquid-crystal alignment on a colloidal sphere, we successfully manipulated topological defects in glycerol-droplet/liquidcrystal emulsions doped with amphiphilic, azobenzene derivatives. At an initial state, a disclination loop (Saturn ring) could be observed around the droplet, in which the azobenzene molecules should adsorb onto the droplet and liquid crystal molecules align normally to the surface of the droplet. On irradiation with ultra-violet light (lambda = 365 nm), the disclination loop was unfastened and transformed into two point defects called boojums. This should be attributed to the alignment change of the liquid crystal molecules from normal to planar arrangement triggered by trans-to-cis photoisomerization of the adsorbed azo-dyes. On irradiation with visible light causing cis-to-trans photoisomerization (lambda = 43 5 mn), the boojums went back to the Saturn ring reversibly. (c) 2005 Elsevier B.V. All rights reserved.

Our recent experiments show that the Lehmann-type rotation occurs in chiral smectic-C films in the presence of mass flux through the films and macroscopic target or spiral patterns are formed.This phenomenon is similar to that observed in Langmuir monolayers with chiral dopants [Tabe and Yokoyama, Nature Mater. 2, 806 (2003)].However, formation processes of the macroscopic patterns in these systems are different.We discuss the difference of the physical nature between these systems and propose a possible model for the dynamics of chiral smectic films.

By means of an azo-dye layer consists of Brilliant Yellow (BY), we successfully achieved an alignment control of chain-like structures formed with colloidal particles dispersed in liquid-crystals. On diagonal irradiation of the layer with unpolarized ultra-violet light, the chain-like structures exhibited an in-plane rotation toward the irradiated light. At the same time, we observed alignment change of bulk liquid crystal in a polarized optical microscope. Therefore, the photoinduced rotation of the colloidal structures will be responsible to the photoinduced alignment change of the liquid crystal molecules on the azo-dye aligning layer.

The director orientation around gas bubbles in liquid crystalline emulsions has been investigated. We introduce a new technique which allows a continuous variation of the bubble size. A nematic liquid crystal host is used into which micrometer–sized gas bubbles are injected. By applying pressure to the system, the diameter of these gas bubbles can be continuously varied. A transition from a hyperbolic hedgehog configuration to a saturn ring configuration is found when continuously decreasing the particle size. Furthermore, an electric field has been applied to the system, in order to control the director orientation around the bubbles. In addition to controlling the size of the gas inclusions, their shape can also be controlled, and long air tubes can be created.

A phenomenological model of photo-induced traveling waves in liquid-crystalline Langmuir monolayers is presented. A linear stability analysis and numerical simulations of this model reveal that there are two oscillatory unstable modes with lower and higher wavenumbers which cause the traveling waves. The unstable mode with the lower wavenumber arises due to an interplay between the spontaneous splay deformation of liquid crystal order and the anisotropic photoexcitation of molecules. The other unstable mode with the higher wavenumber is concerned with the phase separation of the concentration field induced by the spontaneous splay deformation. The numerical simulations also show the coexistence between these two modes for certain parameter values.

A phenomenological model of wave propagation in photo-excited liquid-crystal line Langmuir monolayers is constructed. The spontaneous splay deformation of the liquid-crystalline order and the anisotropy of photo-excitation of molecules are taken into account in this model. Numerical simulations of the model well reproduce qualitative features of the wave propagation phenomenon observed in recent experiments. A linear stability analysis of the model equations reveals that an interplay between the spontaneous splay deformation and the anisotropy of the photo-excitation can lead to the wave propagation. (C) 2004 Elsevier B.V. All rights reserved.

Photoinduced orientational waves in illuminated liquid-crystalline monolayers is one of the most remarkable far-from-equilibrium phenomena that systems of soft condensed matter exhibit. We model this behavior from a phenomenological point of view, taking the anisotropic photoexcitation of molecules into account. Numerical simulations as well as theoretical analyses of the model reveal that the intricate interplay between the spontaneous splay deformation of the liquid-crystalline order and the anisotropy of the photoexcitation can lead to the generation and propagation of orientational waves. The model can explain all the salient features of the phenomenon-in particular, the anomalous reversal of the propagation direction upon 90degrees rotation of the polarization direction of illumination, which evaded theoretical explanation for nearly a decade.

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.

We construct a simple phenomenological model of collective molecularrotation in chiral liquid crystal monolayers, regarding it as a 2Danalogue of Lehmann-type rotation. Results of numerical simulationsbased on this model are consistent with the experimental observationqualitatively, especially the winding/unwinding phenomena near theboundaries (defect lines, walls).

Chiral LC monolayers on glycerol surface exhibit unidirectional precession motion driven by transmembrane water tranport. The rotational speed linearly depends on both molecular chirality and mass of water transfer. The result gives a new approach to molecular motor.

Photoinduced orientational waves in illuminated liquid-crystalline monolayers is one of the most remarkable far-from-equilibrium phenomena that systems of soft condensed matter exhibit. We model this behavior from a phenomenological point of view, taking the anisotropic photoexcitation of molecules into account. Numerical simulations as well as theoretical analyses of the model reveal that the intricate interplay between the spontaneous splay deformation of the liquid-crystalline order and the anisotropy of the photoexcitation can lead to the generation and propagation of orientational waves. The model can explain all the salient features of the phenomenon—in particular, the anomalous reversal of the propagation direction upon [Formula presented] rotation of the polarization direction of illumination, which evaded theoretical explanation for nearly a decade. © 2004 The American Physical Society.

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.

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-carboocyalkoxy 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.

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 omega-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.

A phenomenological model of photo-induced wave propagation in liquid-crystalline Langmuir monolayers is constructed. The effects of the spontaneous splay deformation of liquid crystal order and the anisotropic photo-excitation of molecules are taken into consideration in this model. Most of qualitative features of the phenomenon are successfully explained by numerical simulations and theoretical analyses of the model.

Surface-specific sum-frequency vibrational spectroscopy has been used to study the structure of alkyl chains of azobenzene molecules at the air/water interface. The results show that the alkyl chains are well aligned before UV irradiation and protruding out of the surface with a certain distribution. Although the alkyl chains become less ordered by UV irradiation following dynamical motion due to cis-trans isomerization of the azobenzene core, the alkyl chains show anisotropy in the direction perpendicular to that of the azobenzene core by linearly polarized UV irradiation.

Successful attempts to manufacture synthetic molecular motors have recently been reported(1,2). However, compared with natural systems such as motor proteins(3-6), synthetic motors are smaller molecules and are therefore subject to thermal fluctuations that prevent them from performing any useful function(7). A mechanism is needed to amplify the single molecular motion to such a level that it becomes distinguishable from the thermal background. Condensation of molecular motors into soft ordered phases ( such as liquid crystals) will be a feasible approach, because there is evidence that they support molecularly driven non-equilibrium motions(8-10). Here we show that a chiral liquid-crystalline monolayer spread on a glycerol surface acts as a condensed layer of molecular rotors, which undergo a coherent molecular precession driven by the transmembrane transfer of water molecules. Composed of simple rod-like molecules with chiral propellers, the monolayer exhibits a spatiotemporal pattern in molecular orientations that closely resembles 'target patterns' in Belousov-Zhabotinsky reactions(11). Inversion of either the molecular chirality or the transfer direction of water molecules reverses the rotation direction associated with switching from expanding to converging target patterns. Endowed only with the soft directional order, the liquid crystal is an optimal medium that helps molecular motors to manifest their individual motions collectively.

We report the detailed properties of photo-induced travelling waves in liquid crystalline Langmuir monolayers composed of azobenzene derivatives. When the monolayer, in which the constituent rodlike molecules are coherently tilted from the layer normal, is weakly illuminated to undergo the trans-cis photo-isomerization, spatio-temporal periodic oscillations of the molecular azimuth begin over the entire excited area and propagate as a two-dimensional orientational wave. The wave formation takes place only when the film is formed at an asymmetric interface with broken up-down symmetry and when the chromophores are continuously excited near the long-wavelength edge of absorption to induce repeated photo-isomerizations between the trans and cis forms. Under proper illumination conditions, Langmuir monolayers composed of a wide variety of azobenzene derivatives have been confirmed to exhibit similar travelling waves with velocity proportional to the excitation power irrespective of the degree of amphiphilicity. The dynamics can be qualitatively explained by the modified reaction-diffusion model proposed by Reigada, Sagues and Mikhailov.

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.

Dialkyl-terminated smectic compounds can spontaneously spread on water surface and form stable thin films at the bulk LC temperature. Unlike the most amphiphilic Langmuir monolayers, the hydrophobic LC films undergo the layer-by-layer growth under 2D compression, from monolayer to multilayer. In the growth process, there appear some remarkable orientational structures accompanied by a point defect, which directly reveals the relation between inter-layer orientational correlation, surface anchoring and intra-layer elasticity of typical SmC phase.

A phenomenological model of wave propagation in illuminated Langmuir monolayers is constructed. Numerical simulations and theoretical analyses of this model reveal that an interplay between the spontaneous splay deformation and the anisotrpoic photo-excitation leads to the wave propagation. This model well reproduces all the qualitative features of the phenomenon.

Surface-specific sum-frequency vibrational spectroscopy has been used to study the structure of alkyl chains of azobenzene molecules at the air/water interface. The results show that the alkyl chains are well aligned before UV irradiation and protruding out of the surface with a certain distribution. Although the alkyl chains become less ordered by UV irradiation following dynamical motion due to cis-trans isomerization of the azobenzene core, the alkyl chains show anisotropy in the direction perpendicular to that of the azobenzene core by linearly polarized UV irradiation. © 2003 The American Physical Society.

In contrast to the long-held belief that only amphiphilic molecules can form stable Langmuir monolayers, we show here that even nonvolatile hydrophobic oils can be reversibly spread into liquid-condensed Langmuir films, if the material is in or close to liquid-crystal phase in the bulk. The stability origin of the hydrophobic Langmuir monolayers is entropic, rather than energetic as in the stabilization of common amphiphilic monolayers, primarily driven by the interaction between the polar head and water. This extraordinary spreading mechanism may have impact on the nature of colloidal and biomembrane stabilities.

In contrast to the long-held belief that only amphiphilic molecules can form stable Langmuir monolayers, we show here that even nonvolatile hydrophobic oils can be reversibly spread into liquid-condensed Langmuir films, if the material is in or close to liquid-crystal phase in the bulk. The stability origin of the hydrophobic Langmuir monolayers is entropic, rather than energetic as in the stabilization of common amphiphilic monolayers, primarily driven by the interaction between the polar head and water. This extraordinary spreading mechanism may have impact on the nature of colloidal and biomembrane stabilities.

A certain dialkylated achiral thermotropic nematic compound was found to exhibit a two-dimensional ferroelectric nematic, when spread on the water surface as a Langmuir monolayer. The monolayer has a larger spontaneous polarization than DOBAMBC, and shows a fast electro-optic switching with a microsecond response time under a low electric field.

We describe the results of a detailed study of two-dimensional (2D) smectic-C to solid-like phase transition in azobenzene-derivative Langmuir monolayers by the surface pressure vs area-per-molecule isotherm measurement, polarizing optical microscopy, and the grazing incidence synchrotron x-ray diffraction. The phase transition was observed to be weakly first order up to slightly above room temperature with a transition entropy less than 1.0 k(B) per molecule, accompanied by proper characteristics of a nearly ideal horizontal coexistence line on the isotherm, an abrupt change in optical texture, and the emergence of a conspicuous x-ray diffraction peak in the solid-like phase, which indicates a weak positional order with a correlation length of 10-20 nm. Analysis of the x-ray diffraction data within the framework of distorted hexagonal lattice suggests that the solid-like phase may be regarded as a 2D analog of smectic-L phase that is a hexatic smectic phase with the molecules tilted toward a direction between the nearest and the next-nearest bonds. At higher temperatures, the transition became less discontinuous and entirely disappeared above 40 degreesC in all these experimental aspects. We argue that the transition is viewed as a 2D induced hexatic-hexatic transition (analog of smectic-C to smectic-L transition), which has an isolated critical point where the first-order transition comes to an end. (C) 2001 American Institute of Physics.

Some thermotropic liquid crystal molecules are known as they can form stable Langmuir monolayers on air-water interface. However, prerequisites for formation of such a Langmuir monolayer are not well understood yet except some molecules (e.g. cyano-biphenyl derivatives). We apply a molecular simulation approach to study this subject with special attentions on the liquid crystal - water interactions in the Langmuir monolayers.

Two-dimensional Isotropic-Smectic C phase transition is observed for the first time in Langmuir monolayers composed of dialkyl-terminated thermotropic LC compound. Under the 2D compression, the monolayers exhibit the first-order phase transition from isotropic fluid, where the constituent molecules lie down on the water surface, to the 2D SmC phase. The transition is completely reversible with a clean indication the SmC order induced by the 2D compression in the monomolecular films.

Molecular dynamics simulations of simple models of Langmuir layers are conducted. Softcore spherocylinders interacting via repulsive interaction along with simple force models of water-molecule interaction give rise to SmC phase (titled phase) layer. This suggests that SmC layers can appear in substance without thermotropically stable SmC phase in bulk. Simulation results also suggest that SmC layers might appear in the temperature range where nematic LC is stable in bulk, Dynamics as well as microscopic properties are reported.

It has been shown experimentally that molecules, which exhibit liquid crystal phases in bulk, also show interesting phenomena when they are formed in monolayers at air-water interface. The purpose of this work is to clarify to what extent can a simple model explain the complicated behavior of such Langmuir monolayers. Molecular dynamic simulation is conducted to observe the phase and dynamics of Langmuir monolayers.

Certain class of amphiphilic derivatives of azobenzene form a stable monolayer analog of single-layer smectic-C (SmC) phase at the air-water interface. Due to the broken up-down symmetry, this two-dimensional liquid crystal shows intriguing static orientation structures such as the stripe and higher-order point defects in equilibrium. We found that weak excitation of isomerization reaction of azobenzene core results in a persistent generation of orientational waves and solitons propagating in the plane of the monolayer. This is the first example of purely light-driven nonequilibrium pattern formation. Analysis of the static structures has revealed the essential significance of the coupling between the orientational order and molecular density. Although no definite explanation as yet exists for the dynamic behavior, we believe the density-orientation coupling should play an important role.

New tilted smectic phases in Langmuir monolayers composed of FLC materials are reported in this paper. We found a mixture of several FLC materials take 2D SmC phase on the water surface at room temperature, showing similar schlieren texture to bulk SmC and nematics. Under compression, unlike the ordinary Langmuir monolayers, the film exhibits first-order monolayer-by-monolayer growth of the film thickness on the water surface, eventually resulting in multilayer-structures instead of collapsing.

The alleged in-plane polar structure in two-dimensional (2D) smectic-C liquid crystalline phases of Langmuir monolayers was directly confirmed by the optical second harmonic generation (SHG) spectroscopy for the first time. The SH signal associated with the in-plane polar structure was found to be comparable with that coming from the out-of-plane polar distribution of molecular orientation inherent at the air-water interface, This result indicates that there exits a strong preference for the heads and tails of the molecules to spontaneously associate one another over the otherwise isotropic water surface as a result of the 2D liquid crystalline order. When the monolayer underwent a first order phase transition from SmC to a solid-like phase under compression, both of the in-plane and out-of-plane components of SH signals were considerably reduced despite an increase in density, implying the rather subtle nature of the centro-symmetry breaking in the SmC phase.

We carried out the first quantitative measurements of correlated modulations of molecular tilt and azimuthal angles in two-dimensional smectic-C Langmuir monolayers using simultaneous linear- and circular-polarized reflected light microscopy. For spontaneously formed stripes and higher-order point defects, the tilt angle varies nearly sinusoidally at twice the spatial frequency of the azimuthal rotation. The tilt modulation grows as the second power of the modulation wave number and leads to a large escaped core for the point defect. Our results can be explained by an extended Landau theory of tilted smectics.

Simultaneous use of linear- and circular-polarizing reflected light microscopes allowed first quantitative observation of correlated modulations of molecular tilt and azimuthal angles in two-dimensional (2D) smectic-C Langmuir monolayers. For spontaneously formed stripes and higher-order point defects, the tilt angie varied nearly sinusoidally with twice the spatial frequency of the continuous azimuthal rotation. The tilt modulation grew as the second power of the modulation wavenumber and led to a large escaped core for point defects. These results can be consistently explained by an extended Landau theory of tilted smectics.

We have developed a phenomenological order-parameter theory of photo-induced reorientation in liquid crystals. With an assumption of rapid rotational diffusion of photo-excited molecules, the effective photo-induced torque on the director has been formulated in a simple closed form in terms only of the tensor order parameters of the ground state and excited dye molecules. In particular, the torque is proportional to the difference of these order parameters and, accordingly, changes sign depending on the relative magnitude of the order parameters. Illumination effect on the Freedericksz transition is proposed to be a convenient experimental scheme to quantitatively study the reorientation behavior. Supporting experimental demonstration will be presented.

We studied orientational fluctuations in a smectic-C Langmuir monolayer. Our measurements of orientational correlations are in excellent agreement with theoretical predictions. In addition, we present the first measurements of orientational elasticity and viscosity in a two-dimensional system whose density can be varied. The orientational viscosity strongly depends on temperature and density, changing by more than an order of magnitude with a 2.5% increase in temperature or a 20% change in density. The orientational elasticity is only weakly dependent on temperature and density.

Purely light-driven spatiotemporal pattern formation has been found to take place in a liquid-crystalline Langmuir monolayer consisting of an amphiphilic azobenzene derivative, undergoing the trans &lt;----&gt; cis photoisomerizations. The Langmuir monolayer is in a smectic-C-like liquid crystal phase, whose two-dimensional orientation is easily perturbed by slight conformation changes in the constituent molecules. On illumination with a linearly polarized light, a collective and global in-plane reorientation of the azobenzene chromophores is induced over an existing static stripe texture, which finally yields polarization-dependent steady state orientational patterns. Prolonged photoexcitation generates sustained traveling and solitary waves, associated with variations in molecular tilt directions. The liquid crystallinity of the monolayer allows these orientational responses to occur even at an extremely weak light power at least 2 orders of magnitude smaller than that known in previous photoreorientation studies of azobenzene chromophores.

An approximate yet highly accurate Fresnel formula, describing the reflection from optically anisotropic Langmuir monolayers, is derived in a simple closed form. The utility of the Fresnel formula is demonstrated by an application to Brewster angle microscopy.

Depolarized Brewster-angle microscopy revealed a novel two-dimensional (2D) mesophase in Langmuir monolayers of 4-octyl-4'-(3-carboxytrimethyleneoxy) azobenzene, characterized by ubiquitous schlieren textures resulting from the long-range order of in-plane molecular orientations. The lack of half-integral strength disclinations and the presence of a regular array of pi-walls, across which the in-plane orientation changes by 180 degrees, indicate the vectorial nature of the underlying order parameter. The monolayer can, therefore, be viewed as a single layer of a bulk smectic C phase or as a 2D polar nematic phase, except for the obvious absence of mirror symmetry with respect to the layer plane. In contrast to the experience with bulk liquid crystalline phases, higher-order point disclinations were often found stable in the monolayer.

Surface-stabilized ferroelectric liquid crystal was aligned by the self-assembled monolayers (SAMs) of amphiphilic diacetylene derivatives formed on an indium tin oxide/glass substrate to maintain bistability when ferroelectric liquid crystal with high spontaneous polarization was used. The SAMs were disposed uniaxially either after rubbing them or passing them through a meniscus at a three-phase contact between a substrate, air, and n-hexane before exposing them to ultra-violet (UV) light. Infrared transmission spectra, contact angles against water and time of flight secondary ion mass spectra have revealed that the modified surface was a sparse monolayer of the diacetylenes, and that they were polymerized by UV light.

The angular distribution function of rodlike particles in Langmuir-Blodgett (LB) films is numerically analyzed. The calculation is based on the integral form of the rotatory diffusion equation and, in contrast with previous analyses, does not assume an instantaneous thermal equilibrium. As each particle keeps memory of the flow history on the water surface, the final distribution function is dependent on the initial conditions of the particle. However, when-the initial point is so far from the substrate that the memory of initial point is almost lost, the final distribution function is approximately determined by the dimensionless number C = (zeta'G+tau0)/2k(B)T, where zeta' is the rotational friction coefficient, tau0 the Bingham yield value, a the substrate width, and nu(d) the dipping velocity of the substrate. The presence of a meniscus region around the substrate should be taken into account. The streamlines between the water surface and the substrate surface are smoothly connected, while assuming a cylindrical shape for the meniscus. The angular distribution function obtained by this numerical calculation is in good agreement with the experimental results for a mixed LB system of merocyanine dye/fatty acid.

We measured the frequency dependence of the longitudinal viscosity and the layer compression modulus of homeotropically aligned multilamellar film of hydrated dimyristoyl phosphatidylcholine (DMPC) at low frequencies from 10 Hz to 1 kHz, varying temperature (T) and relative humidity (RH) systematically. We have, for the first time, demonstrated unambiguously that in the L(alpha) phase (the lyotropic smectic-A phase) the longitudinal viscosity diverges as 1/omega when the circular frequency goes to zero. In addition, we were able to construct the T-RH phase diagram of the L(alpha)-L(beta') transition of hydrated DMPC, based upon the T and RH dependences of the layer compression modulus. The phase boundary thus determined agreed well with that obtained by X-ray scattering by Smith et al. (J. Chem. Phys. 92 (1990) 4519).

The occurrence of flow orientation during the deposition of Langmuir-Blodgett films of (TMTTF)3(C14TCNQ)2 is shown through studies of in-plane molecular orientation in films deposited by two types of the vertical dipping method, with the substrates parallel and perpendicular to the barrier, using ESR and polarized UV-visible spectroscopies. Larger in-plane anisotropy is observed toward the edge of the substrates, which is consistent with the prediction of the recent theory of flow orientation during the deposition process. Furthermore, in-plane anisotropy in the films deposited by the horizontal lifting method is detected, suggesting the existence of a compression orientation at the air-water interface.

Stable radical species existing in mixed Langmuir-Blodgett films of a merocyanine dye and arachidic acid are studied through their hyperfine couplings using the isotope substitution technique. One of the species shows a nitrogen hyperfine structure possibly arising from one of the two nitrogen sites in the molecule. With the employment of two dye analogs in which either one of the N-14 nuclei is replaced by N-15, the observed nitrogen site has been identified to be the one in benzothiazole. That is, the wave function of the radical is directly associated with the dye chromophore. The photo-induced spectra have shown a similar change as the dark spectra upon N-15-substitution, indicating that the dark and photo-induced signals arise from a common species. These facts together with the recently observed correlation between the anisotropic behaviour of ESR and optical J-band strongly suggest an intermolecular charge transfer in J-aggregates as the origin of radical generation.

The angular distribution function for the case of one single substrate in a large trough is numerically calculated allowing for the deviation from the local thermal equilibrium. The function obtained for the line-sink potential on the water surface is found to disagree with that of the previous model derived using the local thermal equilibrium approximation. As for the transfer from the water surface to the substrate, two different models are introduced, the abrupt connection and a smooth connection. The smooth connection model leads to a satisfactory agreement with the predictions from the previous model, and, at the same time, to a semi-quantitative coincidence with the experimentally observed dichroic behavior for the previously obtained values of the viscoelastic parameters. These results indicate that the line-sink potential with local thermal equilibrium approximation, if not strictly relevant to the process on the water surface, is effective for describing the angular distribution in LB films.

The molecular orientation in Langmuir-Blodgett films of a 3:2 charge-transfer complex of tetramethyltetrathiafulvalene and tetradecyltetracyanoquinodimethane [(TMTTF)3(C14TCNQ)2] is discussed from the observed anisotropic ESR spectra at the K and X bands. Anisotropy of g values shows the existence of in-plane preferential orientation of the complex with the p-pi-orbital axis and long axis of the TMTTF molecules parallel and perpendicular to the dipping direction of the substrate, respectively. The effect of aging on ESR spectra of the system is also reported. The decrease in the difference in linewidth at the K and X bands observed for the external magnetic field normal to the film plane indicates the reduction in the degree of misorientation of the molecules by aging.

Interface-adsorbed complex Langmuir-Blodgett (LB) films of arachidic acid and water-soluble, mesosubstituted cyanine dyes were fabricated using the diffusion-adsorption method to examine the substituent-dependent self-assembly at the water-monolayer interface. Either a J aggregate or an H aggregate was found to be formed in the LB films depending on the substituent introduced, the ethyl or methyl group. The H aggregate is accompanied by Davydov splitting, which is characterized as the split of the band into two bands, whose transition moments are orthogonal to each other. Measurements of photoluminescence and microscopic spectroscopy were performed to identify the type of the aggregates. The molecular arrangements in the aggregates were estimated based on Davydov's theory and the extended dipole model. Dependence of photoelectric properties of the LB films on the type of aggregates has been studied employing Schottky-type cells.

The in-plane anisotropy of the Langmuir-Blodgett films of a merocyanine-fatty acid mixed system has been further studied for two different cases of batch production with the substrates aligned face to face and side by side, respectively, to clarify the limitations of the flow-orientation model based on the ideal-fluid approximation. For the side-by-side case, satisfactory coincidence is found between the model and experiment. The actual dichroic behavior deviates from that predicted for the face-to-face case with smaller intersubstrate distances. It was speculated that the stagnation point is associated with anomaly in velocity which is responsible for this discrepancy. In order to examine this, the flow of the monolayer on the water surface during the deposition has been observed using sulphur powder as marker in addition to the optical measurements. The actual flow deviates from that expected from the model and is associated with unsteady motion around the stagnation point as previously speculated. It is indicated that the ideal-fluid approximation is inappropriate for the face-to-face case with smaller distances, leading to the prediction inconsistent with the actual dichroic behavior.

Interface-adsorbed complex Langmuir-Blodgett (LB) films of arachidic acid and a water-soluble cyanine dye were fabricated using the diffusion-adsorption method. Formation of an H-aggregate with absorption band split was observed in the LB film. This split is assignable as Davydov splitting, which is characterized as the split of the band into two bands, whose transition moments are orthogonal to each other, due to formation of herringbonelike aggregates. The estimation of the molecular arrangement in the aggregate was performed based on Davydov's theory and the extended dipole model.

Water-soluble cyanine dye derivatives can be adsorbed from aqueous solution to an arachidic acid monolayer at the air-water interface. Interface-adsorbed complex Langmuir-Blodgett films of arachidic acid and four different derivatives of thiacarbocyanine dyes were fabricated using this method, and their optical properties were examined employing a linearly polarized incident. Clear differences in both spectral shape and in-plane anisotropy were found among the films of different derivatives, each associated with an aggregate form characteristic of the substituent group. They can be classified as a dimer with Davydov splitting, a monomer, and a J aggregate. Estimation of the configuration of the molecules in the dimers and measurement of the photoluminescence spectrum for the J aggregate were performed to clarify the nature of aggregates. The results suggest the possibility of systematic control of aggregate formation in the system by introducing substituent groups for dyes.

The liberation process of metal ions in fatty acid salt LB films soaked in a dilute hydrochloric acid has been studied using X-ray diffraction and IR measurements. The reaction kinetics was found to be described as a pseudomonomolecular reaction. It is suggested that the metal ions, after being liberated from the carboxylate sites, are removed from the film system into the solution.

Two kinds of stable radical species exist in mixed Langmuir-Blodgett (LB) films of a merocyanine dye and arachidic acid. One of the species exhibits clear nitrogen hyperfine structure in ESR spectra, which was previously confirmed by measurements at X and Q bands. Use of the N-15-enriched dye derivative clearly identified the hyperfine coupling to arise from the nitrogen nucleus in benzothiazole, which belongs to the chromophore of the dye molecule; N-C = C-C = C-C = O. ESR spectra measured at both X and K bands in unsubstituted and N-15-substituted systems permits the detailed analysis of in-plane molecular orientation using the spectrum-simulation method incorporating three-dimensional freedom of orientation. The analysis of the dependence of the spectra on the substrate position yields the local orientation of the radical molecules, which shows a higher degree of orientation toward the edge of the substrate. This behavior coincides with that of the majority of molecules forming J aggregates, obtained from optical analysis, and is well described by a recent theory of the flow orientation of molecular domains caused during the dipping process of LB films. This coincidence between the orientation of the radicals and J aggregates provides new evidence that stable radicals are generated in the J aggregate. The mechanism of radical generation is discussed in view of our previously proposed model of an intermolecular charge transfer in J aggregates.

ESR measurements were performed on Langmuir-Blodgett (LB) films of 1:2 complex of long-chain pyridinium and TCNQ, where the long chain contains photo-active azobenzene group. Observed temperature dependence of the spin susceptibility is consistent with the formation of the random-exchange Heisenberg antiferromagnetic chains in the system.