Akihiko Sugimura

Also recognized as carbohydrate liquid crystals, glycolipids are amphiphiles whose basic unit comprises of a sugar group attached to an alkyl chain. Glycolipids are amphitropic, which means these materials form liquid crystal self-assemblies when dry (thermotropic) as well as when dissolved in solvents (lyotropic/surfactants) such as water. Many glycolipids are also naturally derived since these can be found in cell membranes. Their membrane and surfactant functions are largely understood through their lyotropic properties. While glycolipids are expected to play major roles as eco-friendly surfactants in the global surfactant market, their usefulness as thermotropic liquid crystal material is, to date, unknown, due to relatively lack of research performed and data reported in the literature. Understandably since glycolipids are hygroscopic with many hydroxy groups, removing the last trace water is very challenging. In recent time, with careful lyophilization and more consistent characterization technique, some researchers have attempted serious studies into “dry” or anhydrous glycolipids. Motivated by possible developments of novel thermotropic applications, some results from these studies also provide surprising new understanding to support conventional wisdom of the lyotropic systems. Here we review the dry state of glycosides, a family of glycolipids whose sugar headgroup is linked to the lipid chain via a glycosidic oxygen linker. The structure property relationship of both linear and anhydrous Guerbet glycosides will be examined. In particular, how the variation of sugar stereochemistry (e.g. anomer vs. epimer), the chain length and chain branching affect the formation of thermotropic liquid crystals phases, which not only located under equilibrium but also far from equilibrium conditions (glassy phase) are scrutinized. The dry glycolipid assembly has been subjected to electric and magnetic fields and the results show interesting behaviors including a possible transient current generation.

A static deuterium nuclear magnetic resonance ((HNMR)-H-2) technique (magnetic field, B = 7.05 T) was employed to monitor the thermotropic lamellar phase of the anhydrous 1:1 mixture sample of octyl-b-D-glucoside (beta OG) and that of partially deuterium labelled at the alpha position on the chain, i.e., beta OG-d(2). In the absence of an electric field, the H-2 NMR spectrum of the mixture gives a typical quadrupolar doublet representing the aligned lamellar phase. Upon heating to beyond the clearing temperature at 112 degrees C, this splitting converts to a single line expected for an isotropic phase. Simultaneous application of magnetic and electric fields (E = 0.4 MV/m) at 85 degrees C in the lamellar phase, whose direction was set to be parallel or perpendicular to the magnetic field, resulted in the change of the doublet into a single line and this recovers to the initial doublet with time for both experimental geometries. This implies E- and B-field-induced phase transitions from the lamellar to an isotropic phase and a recovery to the lamellar phase again with time. Moreover, these phase transformations are accompanied by a transient current. A similar observation was made in a computational study when an electric field was applied to a water cluster system. Increasing the field strength distorts the water cluster and weakens its hydrogen bonds leading to a structural breakdown beyond a threshold field-strength. Therefore, we suggest the observed field-induced transition is likely due to a structure change of the (ss)OG lamellar assembly caused by the field effect and not due to Joule heating.

There have been many investigations of the alignment of nematic liquid crystals by either a magnetic and/or an electric field. The basic features of the important hydrodynamic processes for low molar mass nematics have been characterized for the systems in their equilibrium and non-equilibrium states. These have been created using electric and magnetic fields to align the director and deuterium nuclear magnetic resonance (H-2 NMR) spectroscopy has been used to explore this alignment. Theoretical models based on continuum theory have been developed to complement the experiments and found to describe successfully the static and the dynamic phenomena observed. Such macroscopic behaviour has been investigated with H-2 NMR spectroscopy, in which an electric field in addition to the magnetic field of the spectrometer is used to rotate the director and produce a non-equilibrium state. This powerful technique has proved to be especially valuable for the investigation of nematic liquid crystals. Since the quadrupolar splitting for deuterons observed in the liquid crystal phase is determined by the angle between the director and the magnetic field, time-resolved and time-averaged H-2 NMR spectroscopies can be employed to investigate the dynamic director alignment process in a thin nematic film following the application or removal of an electric field. In this article, we describe some seminal studies to illustrate the field-induced static and dynamic director alignment for low molar mass nematics. (C) 2016 Elsevier B.V. All rights reserved.

We applied density functional theory to study octyl-D-xyloside isomers in order to explain the features responsible for the liquid crystal mesophases. Compared to a glucoside, the xylose headgroup has a proton instead of the hydroxymethyl group on C5. Thus, a xyloside has a reduced headgroup volume that renders it less hydrophilic. Our results have shown that the xylose headgroup may adopt stable pyranose and furanose conformations, which may lead to different effective headgroup hydrophilicities. These features are probably responsible for forming two non-equivalent inverse micelles, which are self-assembled into a cubic discontinuous phase with a space group of Fd3m commonly found for xylosides. While different factors are responsible for controlling the relative stability of each isomer, the role of intramolecular hydrogen bonding was highlighted for the investigated single molecule. The polarisable continuum model was used to take into account the solvent effect in order to understand the molecular behaviour in very polar systems. Results from calculations carried out in gas phase were used for comparative purposes. The molecular electrostatic potential calculations for these xylolipids demonstrate sugar amphoterism, which is implicated in the heterogeneity nature of lipid self-assembly. [GRAPHICS]

The dynamic alignment of the nematic director by near-orthogonal electric and magnetic fields has been investigated. The intermediate states during the relaxation process were found, with the aid of time-resolved deuterium NMR spectroscopy, to be markedly nonuniform. The macroscopic order was perturbed, although the initial and final states of the director appear to be essentially uniform. However, the initial state does have a profound influence on the uniformity of the director in the intermediate states. We have developed a fundamental model based on the effect of spontaneous director fluctuations to explain these unusual NMR observations.

Vesicles formed by self-assembly of lipids and surfactants are increasingly recognised as carriers for drug delivery applications in disease targeting and many other biomedical-related areas, demonstrable by the growing number of significant publications. This manuscript reviews important facets of lipid-based vesicles as drug carriers and their surface modifications to achieve controlled release and selective cell targeting. We cover both the more commonly used ionic phospholipid vesicle carriers and the rapidly growing field of non-ionic vesicles/niosomes using self-assembly of uncharged amphiphilic molecules, which could be formed by using sugar surfactants or glycolipids, sorbitan esters, and polyoxyethylene alkyl ethers. Due to their lower cost, biodegradability, low-toxicity, low-immunogenicity and specific sugar-cell recognition, much attention would be devoted to glycolipid bio-surfactants as potential carriers for targeted delivery. Specifically, our review points to the design consideration of lipid and surfactant nano-carriers based on critical packing parameter, membrane curvature, and the effects of hydrophobic chain structures. We have also dedicated a section of this review to summarise some novel applications of various lipid liquid crystal phases in drug delivery, and how in turn these are related to chemical structures of the lipid entities. The final section of this review outlines the application of lipid vesicles as delivery agents for diagnostic imaging.

The director dynamics for a low molar mass nematic liquid crystal (LC) has been investigated theoretically based on the hydrodynamic theory including the director motion. Analysis of the numerical results for the turn-on process provides an evidence for the appearance of the spatially periodic patterns in 4-n-pentyl-4′-cyanobiphenyl LC film, only in response to the suddenly applied strong electric field orthogonal to the magnetic field. It has been shown that at the values of the voltage in 200 V across the 194.7 μm LC film and the magnetic field of 7.05 T directed at the angle α = 1.57(~ 89.99) between two fields there is the threshold value of the amplitude of the thermal fluctuations of the director over the LC sample which provide the nonuniform rotation mode rather than the uniform one, whereas the lower values both of the amplitude and the angle α (&lt 1.565(~ 88.81)) dominate the uniform mode. During the turn-off process, the reorientation of the director to its equilibrium orientation is characterized by the complex destroying of the initially periodic structure to a monodomain state. © 2013 Elsevier B.V.

We have investigated the phase behavior of four glycosides (beta C(8)OGlc, beta C(8)SGlc, beta C(10)OGlc, beta C(8)OGal) in water and D2O by optical polarizing microscopy and deuterium NMR. Previously published phase diagrams were evaluated by deuterium NMR, via monitoring D2O spectra, and confirmed the presence of the hexagonal, bicontinuous cubic, and lamellar phases in these glycosides. We have also shown the presence of the gel phase in (beta C(10)OGlc) and observed the extensive supercooling of the lamellar phase to temperatures well below the Kraft line. While the main features of the phase diagrams were confirmed, some phase boundaries were found to be slightly different. Magnetically aligned spectra were also observed for relatively dilute samples for the hexagonal phase (beta C(8)OGlc and beta C(8)OGal) and the lamellar phase (beta C(8)SGlc and beta C(10)OGlc). The average number of bound water molecules per headgroup in the lamellar phase for the glycosides was determined by the systematic measurement of the quadrupolar splitting of D2O over a wide range of values of the (glycoside/water) molar ratio. The number of water molecules bound to the headgroup was found on average to be about 1.6-1.7 water molecules with no significant differences in this value for the different glycosides (and over the temperature range investigated), indicating that the bound water content is predominately influenced by the number of hydroxyl groups of the headgroup only. However, this bound water content of only 1.6-1.7 water molecules per sugar headgroup is surprisingly low, suggesting strong intermolecular interactions of the OH groups of headgroup sugars. The results are in line with computational results reported earlier for the octyl-beta-glucoside and beta-galactoside, which show the presence of strong intralayer hydrogen bonding.

There have been many investigations on the alignment of nematic liquid crystals by either a magnetic and/or an electric field. The basic features of these important hydrodynamic processes have been characterized for systems in their equilibrium and non-equilibrium states. To complement the experiments, theoretical models based on continuum theory have been developed, which successfully describe the static and dynamic phenomena. Such macroscopic behavior has been investigated with deuterium nuclear magnetic resonance (DNMR) spectroscopy, in which the electric field, in addition to the magnetic field of the spectrometer, is used to rotate the director and produce a non-equilibrium state. This powerful technique has proved to be especially important in the investigation of liquid crystals. Since the quadrupolar splitting for deuterons observed in the liquid crystal phase is determined by the angle between the director and the magnetic field, time-resolved DNMR spectroscopy has been employed to investigate the dynamic director alignment process in a thin nematic film following the application or removal of an electric field. In this article, we describe illustrative key studies of field-induced director orientations for low molar mass nematics using DNMR with an electric and a magnetic field to align the director.

This work describes an investigation of the static (or quasistatic) nuclear magnetic resonance (NMR) response in a nematic liquid crystal confined between two planar conducting plates and subject to a magnetic field and an electric field produced by a difference of voltage applied on the plates. Deuterium NMR spectroscopy of 4-pentyl-d(2)-4'-cyanobiphenyl (5CB-d(2)) under these conditions has revealed a voltage dependent inhomogeneous director distribution for a particular narrow range of voltages and for a fixed magnetic field (that of the spectrometer). In the ideal setup the two plates are assumed to be rigorously parallel, so that a difference of voltage applied on the plates leads to a constant electric field normal to them. When the magnetic field is parallel to the plates (orthogonal geometry) there exists a threshold value of the electric field for which the effect of both fields exactly compensate; moreover, for stronger electric field the director aligns with the electric field while for weaker electric field the director aligns with the magnetic field. If there is a lack of parallelism between the two plates, the electric field becomes inhomogeneous so that it may be larger than the threshold value in some region of the sample and smaller in the remaining part of the sample. In that case the director will adopt essentially two orientations within the sample, namely, parallel or perpendicular to the magnetic field, and the position of the frontier between the two domains depends on the voltage. This feature is clearly shown by deuterium NMR spectra that exhibit a transfer of intensity between two quadrupolar doublets with increase in the applied voltage. The coexistence of two director populations occurs for a range of voltages that depends on the degree of nonparallelism; accordingly, an estimation of this range by NMR yields an experimental estimation of the lack of parallelism. A tiny tilt of the magnetic field (nonorthogonal geometry) entrains a notably different behavior since a single doublet with voltage dependent splitting is observed in this case. In a first stage (simple model) of this work, the main features observed for the orthogonal and nonorthogonal geometries are interpreted within the framework of Leslie-Ericksen theory by employing the concept of a single effective field replacing the two real fields. However, the spectra reveal an additional director distribution, especially for the orthogonal geometry, that cannot be interpreted by this simple approach. In a second stage (advanced model), these less clear features have been investigated by numerical simulations of a two-dimensional model which includes the effects of inversion walls and of the high relative dielectric anisotropy of 5CB.

Anomers and epimers alpha- and beta-gluco and -galactosides are expected to behave differently. However, recent results on a series of Guerbet glycosides have indicated similar liquid crystal clearing temperatures for pure p-glucosides and the corresponding alpha-galactosides. This observation has led to speculation on similarities in the self-assembly interactions between the two systems, attributed to the trans-configuration of the 4-OH group and the hydrophobic aglycon. Previous simulations on related bilayers systems support this hypothesis, by relating this clearing transition temperature to intralayer (sugar-sugar) hydrogen bonding. In order to confirm the hypothesis, the comparison was expanded to include the cis-configurated pair, that is, alpha-gluco/beta-galactoside. A set of alpha-configurated Guerbet glucosides as well as octyl alpha-galactoside were prepared and their thermotropic phase behavior studied. The data obtained enabled a complete comparison of the isomers of interest. While the results in general are in line with a pairing of the stereo-isomers according to the indicated cis/trans-configuration, differences within the pairs can be explained based on the direction of hydrogen bonds from a simple modeling study. (C) 2011 Elsevier Ltd. All rights reserved.

The peculiarities in the dynamic of the director reorientation in a liquid crystal (LC) film under the influence of the electric E field directed at an angle alpha to the magnetic B field have been investigated both experimentally and theoretically. Time-resolved deuterium NMR spectroscopy is employed to investigate the field-induced director dynamics. Analysis of the experimental results, based on the predictions of hydrodynamic theory including both the director motion and fluid flow, provides an evidence for the appearance of the spatially periodic patterns in 4-n-pentyl-4'-cyanobiphenyl LC film, at the angles alpha > 60 degrees, in response to the suddenly applied E. These periodic distortions produce a lower effective rotational viscosity. This gives a faster response of the director rotation than for a uniform mode, as observed in our NMR experiment.

Time-resolved NMR spectroscopy is a powerful method to investigate field-induced rotation of the director in a nematic liquid crystal. The method requires that the director does not rotate significantly during the acquisition of the free induction decay and hence the NMR spectrum. We have extended the method to systems where this is not the case and the observed NMR spectra are now found to contain novel oscillatory features. To understand these oscillations, we have developed a model combining both director and spin dynamics. In addition to increasing the information content of the time-resolved NMR spectra, it also proves possible to determine the field-induced relaxation time from a single spectrum.

The static director distribution in thin nematic liquid crystal cells, subject to both electric and magnetic fields, has been investigated using a combination of deuterium nuclear magnetic resonance (NMR) spectroscopy and continuum theory in terms of the director distribution function, which gives the probability density for finding the director at a given orientation. A series of deuterium NMR spectra for the nematic liquid crystal, 4-pentyl-d(2)-4'-cyanobiphenyl deuteriated in the alpha position of the pentyl chain were acquired as a function of the applied electric field. This powerful experimental technique allowed us to observe uniform and nonuniform director alignment depending on the angle between the two fields and their relative strength. On the basis of the detailed experimental results, we have explored the factors that influence the nature of both the uniform and the nonuniform director distributions. We have discussed the questions that are raised by our attempt to understand the static director distribution as a function of the angle between the two fields. We have discovered that the alignment of the director at the surface of the Teflon spacers is essential in addition to the random variation in the cell thickness in order to account for the static director distribution determined from the NMR spectra.

Deuterium NMR spectroscopy is widely employed to investigate the static and dynamic director alignment for low molar mass nematics contained in a thin sand-wich cell. When the director is not uniformly aligned the appearance of the deu-terium NMR spectra, recorded in the measurements, reflects the form of the director distribution. This occurs because the observed spectrum is a weighted sum of the spectra from all director orientations in the sample. In order to obtain the form of the director distribution function by simulating the spectra it is necessary to know how the spectral lineshape varys with the director orientation. As well as being of practical relevance, when the director distributes thermally with the average director orientation in multi domains, this contribution to the lineshape is of funda-mental interest for nematic behaviour.

The longitudinal (spin-lattice) relaxation in nuclear magnetic resonance (NMR) experiments on 4-n-pentyl-4'-cyanobiphenyl (5CB) mesogen, deuteriated in the alpha-position, has been investigated by changing the orientation of the phase director with respect to the instrumental magnetic field through the application of a competing alternating electric field. The angular-dependent profiles of the corresponding rotational spectral densities were fitted and interpreted by invoking a model for single-molecule reorientational dynamics and fluctuations of the local director with respect to the average direction of alignment. The relative contribution of the two processes to the longitudinal relaxation rate has been estimated, and values of the principal components of the rotational diffusion tensor of the 5CB molecule were obtained from the data fit. The work focuses mainly on the methodological grounds, by pointing out the increase in the extent of achievable information when passing from standard NMR experiments performed at the canonical orientation of the sample (that is an alignment collinear to the magnetic field) to measurements on arbitrarily oriented samples.

Surface relief gratings on organic polysilane thin films are fabricated by holographic exposure of ultra-violet light, and Au gratings are subsequently prepared on polysilane gratings by vapor deposition of Au. The anchoring energies of 4-pentyl-4’-cyanobiphenyl (5CB) nematic liquid crystal on the fabricated gratings are determined with a saturation voltage method. The anchoring energies of Au gratings are weaker than those of organic polysilane gratings because of suppression of π?π interaction between the liquid crystal and the alignment layer. The polar anchoring energies of Au gratings are also weaker than those reported in literature.

Deuterium NMR spectroscopy is widely employed to investigate the<br /> static and dynamic director alignment for low molar mass nematics <br /> contained<br /> in a thin sandwich cell. When the director is not uniformly aligned the<br /> appearance of the deuterium NMR spectra, recorded in the measurements,<br /> reflect the form of the director distribution. This occurs because the<br /> observed spectrum is a weighted sum of the spectra from all director<br /> orientations in the sample. In order to obtain the form of the director<br /> distribution function by simulating the spectra it is necessary to know <br /> how<br /> the spectral linewidths vary with the director orientation. As well as<br /> being of practical relevance, the angular dependence of the linewidths is<br /> of fundamental interest for nematic behaviour because it is related to<br /> factors such as molecular rotation, director fluctuations and <br /> orientational<br /> order. Here we explore ways to vary the director orientation, as a<br /> monodomain, using an electric field and employ this to measure the angular<br /> dependence of the NMR linewidths for the nematic phase of<br /> 4-α,α-d2-pentyl-4′-cyanobiphenyl as a function of temperature.

Film thickness dependences of the unified surface anchoring strengths from the splay deformation for nematic cells were discussed. Thin <br /> nematic parallel (d =2–50 μm) and wedge (d = 0.3–5 μm) cells with the same solid surface were prepared to evaluate the surface anchoring <br /> strength. The surface anchoring strengths from the splay deformations for two kinds of liquid crystals were measured by using the saturation <br /> method. The nematogens used were 4-pentyl-4′-cyanobiphenyl and mixture compound ZLI-4792 (Merck Japan Co., Ltd.) with positive dielectric <br /> anisotropy. Film thickness dependence of the surface anchoring strength was elucidated on the basis of the conventional ionic surface polarization. <br /> It was also discussed that a surface anchoring strength from the splay deformation is to be an intrinsic value defined at an interfacial region and not <br /> a value changing with the film thickness.

Functional director alignment layers are needed for high performance liquid crystal displays (LCDs). Reported herein is a novel polymer material for LC alignment, namely perfluoropolyether (PFPE), which exhibits weak surface anchoring energy for bend deformation and is amenable to simple fabrication of grooved surfaces by softlithography, a surface topography desired for multi-stable LCDs. Liquid crystal optical cells fabricated using Langmuir-Blodgett films of PFPE (of variable thickness) exhibited weak surface anchoring energies on the order of 10-5 J/m2 for the nematic liquid crystal 4-cyano-4’-pentyl-1,1’-biphenyl (5CB) with no dependence on film thickness.

人々の生活をより豊かにすることの出来る安心で身近な質の高いエレクトロニクス技術に関心が集まっている。そのためには、ソフトで軽量な有機材料をエレクトロニクス機器の中で自在に活用することが是非とも必要になる。特に有機分子の持つ幾何学的な特徴・機能を活かすことにより、新しいエレクトロニクスの分野が開かれると考えられる。そこで、本解説記事では、有機分子・材料の幾何学的断面に注目し、分子システム、有機プロセス、界面現象制御、デバイス物理という4つの切り口から最近のエレクトロニクス研究の流れと克服すべき課題について概説した。

有機デバイスに関連した研究が活発である。学会での関連分野の研究発表件数の増大は、このことを物語っている。しかし、研究対象とするＦＥＴ，ＥＬなどのデバイスの中で、有機材料本来の機能が活かしきれていないのが実状である。柔軟さなど有機材料独特の機能を使い切るためには、有機分子の幾何学的形状、界面のトポロジー、分子集合体のパターン、分子・分子集合体の動的な挙動など、有機材料の特徴を総合的にとらえ、その扱いを可能にするデバイス物理・工学手法が必要である。「界面幾何工学」という視点からの研究はその糸口となる。そこで本稿では、「界面幾何工学」という視点から、最近の有機エレクトロニクス関連の研究を概観し、その将来展望について述べる。

It is important, both for basic science and device<br /> applications, to investigate the static and dynamic director distribution in a thin nematic liquid crystal (NLC) slab confined between two transparent electrodes. Optical and electrical measurement methods are generally used to determine the director distribution as a function of an electric field. It is to be expected that deuterium NMR spectroscopy combined with simultaneous in situ observation of the light transmittance should give us a good understanding of the director distribution for a thin NLC slab because the former is the sum of the spectra for each position in the slab and the latter by the optical anisotropy averaged over the slab. This combined method is used to investigate the director distribution in a thin<br /> NLC slab of 4-pentyl-40-cyanobiphenyl subject to competing constraints.

本論文は、平成17年9月にノビシビルスク工科大学（ロシア）で<br /> 行った講演発表をまとめ、ロシアの科学論文誌へ寄稿したものである。論文内容は、著者が近年進めている、重水素化核磁気共鳴法を用いた液晶ダイレクタの静的・動的挙動研究の成果概要を述べるとともに、同研究分野での問題点と、それらの解決に向けた理論的・実験的な方向を示した。

Deuterium NMR spectroscopy has been used to investigate the director dynamics in the smectic A phase of perdeuteriated 4-octyl-4 '-cyanobiphenyl-d(25) (8CB-dA(25)), where the director was aligned by an electric field. The electric field direction made an angle of 44.7 degrees with the magnetic field in order to provide a unique alignment pathway; accordingly the director is expected to rotate as a monodomain. When the electric field is applied to the nematic film, the director moves from being parallel to the magnetic field to being at an angle with respect to it. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the turn-on and the tum-off alignment processes as a function of time. This particular technique was chosen because the spectral peaks associated with each rigid group in the molecule are clearly resolved and of comparable intensity. For all of the experiments at different temperatures in the smectic A phase of 8CB-d(25) We found that the relaxation times are independent of the group used to determine the director orientation during the alignment process as same as the results for the nematic phase. It also was found that the relaxation time in the smectic A phase is about 1,000,000 times as large as that in the nematic phase. This results in a strong pretransitional growth of the relaxation time as the transition to the smectic A phase is approached. (c) 2005 Elsevier B.V All rights reserved.

A series of fluoro-substituted alpha,omega-bis-diphenyloxyalkanes have been investigated as possible dopants for nematic liquid crystal display mixtures to reduce the rotational viscosity and hence response times of the mixtures. The compounds have been prepared using the Williamson synthesis, and the effect of the dopants on the mesophase transition temperature of a suitable Merck display mixture host ( ZLI-4792) has been determined. Measurements of magnetic field-induced relaxation times for director reorientation have been made on the doped and undoped mixtures using a novel electron spin resonance ( ESR) method developed by some of the authors. The relationship between field-induced relaxation times and the rotational viscosity is explained and results are reported for the rotational viscosity of the host material. A brief discussion of the molecular theories of rotational viscosity of nematic liquid crystals identifies the important molecular factors as shape, size, flexibility and orientational order parameter. The influence of the dopant molecules on the orientational order parameter of the doped mixtures has been measured using a static ESR method, and these results enable the separate effects of the dopants on the order parameter of the host and on the rotational dynamics to be identified. Results for field-induced relaxation times and order parameters of doped mixtures are reported for seventeen alpha,omega-bis-fluoro-diphenyloxyalkane dopants. Additionally comparative results are reported for a structurally related compound 1,2-trans-di(4'-propylphenyl) 1',2'- difluoroethane. It is found that particular substitution patterns of fluorine atoms in the phenyl rings of the dopant compounds can result in shorter relaxation times for the nematic display mixture investigated. The use of flexible dimers as dopants provides an additional design aid in the development of nematic mixtures for applications.

We have used deuterium NMR spectroscopy to investigate the director dynamics and equilibrium behaviour in nematic liquid crystals (4-pentyl- and 4-octyl-4'-cyanobiphenyl, (5CB and 8CB), both specifically deuteriated) when subject to magnetic and a. c. electric fields. The angle between the magnetic and electric fields can be varied between 0 and 90 degrees and the most common geometry we have used is for an angle of about 45 degrees. For 5CB and 8CB (with positive Delta chi and Delta epsilon) the director orientation was measured using time-resolved NMR both when the electric field is applied and when it is turned off. In all cases it was found that the director alignment was uniform and the director relaxation follows closely the predictions of the torque-balance equation given by the Leslie- Ericksen theory. In all these experiments we have employed a 10 kHz electric field; at such a relatively high frequency the director experiences an effectively constant value of the electric field. We have now investigated the behaviour of the nematic director for the two liquid crystals at much lower frequencies of the electric field: several Hz to about 1000 Hz. As before, the director orientation was measured using time-resolved deuterium NMR spectroscopy. We have employed two geometries. In one, the electric and magnetic fields were inclined at 50 degrees. We found that the director oscillates between two extreme orientations (determined by the frequency and the field strength) in a plane formed by the magnetic and electric fields. The oscillations were observed to continue for many cycles, indicating that the coherence in the director orientation was not lost during this motion. The director was found to remain uniformly aligned. The two extreme director orientations can also be determined from the NMR spectrum time-averaged over many thousands of cycles of oscillations. At low frequencies (several Hz) these limiting angles are essentially independent of frequency but as the frequency increases so the two angles approach each other and become equal at high frequencies. More recently, we have used a geometry with the angle between the fields of similar to 90 degrees. A threshold behaviour is observed in this geometry for the director orientation as a function of the applied voltage. The time-averaged spectra at low frequencies and at certain voltages showed unusual powder-like features. Time-resolved NMR measurements at 40 Hz and different voltages near the threshold value were carried out to understand the oscillatory behaviour which was also simulated. Turn-on and turn-off dynamics at high frequency were conducted revealing intriguing differences between the two pathways for the field-induced relaxation. These results will be discussed and interpreted in terms of the torque-balance equation with a time dependent electric field.

本論文では、外部電場重複印加による重水素化核磁気共鳴法を用<br /> いたネマチック液晶ダイレクタの動的挙動実験により得られる液晶の物理定数の解析法を新たに提案した。この解析法と核磁気共鳴実験の組み合わせにより、液晶の帯磁率異方性、誘電率異方性、測定系における電場と磁場のなす角度を正確に決定できることを示した。

Deuterium NMR spectroscopy has been used to investigate the director dynamics of deuteriated 4-alpha,alpha-d(2)-nonyl-4 '-cyanobiphenyl, where the director was aligned by an electric field. The electric field direction made an angle of 47 degrees with the magnetic field in order to provide a unique alignment pathway; accordingly the director is expected to rotate as a monodomain. The time dependence of the director orientation was investigated at different temperatures. At each temperature in the nematic phase, all of the deuterium NMR spectra indicate that the director was uniformly oriented as a monodomain. It was found that the relaxation time in the smectic A phase is about 1,000,000 times as large as that in the nematic phase. This also results in a strong pretransitional growth of the relaxation time as the transition to the smectic A phase is approached.

We have investigated the oscillatory behavior of the nematic director for 4-pentyl-4'-cyanobiphenyl (5CB) when it is subjected to a static magnetic field and a sinusoidal electric field. In these experiments the two fields were inclined at about 50degrees and the frequency of the electric field was varied from several hertz to approximate to1000 Hz. The director orientation was measured using time-resolved deuterium NMR spectroscopy since this has the advantage of being able to determine the state of director alignment in the sample. In fact, for all of the frequencies studied the director is found to remain uniformly aligned. Since the diamagnetic and dielectric anisotropies are both positive the director oscillates in the plane formed by the two fields. These oscillations were observed to continue for many cycles, indicating that the coherence in the director orientation was not lost during this motion. The maximum and minimum angles made by the director with the magnetic field were determined, as a function of frequency, from the NMR spectrum averaged over many thousand cycles of the oscillations. At low frequencies (several hertz) these limiting angles are essentially independent of frequency but as the frequency increases the two angles approach each other and become equal at high frequencies, typically 1000 Hz. Our results are well explained by a hydrodynamic theory in which the sinusoidal time dependence of the electric field is included in the torque-balance equation. This analysis also shows that, for a range of frequencies between the high and low limits, these NMR experiments can give dynamic as well as static information concerning the nematic phase. (C) 2004 American Institute of Physics.

本論文では、8CB液晶の層構造を有するスメクチックA相でのダイレクタ動的挙動を電界重複印加による重水素化核磁気共鳴法により調べた。磁場と電場が直交する系では、ダイレクタ動的挙動が縮退し、その緩和過程を理解することは困難である。ここでは、磁場と電場のなす角を90度以下に設定することにより、層構造を有する液晶相においても、ダイレクタ回転の緩和過程を明確にできることを示した。

アンカリング強度の周期変化を有する基板を用いたホモジニアス液晶セルは、電場印加により異常な光漏洩現象が発生することを既に報告している。本論文では、この光漏洩現象の発生機構が、一般化表面アンカリング理論と連続体理論に基づき、周期的なアンカリング強度変化 により誘起される表面ダイレクタ歪みに 起因することを明らかにした。さらに、 光配向膜を用いて一次元アンカリング強度周期変化セルにより理論解析結果を実験的に確認した。

The response times of liquid crystal display devices are determined by a range of factors but the most important of these is usually the rotational viscosity coefficient, gamma(1). In order to understand the relationship between molecular structure and viscosity it is of considerable interest to measure this viscosity coefficient for a variety of nematogens. Here we report the determination of gamma(1) for 4-octyl-4'-cyanobiphenyl-d(2) at two temperatures using deuterium NMR spectroscopy. In these experiments the time taken for the alignment of the director can be changed by a field, either magnetic or electric. To do this the liquid crystal film was enclosed in a cell which allows the application of an electric field within the NMR spectrometer. The rate of director relaxation was followed by recording the deuterium NMR spectrum as a function of time during the process of turning the electric field on or off. We have carried out the experiments for a geometry in which the director orientation with respect to the magnetic field of the spectrometer does not exceed 45degrees. The alignment of the director throughout the relaxation process was observed to be uniform. The director relaxation was found to follow closely the predictions of the torque-balance equation given by the Leslie-Eriksen theory. The relaxation times for the turn-on and turn-off processes were determined from this equation and found to be of the order of 1-2 ms. A knowledge of the anisotropic electric and magnetic susceptibilities then allows the determination of the rotational viscosity coefficient.

Deuterium NMR spectroscopy has been used to investigate the director dynamics in the nematic phase of perdeuteriated 4-octyl-4'-cyanobiphenyl-d(25) (8CB-d(25)) When the electric field is applied to the nematic film, the director moves from being parallel to the magnetic field to being at an angle with respect to it. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the, turn-on and the turn-off alignment processes as a function of time. This particular technique was chosen because the spectral peaks associated with each rigid group in the molecule are clearly resolved and of comparable intensity. For all of the experiments at different temperatures in the nematic phase of 8CB-d(25) we find that the field-induced relaxation times are independent of the group used to determine the director orientation during the alignment process.

Deuterium NMR spectroscopy together with spectral simulations have been used to investigate the field-induced director dynamics in a nematic liquid crystal, 4-pentyl-4&apos;-cyanobiphenyl (5CB), conned in a slab between two electrodes. The NMR spectra have been measured when turning the electric field on and turning it off. Measurements were also made at different temperatures to explore how the temperature effects the director relaxation. At higher temperatures, some complications arise as peculiar oscillations are observed in the spectra. With spectral simulation this phenomena is shown to result from the relaxation of the director on a timescale comparable to that of the experiment which is the effective spin-spin relaxation time. The simulated spectra are compared with the experimental spectra for the specifically deuteriated 5CB-d(2).

We have investigated the voltage dependence of the light transmittance for homogeneous thin nematic liquid crystal (NLC) cells composed of 4-pentyl-4'-cyanobiphenyl (5CB), which were confined between two glass plates. The substrate surfaces with polyimide layers were rubbed unidirectionally to make a uniform planar director orientation with a strong surface anchoring condition. An NLC cell was set between polarizer and analyzer. The He-Ne laser beam was passed through the NLC slab oriented with its optic axis parallel to the linearly polarized direction of the light beam. The light transmitted through the analyzer, which was crossed with the polarizer, was detected as a function of the applied voltage. In zero electric field it is expected that the director will have a uniform planar alignment and this orientation gives a minimum intensity of the light transmitted. When the voltage is applied to the NLC cell, the director for 5CB with its positive dielectric anisotropy rotates to orient parallel to the electric field. The voltage dependence of the light transmittance showed an anomalous result; that is, light leakage was observed for a certain voltage. This was interpreted by considering the director deformation at the boundaries between rubbed and non-rubbed regions of the polyimide surface.

Deuterium nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the director dynamics in the nematic liquid crystal, 4-pentyl-4'-cyanobiphenyl (5CB), confined between two glass plates and subject to magnetic and electric fields. The nematic cell was held in the NMR probe head so that the electric field, whose direction is normal to the substrate surface, makes an angle of about 45degrees with the magnetic field. This experimental geometry avoids the degeneracy in the field-induced alignment pathway for the director found for larger angles. A series of deuterium NMR spectra, obtained using a quadrupolar echo sequence, was acquired as a function of time. When the electric field, whose intensity is controlled so that the director makes an angle with the magnetic field is applied to the nematic film, the director moves from being parallel to the magnetic field to being at an angle with respect to the magnetic field because Delta(&epsilon;) over tilde and Delta(&chi;) over tilde are both positive for 5CB. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the turn-on and the turn-off alignment processes as a function of time. The realignment pathway of the director was monitored by measuring Delta(&nu;) over tilde, the deuterium quadrupolar splitting. We have studied the time dependence of the director orientation for the turn-on and turn-off processes at different temperatures in the nematic phase. The temperature independence of Delta(&chi;) over tilde/Delta(&epsilon;) over tilde is also discussed on the basis of experiment and theory. The diamagnetic anisotropy and the rotational viscosity coefficient were also determined as a function of temperature. The deuterium NMR spectra corresponding to the field-induced director dynamics were predicted by an analysis based on hydrodynamic theory. (C) 2002 American Institute of Physics.

Studies of the field-induced alignment of the nematic <br /> director for low molar mass materials using vibrational spectroscopy have revealed some fascinatingly unexpected results. Several studies have found that the relaxation time for the director alignment is dependent on the group in the molecule used to monitor the director orientation. Seemingly this undermines the basic concept of the Leslie-Ericksen hydrodynamic theory of nematics. Here we report <br /> complementary studies using deuterium NMR spectroscopy of <br /> perdeuteriated 4-pentyl-4￠-cyanobiphenyl where the director is aligned by a magnetic or an electric field. This particular technique was chosen because the spectral peaks associated with each rigid group in the molecule <br /> are clearly resolved and of comparable intensity. We have investigated the director alignment using different temperatures, electric field strengths and angles between the magnetic and electric fields, each of which influences the director relaxation time. For all of the experiments we find that the relaxation times are independent of the group used to determine the director orientation during the alignment process.

Macroscopically, the surface-induced director orientation has an influence on that in the bulk．It is important for basic science and device applications to investigate the director distribution in a thin nematic slab experimentally and theoretically．In this study the director deformation in nematic slabs with different surface anchoring conditions has been investigated using a deuterium nuclear magnetic resonance spectroscopy method．A series of NMR spectra has been acquired as a function of the applied electric field normal to the magnetic field, which can also be used to provide an estimate of the director deformation．This experimental techniques help to give us a better understanding of the surface-induced static director distribution．

We have studied the static director distribution in thin nematic liquid crystal cells with different film thicknesses and different surface anchoring strengths using a combination of deuterium nuclear magnetic resonance (NMR) spectroscopy and continuum theory. A nematic liquid crystal, 4-pentyl-d(2)-4'-cyanobiphenyl (5CB-d(2)) deuteriated in the ct position of:the pentyl chain, was confined between two glass plates with both weak and strong anchoring conditions; the anchoring strengths were measured by using a saturation voltage method. A series of deuterium NMR spectra, obtained using a quadrupolar echo sequence, was acquired as a function of the applied electric field, which can be used to explore the:director deformation. The deuterium NMR spectra predicted by continuum theory involving the magnetic, electric, elastic, and unified surface anchoring energies are found to be in good agreement with experiment. The investigation also reveals that profiles of the director distribution for the case with a magnetic field have a top-hat shape different to the bowler-hat shape, which is well known as the director profile for the case with no magnetic field. (C) 2001 American Institute of Physics.

Deuterium NMR spectroscopy has been used to investigate the director dynamics in the nematic liquid crystal, 4-pentyl-4&#039;-cyanobiphenyl, confined between two glass plates and subject to the magnetic and pulsed electric fields. A series of deuterium NMR spectra, obtained using a quadrupolar echo sequence, was acquired as a function of the applied electric field and time. When the electric field, whose intensity is controlled so that the director makes an angle with the magnetic field is applied to the nematic film, the director moves from being parallel to the magnetic field to being <br /> at an angle with respect to the magnetic field because of a <br /> positive and for 5CB. After the electric field is switched off, the <br /> director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the turn-on and the turn-off realignment processes as a function of time. The realignment pathway of the director <br /> was monitored by measuring i, the deuterium quadrupolar splittings. We <br /> have studied the time dependence of the director orientations for the turn-on and turn-off processes. The deuterium NMR spectra corresponding to the

Deuterium NMR spectroscopy has been used to investigate the director dynamics in the nematic liquid crystal, 4-pentyl-4&#039;-cyanobiphenyl, confined between two glass plates and subject to orthogonal magnetic and pulsed electric fields. When the pulsed electric field, whose intensity is strong enough to make the director align normal to the magnetic field, is applied to the nematic film, the director moves from being parallel to the magnetic field to being parallel to the electric field. After the pulsed electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the turn-off realignment process as a function of time. With this experimental geometry the director alignment is not unique as it can rotate equally probably clockwise or counterclockwise in this realignment process. That is, the realignment pathway for the director is degenerate, which establishes a director flow pattern. We have studied the time dependence of the director orientation and distribution for the turn-off process. The deuterium NMR spectra corresponding to the director dynamics in the realignment pathways were predicted

先に報告した一般化表面アンカリングエネルギモデルより飽和閾値法が導かれる。本手法を用いて、種々の配向膜に対するシアノ系液晶およびフッソ系液晶の表面アンカリングエネルギを測定した。表面アンカリングエネルギ増加に対するチルト角の変化は、シアノ系およびフッソ系液晶では逆の傾向を示す。配向膜材料については、膜表面での電子密度と同等以上に、配向膜分子側鎖による液晶分子挙動の阻害が表面アンカリングエネルギに影響を与える。

The director distribution in a thin nematic liquid crystal (NLC), 4-pentyl-d2-4&#039;-cyanobiphenyl (5CB-d2) deuteriated in the a-position of the pentyl chain, confined between two glass plates, with untreated and treated anchoring conditions, has been investigated using a deuterium nuclear magnetic resonance (NMR).<br /> The NMR spectra have been measured as a function of the applied electric field.In the absence of surface forces it is found that the director aligns parallel to the magnetic field at relatively low values of the electric <br /> field as the dielectric anisotropy is positive for 5CB. Then as the electric field is increased the director remains parallel to the magnetic field until some critical value of the electric field, at which point the director is aligned parallel to the electric field and <br /> hence perpendicular to the magnetic field, since the diamagnetic anisotropy is positive for 5CB. In the presence of surface forces with increasing electric field the quadrupolar splitting decreases, passes through zero and then increases again to a value which is essentially half of that at zero electric field. That is, the director orientation changes more or

Deuterium nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the electric field-induced alignment of the director of the smectic A phase of the liquid crystal, 4-α,α-d2-octyl-4&#039;-cyanobiphenyl (8CB-d2), at 303.3K. The electric field is arranged to be orthogonal to the magnetic field.<br /> The alignment process has been investigated at different electric field strengths and the rate of director alignment was monitored by recording the deuterium NMR spectra as a function of time after the electric field was switched on.The results reveal a complex pattern of electric field-induced director alignment. At high electric field strengths a rapid process is observed in which the director switches from an orientation parallel to the magnetic field to one in which it is parallel to the electric field. An induction period is also observed in which no apparent change in director orientation occurs. This induction period becomes longer (hours in magnitude) as the electric field strength is lowered. <br /> Other, intermediate, director orientations are observed as the electric field strength is lowered further. The role of defects is invoked in trying to interpret some of

The director distribution in thin nematic slabs with allel <br /> structure have been calculated as a function the applied electric field. They are different from the cells with the anti-parallel structure, in that three solutions exist in a specified voltage range which predict a transition of the director deformation from splay to bend onfigurations in the parallel structure.This splay-bend transition has been confirmed experimentally by a capacitance-voltage (C-V)hysteresis method. The C-V characteristics showed a esis around the deformation transition and this magnitude corresponded to the facility of the splay-bend transition:<br /> a comparison of these hysteresis characteristics for different materials enables us to evaluate the splay-bend transition speed easily.

Deuterium nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the field-induced director dynamics in a nematic liquid crystal,4-pentyl-d2-4&#039;-cyanobiphenyl (5CB-d2) deuteriated in the a-position of the pentyl chain, confined between two glass plates. The NMR spectra have been measured as a function of time after turning an electric field on and off.It is demonstrated that the field-induced director dynamics in the nematic liquid crystal cells can be successfully<br /> time-resolved. In addition, it is found that the doublet <br /> NMR spectra become powder-like during the turn-on and turn-off processes. It is shown that the rotational viscosity and the diamagnetic anisotropy of 5CB-d2 can be determined <br /> from the time-resolved NMR spectra by assuming uniform alignment of the director.

Transient diffraction phenomena induced by external applied electric field to nematic liquid crystal cells have been investigated. Far-field ring diffraction pattern is observed and is caused by a quasiperiodic herringbone pattern. It is found that the electric-field and the temperature dependences of the diffraction transients have <br /> correlation with those of current transients due to the conduction of impurity ions. It is concluded that the transient diffraction is attributable to the ion conduction via the formation of the herringbone texture.

The unified surface anchoring energy was investigated for <br /> nematic slabs of various cyano- and fluorinated liquid crystals on a polyimide alignment layer. The surface anchoring strength was found to vary over the range 10^-4 to 10^-3 J/m^2 dependent on the liquid crystal structure. It was also found that the values of surface anchoring strength change with respect to the tilt angle in opposite <br /> directions for the cyano- and fluorinated liquid crystals.