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We developed a compact microfluidic measurement system based on a filter-free fluorescence sensor that can selectively identify wavelengths without optical component. Two types of fluorescent beads were successfully identified using this proposed system. The sensor detects the wavelength and intensity of light using a potential peak inside formed by the photogate (PG) voltage. The conventional method detects only electrons moving toward the PG side, but we also focused on electrons moving toward the n-well side of the sensor. Using this current, the wavelength is identified from the ratio of the two currents (I n-well /I PG ). In the past, at least two measurements were required, but with this method, identification can be realized in a single measurement. These results are expected to be applied to the field of cell measurement.

We report the world-first result of visualization of intra-stem ion dynamics of living plants using a novel ion image sensor. A dedicated ion image sensor that can insert to the plant stem was fabricated. The sensor has $128\times 32$ ion-sensitive pixels to capture the ion distribution reflecting the structure of the stem (vascular bundle). Imaging results showed that hydrogen ions moved from the bottom to the top of the stem due to natural transpiration. Ion distribution reflecting the vascular bundle was also clearly visualized and confirmed to correspond with the plant stem cross-sectional structure. This sensor can be used to observe the activity of photosynthesis and possibly maximize production efficiency in agriculture.

We developed a $256\times 32$ -pixel needle-type pH image sensor to visualize ion behavior at the cellular level under in vivo conditions. This sensor has a pixel configuration that can be fabricated via a modified CMOS process technology, and it achieved a pixel size of $5.65\times 4.39\ \mu \mathrm{m}^{2}$ . The proposed image sensor is the highest-definition implantable ion image sensor among other conventional image sensors. For in vivo implantation, the sensor's shape was modified to a needle structure of $9.88\times 1.10\ \text{mm}^{2}$ with a thickness of $100\ \mu \mathrm{m}$ . From the measurement results, we verified that the sensor exhibits a high spatiotemporal resolution with a pH sensitivity, pH resolution, and temporal resolution of 56.4 mV/pH, 0.015 pH, and 14.1 fps, respectively. In addition, we detected pH changes in the brain of the experimented mouse during neural hyperexcitation, and successfully reproduced the measured data as 2-D images in real time.

Various biosensing platforms for real-time monitoring and mapping of chemical signals in neural networks have been developed based on CMOS process technology. Despite their achievements, however, there remains a demand for an advanced method that can offer detailed insights into cellular functions with higher spatiotemporal resolution. Here, we present a pH image sensor that employs a high-density array of 256 × 256 pixels and readout circuitry designed for fast operation. The sensor's characteristics, such as the pH sensitivity of 55.1 mV/pH and higher frame speed of 1933 fps, are experimentally demonstrated and compared to those of state-of-the-art pH image sensors. Among them, our sensor presents the smallest pitch of 2 μm with a significantly high operation speed. This sensor can successfully detect a pH change, but also transform the measured data to a two-dimensional image series in real time. The practical spatial resolution of images is investigated by an evaluation method that we first propose in this paper. By this method, we confirm that our sensor can discriminate objects distanced over 4 μm apart, which is twice bigger than the pixel pitch. In order to analyze the degraded resolution and image blur, a capacitive coupling effect at an ion-sensitive membrane is suggested as the main factor and demonstrated by simulation.

This study aimed to report a compact microfluidic measurement system, based on a filter-free multiple-wavelength sensor, that can selectively identify wavelengths without using an optical component. Two types of fluorescent beads were successfully identified in the study using the proposed system. The sensor detected both wavelength and intensity of light using a potential peak formed by the photogate (PG) voltage. While conventional method detected only electrons moving toward the PG side and have to modulate the VPG for wavelength measurement, our novel system focused on electrons moving toward the n-well side of the sensor as well. The wavelength was identified from the ratio of two currents, namely In-well and IPG. Furthermore, wavelengths with different absorption characteristics could be identified based on the depth of the potential peak. The findings from this study may eventually be applied in the field of biology, including the quantitative and qualitative analyses of cells.

In Pickering-Ramsden emulsions, the packing structure of the colloidal particles at the liquid-liquid (or liquid-gas) interface significantly affects the structure and behavior of the emulsion. Here, using a series of platelike particles with regular polygonal shapes and Janus amphiphilicity, we created emulsion droplets stabilized by close-packed polygonal particles at the interface. The systematic variation of the particle morphology shows that the geometrical features of the regular polygons in (curved) planar packing dominate over the self-assembled structures. The structures are tessellations of triangular, square, and hexagonal particles at the surface for large droplets and regular tetrahedral, cubic, and dodecahedral particle shells of triangular, square, and pentagonal particles for small droplets, respectively. This work creates the possibility of geometrically designing the structure and functionality of emulsions.

In vivo neural imaging devices are developed not only to record chronically but also to obtain the spatiotemporal information of neurochemical signals. Here, we present an image sensor consisting of a 256 × 256 pixel array and an integrated readout circuitry for a biomedical implantation application. The key idea of this sensor is that a higher resolution array than that of our previous insertable sensor realizes by employing two transistors in our pixel circuit. The proposed sensor architecture was fabricated by a modified 1P4M 0.15 µm CMOS process. This sensor was able to detect a hydrogen ion distribution change during the inserting test carried out at a brain-like object, and to reproduce the measured data into a two-dimensional (2D) image series in real-time.

In this study, we designed and evaluated a new extended gate pH image sensor with accumulation function circuits as a state-of-the-art bio-image sensor. The accumulation function circuit can be expected to amplify the signal by repeatedly transferring the signal charge from the pixel to the capacitor, and to improve the pH resolution from the viewpoint of the signal to noise ratio (SNR). From the measurement results, this image sensor achieved a pH sensitivity of 210 mV / pH and a pH resolution of 0.0099 pH at a single pixel and four times of accumulation. These results indicate the future realization of an image sensor capable of imaging the activity of biological cells with pH resolution of 0.01 pH.

Recently there has been a growing trend toward the development of touch sensing devices with a high spatial resolution in robotic field. Most of all sensors are limited due to their large device size. We have been aimed to develop a high-density and high-resolution pressure sensor array using complementary metal oxide semiconductor (CMOS) imaging technologies. To realize the pressure sensing device, we here propose a bonding technique that connects a polarized film to a 256 × 256 potentiometric sensor array and demonstrate the fabricated device.

We have developed a novel ion image sensor with a fine pixel pitch, which is shorter than one-tenth of the 23.55 μm in the previous design. In this report, we highlight the imaging potential of a 2-μm-pitch ion image sensor in the measurement of the neural activity of mouse hippocampus. This pitch is sufficiently small to observe the action of a single cell. The results of brain-slice imaging indicated that the diffusion of H+ ions was different in each region containing CA1, CA2, and DG in the hippocampus. In addition, the sensor clearly captured the distribution of neural cell responses.

Micrometer-sized colloidal particles dispersed in nematic liquid crystals interact with each other through anisotropic interactions induced by orientational deformation of the nematic field. In the case of so-called dipole nematic colloids, their interaction is of the dipole-dipole type. Two-dimensional, non-close-packed colloidal assemblies having various characteristics were fabricated using optical tweezers by exploiting the attraction between anti-parallel dipole nematic colloids in homeotropically aligned nematic cells. Structures comprising polygons, squares, and tetrahedra were built using equal-sized particles, and hexagonal structures were built using particles of two sizes. As the nematic field is sensitive to electric fields, the response of the fabricated assemblies toward an alternating electric field was also studied. All assemblies exhibited homogeneous reversible shrinkage, and their shrinkage rates were dependent on the structure. The maximum shrinkage rate in the linear dimension of the assemblies was over 20% at 5 Vrms for a hexagon comprising tetrahedral units.

The self-propelled motions of micron-sized nematic liquid crystal droplets in an aqueous surfactant solution have been studied by tracking individual droplets over long time periods. Switching between self-propelled modes is observed as the droplet size decreases at a nearly constant dissolution rate: from random to helical and then straight motion. The velocity of the droplet decreases with its size for straight and helical motions but is independent of size for random motion. The switching between helical and straight motions is found to be governed by the self-propelled velocity, and is confirmed by experiments at various surfactant concentrations. The helical motion appears along with a shifting of a point defect from the self-propelled direction of the droplet. The critical velocity for this shift of the defect position is found to be related with the Ericksen number, which is defined by the ratio of the viscous and elastic stresses. In a thin cell whose thickness is smaller than that of the initial droplet size, the droplets show more complex trajectories, including "figure-8s" and zigzags. The appearance of those characteristic motions is attributed to autochemotaxis of the droplet.

In this study, we developed a filter-free fluorescence image sensor that performed 2D fluorescence imaging without optical filters utilizing the wavelength-dependent absorption depth of a silicon substrate. This sensor changes the potential distribution in the depth direction of the silicon substrate by controlling a potential of the polysilicon gate atop the sensing area. And it can display both images of excitation light and fluorescence at the same time by measuring each light absorption current. We obtained a 2D image of quantum dot emission immobilized on the 32 χ 32 filter-free fluorescence image sensor. Quantum dot emitted light with a wavelength of 620 nm by excitation light with a wavelength of 470nm. The proposed image sensor can measure and display 2D images of more than two kinds of light wavelengths at the same time by controlling the photogate voltage.

We studied the opto-mechanical response of droplets composed of cholesteric liquid crystal (ChLC) to a circularly polarized optical tweezers. Although the alignment of LC molecular within a droplet depends on the relative ratio of the droplet diameter d to the helical pitch p, the optically induced rotation was found to be asymmetric to the direction of circularly polarized light irrespective to the inner molecular alignment. We studied the rotation of the droplets with various sizes, helical pitch (strength of chirality) and different chirality. In the case of d/p ~ 1, the direction of the rotation was simply determined by chirality of ChLC and the rotation was also observed for linearly polarized light, which has already been reported by Yang et al.

A patchy colloidal particle possesses distinctive regions with different physical or chemical properties on its surface and thus exhibits anisotropic interactions with another particle or object. By utilizing the large van der Waals attraction between metal surfaces and the electric double layer repulsion originating from surface charge, we succeeded in controlling the adsorption behavior of metallodielectric particles (MDPs), which were composed of dielectric spheres each with a thin gold patch modified with dissociable groups, to gold surfaces. When MDPs were dispersed on a dielectric substrate with a thick gold pattern in aqueous solution, the particles selectively adsorbed onto the gold surface of the substrate at a moderate salt concentration. Furthermore, when MDPs were mixed with large particles coated with a thick gold film, MDPs adsorbed on the gold surface at a moderate salt concentration and formed a monolayer. In the monolayer, gold patches of MDPs bonded to the gold surface and the dielectric surface of MDPs faced outward. In other words, this monolayer was a solid dielectric layer formed on the metal surface of a large particle. Such selectivity, i.e., that a gold patch of an MDP bonded to a gold surface but the patches did not bond to each other, was realized by controlling the thickness and surface charge of gold patches.

Electrophoretic mobility has been widely used to evaluate the zeta potential of individual colloidal particles, which governs the stability of colloidal dispersions. We demonstrated two experimental methods to measure the AC electrophoretic mobility μ of micron-sized single particles using holographic video microscopy. The three-dimensional position of the particle was estimated by reconstructing the light field from its two-dimensional holographic image, using the Rayleigh-Sommerfeld back-propagation method. In a planar electric field setup, the height dependence of the measured value of μ in the cell enables us to evaluate the actual value of μ, without interference from electroosmotic flow. In a vertical setup, the true value of μ can be directly evaluated by minimizing the influence of the electrode polarization, using a thick cell and a high-frequency electric field. The estimated values of μ obtained using both methods agree with that from conventional electrophoretic light scattering. We also evaluated the distribution of μ values within a colloidal dispersion.

In this paper, the detection of fluorescence from the solution of a fluorescent dye with a submicromolar concentration by the filter-free fluorescence sensor is reported. The filter-free fluorescence sensor has a photo-gate structure and the intensities of excitation and fluorescent lights can be calculated from the photocurrents for different gate voltages. It makes it possible to measure various wavelengths even without optical filters and mirrors. The separation ability of excitation light (470 nm) and fluorescence (530 nm) in the developed filter-free fluorescence sensor was 1200:1 for LED light source. The fluorescent measurements were carried out for the dye of fluorescein isothiocyanate isomer. The excitation light with the wavelength of 470 nm was used, and the photocurrents were measured for the gate voltages of 1 V and 3 V, respectively. Based on the calculation, the fluorescence from fluorescein isothiocyanate isomer was detected for the solution with the concentration of as low as 100 nM (12 bases).

Orientational order in condensed matter plays a key role in determining material properties such as ferromagnetism, viscoelasticity or birefringence. We studied purely orientational ordering in closely-packed one-patch colloidal particles confined between flat substrates, where the particles can only rotate and are ordered via the sticky interaction between the patches. For the first time, we experimentally realized a rich variety of mesoscopic patterns through orientational ordering of colloids by controlling patch size and confinement thickness. The combination of experiment and numerical simulation reveals the decisive role of confinement: An ordered state(s) is selected from the (meta)stable options in bulk when it is commensurate with the system geometry and boundary conditions; otherwise, frustration induces a unique order. Our study offers a new means of systematic control over mesoscopic structures via orientational ordering in patchy particles. The system would also possess unique functionalities through the rotational response of the particles to external stimuli.

Microorifice-based fusion makes use of electric field constriction to assure high-yield one-to-one fusion of selected cell pairs. The aim of this paper is to verify feasibility of high-yield cell fusion on a microfluidic chip. This paper also examines viability of the fusant created on the chip. We fabricated a microfluidic chip to fuse selected cell pairs and to study postfusion behavior. We used a self-forming meniscus-based fabrication process to create microorifice with a diameter of 2-10 microm on the vertical walls in a microfluidic channel. When 1 MHz was applied to electrodes located on both sides of the microorifice, dielectrophoretic force attracted the cells toward microorifice to form a cell pair. Once the cells get into contact, fusion pulse was applied. Real time imaging of cells during fusion and cytoplasmic dye transfer between cells indicated success of cell fusion. We found that when high frequency voltage for dielectrophoresis was swept from 1 MHz to 10 kHz in 100 micros, cell fusion was initiated. The effective electric field strength was 0.1-0.2 kV/cm. We analyzed viability by imaging fusant going into cell division phase after 48 h of incubation. We conclude that fabricated microfluidic chip is suitable for high-yield one-to-one fusion and creation of viable fusants. This technology should be a useful tool to study fusion phenomena and viability of fusants, as it allows imaging of the cells during and after the fusion.

Interparticle force F between two colloidal particles accompanied by hyperbolic hedgehog defects has been studied in nematic liquid crystal by two methods. We have directly measured F as a function of interparticle distance R in the case of two “dipoles” composed of a particle and an accompanied defect aligning parallel to the far-field director. We have confirmed the theoretical prediction that F is proportional to R−4 at longer distance but the magnitude of F is different in two methods. We have also observed that repulsive component emerges at shorter distance.

We studied Isotropic-Nematic (I-N) phase transition by nonlinear dielectric measurement. The third-order nonlinear permittivity ϵ3 was obtained from the third harmonic component of the electric displacement under AC electric field. The obtained ϵ3 shows the critical behavior in I phase near I-N transition point with the critical component of one. This result agrees well with the critical behavior predicted by mean − field theory, but that of the relaxation time deviates from the theoretical prediction.

We apply nonlinear dielectric spectroscopy to an antiferroelectric liquid crystal MHPOBC at various smectic sub-phases. In the SmCα* phase, the third-order nonlinear dielectric spectrum ϵ3* is found to be composed of the contributions from ferroelectric soft mode and soft mode of the SmCα* phase. The obtained spectrum is well ascribable by the theoretical one calculated by the Landau-type of phenomenological theory. In the SmC* phase, ϵ3* shows a complicated form, and is different from one observed in usual ferroelectric liquid crystals. In the SmCFI1*( SmCγ*) phase, ferrielectric Goldstone mode with broad distribution of relaxation times is observed in both ϵ1* and ϵ3*.

Dynamics of nano-sized colloidal particles in a swollen lyotropic lamellar phase ofa nonionic surfactant has been studied by three methods of microrheology. By electrophoreticmicrorheology (EPM), we find two relaxation processes respectivelyrelating to the fluctuation of membranes and topological defects in lamellarstructure. By direct tracking of particles under a microscope and manipulatingthem with an optical tweezers, we obtained detailed information on diffusion ofa particle at low frequencies. We observed the jump-trap motion of a particleand the non-Newtonian rheological behavior at low frequencies.

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ions —mass and charge state— was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X2Π-A2Σ+ transition of nitric oxide (NO) molecules. A mass resolution m/Δm ≥180±6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO+ ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T.

Fiber-shaped H-aggregates with lengths of up to 300 microm are synthesized by self-assembly of thiacyanine (TC) dye molecules in solution. Photoluminescence (PL) images and spatially resolved PL spectra of the fibers that are transferred onto a glass substrate reveal that the fibers act as single-mode optical waveguides that propagate PL in the range of 520 to 560 nm over 250 microm without any loss.

Nonlinear dielectric spectroscopy in frequency domain has been applied to antiferroelectric liquid crystals in various smectic phases including antiferroelectric SmC A *, SmC FI2 * and incommensurate SmCα* phases. We have observed different characteristic third-order nonlinear dielectric spectra ϵη3* in respective phases. In SmC A * and SmC FI2 * phases, nonlinear dielectric response originated from Goldstone-like fluctuation with long relaxation time along the helical structure have been observed, which cannot be usually observed in linear spectrum. In the SmCα* phases, we have observed the critical behavior of soft mode that condenses in the SmCα* phase by ϵ3*. The obtained nonlinear dielectric spectra are discussed by using phenomenological models for respective relaxation.

We developed a low-detection-limit filter-free fluorescence sensor by a charge accumulation technique. For charge accumulation, a floating diffusion amplifier (FDA), which included a floating diffusion capacitor, a transfer gate, and a source follower circuit, was used. To integrate CMOS circuits with the filter-free fluorescence sensor, we adopted a triple-well process to isolate transistors from the sensor on a single chip. We detected 0.1 nW fluorescence under the illumination of excitation light by 1.5 ms accumulation, which was one order of magnitude greater than that of a previous current detection sensor.

Micro-sized colloidal particles dispersed in nematic liquid crystal become topological defects in uniform orientation of liquid crystal. Since they increase the elastic energy of the liquid crystal, a long-ranged anisotropic interaction is induced between them. In this study, we reported the interparticle force measured by various methods utilizing optical tweezers. The interparticle force depends on the type of particle-defect pair and its dependence on the interparticle distance is in agreement with the theoretical prediction using electrostatic analogy. This anisotropic force enables us to construct characteristic clusters, which cannot be realized in conventional water-based colloidal dispersions. We made some novel colloidal assemblies in two dimensions by utilizing optical tweezers to demonstrate the availability of the anisotropic force in nematic colloids

A developmental project has been initiated to create a new type of glass fabric, whose fibers are to be uniformly distributed in the laminate so as to comply with the requirement of homogeneity. As a result, various types of glass fiber fabrics have successfully woven through the uniquely developed “MS process”, and it has been verified that each of the glass fabrics possesses the most suitable structure to attain uniform distribution in the laminates. The laminates, using the newly developed glass fabrics, have proved that the micro‐diameter drilling, that is laser drilling and mechanical drilling with 0.1mm diameter, can be performed very easily with less drill bit breakage, and produces uniform drill holes. It has also been proved that the laminates with the new glass fabrics reveal improved mechanical properties such as lower CTE, decreased warp and twist and better dimensional stability compared with conventional laminates of glass epoxy. Various styles of new glass fabric cover the wide range of thickness from 100 microns down to 27 microns.

We developed a new method for measuring the dynamic electrophoretic mobility μ* and apparent diffusion coefficient D of colloidal particles in a sinusoidal electric field by employing the heterodyne method of light scattering. The frequency of the scattered light is sinusoidally modulated due to the Doppler effect if there is no Brownian motion of colloidal particles. The undesirable influence of Brownian motion is removed by squaring the time-domain signal, and μ* is obtained from the second and fourth harmonic components of signal detected with a lock-in amplifier. On the other hand, the influence of electrophoresis is excluded to obtain D by calculating the autocorrelation function of the component at the same frequency of the applied electric field. This method is applied to a suspension of latex particles, and the complex spectrum of μ* is successfully measured for the first time in a wide frequency range below 50 kHz. The obtained spectrum of μ* shows relaxation, and the apparent diffusion coefficie...

The nonlinear dielectric relaxation spectra of ferroelectric liquid crystals (FLCs) have been studied in the chiral smectic-C phase. The linear and third-order nonlinear dielectric spectra show the relaxation corresponding to the fluctuation in the azimuthal angle of directors called the Goldstone mode. We calculated the nonlinear dielectric spectra of the Goldstone mode theoretically by the torque balance equation which describes the dynamics of FLCs under the electric field. The calculated spectra make good agreement with the measured ones. We also evaluated the material constants of FLCs from the best-fitted values of the linear and nonlinear dielectric increment and relaxation time.

We have applied a nonlinear dielectric relaxation spectroscopy to the Goldstone mode of ferroelectric liquid crystals (FLCs) in the chiral smectic C phase. The linear spectrum shows a single relaxation of Debye type. The third and fifth-order nonlinear spectra show extended forms of Debye type to the nonlinear cases. We have also calculated the nonlinear dielectric spectra theoretically by means of the torque balance equation describing the dynamics of FLCs. The theoretical spectra in which we have taken into the distribution of the relaxation times make good agreement with the measured ones. We also discuss the application of nonlinear dielectric relaxation spectroscopy to the simultaneous measurement of material constants of FLCs.

Frequency domain electric birefringence spectroscopy has been applied to a typical soluble conducting polymer, poly(3-hexylthiophene), in dilute solutions in order to investigate the isolated single-chain dynamics of conducting polymers. From the results, the intramolecular conduction mechanism in a single conducting polymer chain is revealed without interference from the inter-chain one. The change in hydrodynamic diameter of the polymer chain with varying temperature or solvent species clearly indicates the occurrence of a single-chain conformational transition. Further, it turns out that there exist two kinds of carrier transport process along the polymer chain with different diffusion distances and diffusion constants, which reflect a disorder effect due to conformational defects on the one-dimensional polymer chain.

We have studied the nonlinear electrooptical relaxation spectra of the Goldstone mode in a ferroelectric liquid crystal (FLC). The linear spectrum experimentally obtained shows a single relaxation of Debye type and the second and third-order nonlinear spectra show an extended form of Debye type to a nonlinear case. We have also studied the electrooptical response theoretically by means of a simple torque balance equation describing the dynamics of the Goldstone mode. The calculated nonlinear spectra are found to be in a rather good agreement with experimentally obtained ones.

We measured the fluctuations of a lyotropic liquid crystal lamellar (Lα) phase in dilute surfactant concentration and a sponge (L3) phase by dynamic light scattering technique. We observed the concentration fluctuation induced by the thermal undulation of layers in the Lα phase and obtained the dependence of the effective rigidity kc of layers on the repeat distance d, which reflected the fluctuation-induced layer softening. In the L3 phase, two kinds of fluctuation modes were observed.

The linear and third-order nonlinear dielectric constants of the antiferroelectric liquid crystal 4-(1-trifluoromethyl-pheptyloxycarbonyl) phenyl ${4}^{\ensuremath{'}}$-octyloxybiphenyl-4-carboxylate were experimentally studied in its smectic-A (Sm-A) and smectic-${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ (Sm-${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$) phases. Both dielectric constants showed a critical behavior near the Sm-A--Sm-${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ phase transition corresponding to the softening of ferroelectric soft mode and the increase of the fluctuation in the tilt direction. In the Sm-${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ phase, no relaxation was observed in the linear spectrum, but the third-order nonlinear dielectric spectrum showed a Debye-type relaxation with a relaxation frequency of a few kHz corresponding to the Goldstone mode in the Sm-${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ phase. This nonlinear response was theoretically analyzed and ascribed to a field-induced biaxiality, i.e., the deformation of the helical structure due to a coupling between the dielectric anisotropy and the electric field. The temperature dependence of the nonlinear spectrum was also discussed. \textcopyright{} 1996 The American Physical Society.

The SmA, SmCα* and SmC* phases of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl) phenyl 4‘-octyloxybiphenyl-4-carboxylate (MHPOBC) have been studied by means of simultaneous meas...

The critical behaviors of the linear and higher-order nonlinear dielectric constants of ferroelectric liquid crystals (FLCs) are studied in the SmA phase near the SmA-SmC* phase transition. The critical exponents of the linear, third-order and fifth-order dielectric constants experimentally obtained are 1, 4 and 7, respectively. These exponents and the signs of nonlinear dielectric constants are in good agreement with those calculated theoretically from the phenomenological theory of Landau type. The influence of the order of phase transition (first or second) on the critical behavior of FLCs is also studied.

The improvement of a filter-less fluorescence sensor, by suppressing forward scattering in silicon by surface planarization is presented. A fluorescence microscope has been widely used in biochemical fields. However, it is difficult to miniaturize because optical filters and other parts are necessary. We previously developed a filter-less fluorescence sensor. The separation ability of excitation light and fluorescence in the previous device was 550:1. It is necessary to improve the separation ability. This study focuses on the suppression of forward-scattered incident light in silicon, through the enhanced surface planarization of polysilicon, which is the gate electrode material. The separation ability of the filter-less fluorescence sensor was increased from 550:1 to 1250:1 by the suppression of forward-scattered light.

Colloidal particles with a limited number of interactive sites are called colloidal molecules, and their assemblies have been intensively studied to reveal complex micro-structures. In this study, we examine colloidal particles in nematic liquid crystals, so-called nematic colloids, as colloidal molecules and fabricated some non-close-packed assemblies. Micrometer-sized particles with homeotropic surface anchoring of liquid crystal in a homeotropic cell interact with each other through dipolar-type anisotropic interactions arising from the elastic deformation of the nematic field around the particles. Using optical tweezers, we have built two-dimensional colloidal assemblies with low packing densities, including polygon-rings, chains of polygon-rings, and lattices composed of octagon-rings in a hierarchical way from smaller structure units. Because the nematic field is sensitive to the electric field, the response of the polygon-rings to an alternative electric field has been studied. They exhibited homogeneous reversible shrink as large as 15%–22% to their original sizes under several volts.

The single-chain dynamics of a typical soluble conducting polymer, poly(3-hexylthiophene), has been studied in solutions by frequency-domain electric birefringence spectroscopy. From the results, we have obtained information on the intrachain conduction mechanism exclusively without the interference from the interchain one as well as information on a close correlation between the conduction mechanism and the main-chain conformation. It is clearly revealed that there exist two kinds of transport of carriers along the polymer chain with different diffusion distances and diffusion constants.

The applied electric field dependences of the field-induced tilt angle and electric displacement are studied in the SmA phase of a ferroelectric liquid crystal. The electroclinic constant and nonlinear dielectric constants obtained from the measured data increase in their magnitude on approaching to the SmA-SmC phase transition temperature. The temperature dependences of these constants are in a good agreement with those predicted by the phenomenological theory of Landau type for the phase transition, and the phenomenological parameters appearing in the theory can be determined from these constants.

The non-linear dielectric relaxation spectroscopy has been recently developed and applied to soft materials such as polymers. We have applied this new method to the S*C phases of some ferroelectric liquid crystals. Under a weak AC electric field, the original and third order harmonic frequency components of electric displacement are proportional to the first and third powers of the applied electric field, respectively. The linear spectrum obtained from the original frequency component shows the relaxation of Debye type and the third order non-linear spectrum shows the relaxation with an extended form of Debye type to the non-linear case. The third order non-linear dielectric increment is found to be negative, which implies that the dielectric non-linearity of the liquid crystal in the S*C phase is due to the saturation of molecular dipole moments induced by the applied electric field. The temperature dependence of the linear and third order non-linear spectra in the S*C phase are also studied. Bo...

The local and slow dynamics of a colloidal particle dispersed in a hyperswollen lyotropic lamellar phase was studied by passive and active microrheological methods. According to observation by a particle-tracking video microscopy, the motion of a particle follows a normal diffusion process in a lamellar phase with a large interlayer distance. However, trap-diffusion motion was also observed for a small interlayer distance. This characteristic motion was discussed by consideration of the time evolution of mean square displacement, the van Hove self-correlation function and the non-Gaussian parameter. These indicate that the dynamics of a particle becomes spatially heterogeneous in a lamellar phase whose interlayer distance is close to the size of the particle. By the measurement of local viscosity using optical tweezers, Newtonian behavior was observed at a high shear rate. In a lamellar phase with a small interlayer distance, non-Newtonian behavior was also observed at a low shear rate. The dependences of effective viscosity on the interlayer distance obtained by both methods are in agreement. The effective viscosity in the lamellar phase was found to be four to five times larger than that of water even for a large interlayer distance. Possible reasons for the increase in effective viscosity are discussed quantitatively.

We have experimentally studied the interparticle force between two particles accompanied by hyperbolic hedgehog defects in a nematic liquid crystal. The force $F$ was measured with dual-beam optical tweezers at various temperatures and in cells with various thicknesses. In a thick cell, the dependence of $F$ on the interparticle distance $R$ obtained at different temperatures can be scaled to a universal curve of $F\ensuremath{\propto}{R}^{\ensuremath{-}4}$ for $Rg3a$, where $a$ is the radius of a particle. The effective elastic constant evaluated from $F$ is found to be in good agreement with splay constant of the nematic liquid crystal. In a thin cell, the magnitude of $F$ decreases and the dependence of $F$ on $R$ becomes short-ranged as the thickness of a cell, $L$, decreases. The reduced force curves, $F{L}^{4}$ against $R/L$, at different $L$ are found to be scaled to a single theoretical curve which has been proposed recently.

We studied the conformation and dynamics of a single DNA molecule in a thin slit by a fluorescent microscope. In a slit thinner than the Flory radius in three dimensions, the length of the major axis, the translational self-diffusion coefficient and the rotational relaxation time in a dilute solution show the apparent dependence on the thickness of the slit. The observed dependence is in agreement with that predicted by blob theory, despite the number of blobs is very small. The radial distribution of the segments around the center of mass of a single molecule was also studied and compared with that calculated for a Gaussian and an excluded volume chain. The influence of the polymer concentration on the geometrical confinement by slits was also studied in a semidilute solution near the overlap concentration c*. The confinement effect is found to be not so serious near c * and is only significant in the so-called "two-dimensional pancake" region.