Search

The formation of submicron polystyrene (PS) particles based on dewetting process during spin-coating was investigated. The surface morphologies on glass substrates were analyzed. The formation of particles was achieved using PS with relatively high molecular weight (Mw ≥ 3250). In addition, it was observed that the particle formation proceeded through sequential morphological changes in the order of initial wet thin film, secondary spinodal-decomposed structures, and eventual dewetted particles. One of the fabricated samples exhibited obvious optical resonance in the visible region based on the relationship between particle dimeters and optical wavelengths in the visible region. The optical resonance strongly depended on the ambient refractive index, which can be used for optical sensor-chips. Finally, a multi-functional biosensor-chip was demonstrated to detect glucose in water solutions.

A high-density array of barnacle-like porous structures was fabricated using monolayers of polystyrene spheres and various types of poly(vinyl alcohol). We first prepared the polystyrene sphere monolayer as a close-packed hexagonal array on a glass substrate. The monolayer was then etched using a plasma treatment to isolate each sphere. Next, we spin-coated the isolated spheres with a water solution of poly(vinyl alcohol). After drying, we applied a second short plasma treatment to the substrate before immersing it in a toluene bath, which promoted opening formation due to polystyrene swelling. As a result, a high-density array of barnacle-like porous structures was homogenously formed on the substrate. These porous structures are expected to be used for various applications including functional coatings, protective cell cultures, and sensor chips.

Low-temperature radical polymerization of achiral N-allyl-N-tert-butylacrylamide (AltBAAm) was conducted in toluene in the presence of chiral tartrates, such as diethyl l -tartrate (L-EtTar) and di-n-butyl l -tartrate. The 1H NMR spectra of the polymers obtained indicated progress of cyclopolymerization at low temperatures such as −80 °C. Optical properties of the poly(AltBAAm)s examined by optical rotation and circular dichroism measurements indicated asymmetric induction in the cyclopolymerization of achiral AltBAAm. For example, addition of L-EtTar at −80 °C provided the polymer with specific rotation of −4.8°. The tert-butyl groups of poly(AltBAAm)s were removed by treatment with CF3SO3H, transforming into poly(N-allylacrylamide)s [poly(AlAAm)s]. Then, stereochemistry in the stereorepeating unit was investigated by comparing 1H NMR signals of the poly(AlAAm)s with those of model compounds, cis- and trans-3-ethyl-4-methyl-2-pyrrolidones. Taking the negative specific rotation values of the poly(AltBAAm)s obtained with L-tartrates into account, it was revealed that (3S,4S)-trans-unit was predominantly formed through the hydrogen-bond-assisted complex formation of AltBAAm with L-tartrates.

A first-order beam diffracted by periodic arrays of GMR structures consisting of Pt/Co free layers having perpendicular magnetization without a top electrode is investigated. Linear and two-dimensional arrays of various shapes having sizes of 10–50 μm and periods of 20–100 μm embedded in SiO 2 are fabricated. The angles of the plane of polarization for first or (1,0) diffraction spots at a wavelength of 633 nm are measured to be approximately 0.5° for all samples. The polarization angles for one- and two-dimensional arrays of magnetic patterns are studied theoretically by assuming that the structures have sinusoidal magnetic distributions. They are found to depend on the Kerr rotation angle of the Pt/Co multilayer and on the difference in reflectance between the Pt/Co and SiO 2 , but they are independent of the periodicities, sizes, and shapes of the patterns. On the other hand, the diffraction efficiencies due to the magneto-optical effect depend on the reflectance and Kerr rotation angles of the magnetic materials. The diffraction efficiency of the component arising from the magneto-optical effect is discussed.

In this work, we report on a dichroic reflection phenomenon in the specular direction. The reflective medium is an Au-coated anisotropic hemispherical structure (AuAHeS), composed of a polymer material, which is fabricated via a replication process based on a polystyrene (PS) spherical particle array monolayer. Structural anisotropy is provided artificially by stretching the silicone rubber mold used in the replication process. Depending on the anisotropy of the resulting structure, the absorbance spectra are significantly altered for incident light that is polarized either parallel or perpendicular to the stretching direction. Based on the optical characteristics of the structures observed in the present study, the generation of unique devices for optical, photonic, and bio-photonic applications is expected to be possible.

Self-assembling of binary colloidal crystals (bCCs) consisting of spherical particles with different diameters has been used for monolayer fabrication in glass cells. The procedure involves two crystallization steps. Upon crystallization of a colloidal suspension containing large spheres, a monolayer is formed on the bottom substrate of the cell. Then, a colloidal suspension containing small spheres, which assemble in the interstitial parts between the large spheres, is injected into the cell. The resulting bCC monolayers are characterized using scanning electron microscopy (SEM) and reflection spectroscopy. Reflection spectra reflect the bCC structure and forbidden bands corresponding to the grating constant of the second colloidal crystal. The structure and optical properties of the bCC monolayer can be specified depending on the ratio of the diameters of the spheres. The proposed process for bCC monolayer fabrication is extremely simple, and therefore ideal for practical uses.

Surface relief (SR) gratings with a molecularly oriented structure and pure polarization hologram were fabricated on a photo-cross-linkable liquid crystalline copolymer using a 325-nm laser with various two-beam polarization modes. For intensity holography, the polarization information from the two beams simultaneously provided the molecular motion and molecular reorientation; the SR height reached up to 186 nm and the concave area revealed a molecular reorientation when the exposing beams were linearly polarized. In contrast, SR formation was negligible for polarization holography when molecular reorientation due to the polarization modulation was observed. The resulting polarization gratings changed the polarization properties of the diffraction beams, and their diffraction efficiency was reached 24%, which agreed with theoretical expectations.

A new photo-cross-linkable liquid crystalline polymer (PLCP) comprised 4-methoxycinnamoyloxy groups connected with a bistolane side group was synthesized to investigate thermally enhanced photoinduced molecular reorientation of a thin film with linearly polarized (LP) 365 nm light exposure. Due to the axis-selective photoreaction of the cinnamate groups followed by the thermally induced self-organization, large molecular reorientation parallel to the polarization of LPUV light ( S > 0.6) and large birefringence at the non-resonance region (Δ n = 0.34 at 632.8 nm) were obtained. The obtained Δ n value is the largest among transparent PLCPs in the visible region. The influence of the degree of photoreaction and the annealing temperature on the thermally enhanced molecular reorientation behavior was explored in detail. Finally, for an application of thin optical devices using the PLCP films, pure polarization holographic gratings with large birefringence, which showed periodic molecularly oriented structure, were fabricated using a 325 nm He–Cd laser in various polarization modes and characterized their optical properties.

Effects of recording wavelength on the recently proposed (Sasaki, 2008) three-dimensional vector holograms, in which the optical anisotropy is three-dimensionally modulated, are presented experimentally and theoretically. The polarization states of the interference light are three-dimensionally modulated due to both the polarization interference and optical anisotropy in the recording medium. These spatial distributions of the polarization states and the resulting diffraction properties in the three-dimensional vector holograms are strongly dependent on the recording wavelength. Theoretical consideration based on the finite-difference time-domain (FDTD) method reveals the mechanism of the optical characteristics of the three-dimensional vector holograms recorded by various kinds of light sources with different wavelengths.

We present the results from some experimental and theoretical studies aimed at revealing the mechanism leading to the diffraction properties of two-dimensional cross polarization gratings in photocrosslinkable polymer liquid crystals. Although the polarization gratings are overwritten at the same place, each polarization grating works independently in our material system. The above-mentioned characteristic of our cross polarization gratings originates in the grating formation mechanism in the photocrosslinkable polymer liquid crystals, in which the molecules in the solid-state polymeric materials are not reoriented during exposure and reorientation is generated during the annealing process after multiple exposure.

We have presented the results of some experimental studies aimed at quantifying the anisotropic holographic recordings in photoreactive polymer liquid crystals. In addition to the surface-relief gratings, index modulation gratings also appear during the holographic recording process, and the resulting dual gratings with strong anisotropy were characterized using the diffraction theory. The index modulation gratings showed strong optical anisotropy although the gratings were recorded by means of intensity holographic technique with only circularly polarized light. The experimental results including the induced birefringence were explained on the basis of the molecular migration.

Optical image reconstruction, a type of intensity amplification of a two-dimensional optical image, was demonstrated using photorefractive polymer-dissolved liquid crystals. Image amplification originated in nonlocal gratings generated in a photorefractive mesogenic composite consisting of a low-molar-mass nematic mixture, a functionalized copolymer, and sensitizing dye. This process was well-explained using Fourier optics and two-beam coupling theory for photorefractive effects.

Effects of liquid-crystal droplet size on orientational photorefractive properties of the polymer dispersed liquid crystals are investigated experimentally. The composites consist of the same chemical components, but the liquid crystal droplet size was varied by controlling the fabrication process. Particular attention is given to the observation and qualitative and/or quantitative modeling of the resolution, dependence of the applied dc field, dynamics of grating generation and photocurrents, which is strongly dependent on the liquid crystal droplet size.