APPLICATION OF LAYERED INORGANIC MATERIALS IN RECTIFICATION OF ELECTRO-OPTICAL PROPERTIES OF NEMATIC LIQUID CRYSTALS AND POLYMER-ENCAPSULATED LIQUID CRYSTALS
TSUNG-YEN TSAI, CHUN-YI LEE and WEI LEE
The electro-optical (EO) properties were measured for cells composed of layered inorganic materials; i.e., either the smectite sodium montmorillonite (MMT) or layered double hydroxides (LDHs), as an additive in the organic nematic liquid crystal (NLC) E7 or blends of E7 and a photoinduced polymer. For a twisted NLC (TNLC) device driven by an applied voltage, the smectite hybridized into the LC was found to suppress the formation of electric bilayers and the field-screening effect, significantly reducing the ion-charge concentration down to as low as ~1% for a TNLC-clay cell containing ~0.5 wt% MMT1, 2). Similar results were also observed from the LC-clay nanocomposite confined in a homogeneously-aligned cell3). On account of the clay platelets and NLC molecules being aligned by the externally applied voltage and the nanoplatelets homogeneously dispersed in the NLC hydrosol, the voltage-transmittance curve of the hybrid cell exhibited increasing contrast ratio of the LC photonic device. Besides, the voltage-capacitance characterization indicated that the layered inorganic clay in E7, depending strongly on the proper charge properties such as charge affinity of the layered materials itself, was able to dramatically decrease the threshold voltage for cells of TNLC-clay composites operated by dc electric field. Consequently, adding an appropriate amount of clay substantially rectified the EO switching properties of a typical low-resistivity NLC in the TNLC-clay hybrid materials system.
On the other hand, holographic polymer-dispersed LCs (H-PDLCs) consisting of E7 and layered inorganic materials in photo-polymerized macromolecular matrices were investigated. The H-PDLC were fabricated from a monomer hybrid solution including dipentaerythritol pentaacrylate (SR399), cross-linking N-vinylpyrrollidone (NVP), photo-initiator dye Rose Bengal (RB), co-initiator N-phenylglycine (NPG) and E7 by wave mixing of two coherent argon-ion laser beams at the 514.5 nm line4, 5). Due to the photo-induced polymerization phase separation, the NLC-polymer blends were separated into mesophase and polymer phase and the role of clay as a dopant in the phase separation processes could be established by observing the morphologies of the composite films and the resulting performance of the cells. The effect of MMT doping in the NLC-polymer systems was first revealed by the wide-angle X-ray diffraction pattern, indicating that the liquidcrystalline signal was enhanced by doping various clays at adequate contents. Further evidence was manifested by the increases in both the range of the size distribution and the maximum size of the NLC droplets with increasing clay content up to 3 wt%, as examined with a transmission electron microscope as well as a field-emission scanning electron microscope after the cell substrates were taken apart and E7 droplets was removed from the PDLCs4, 6). We found the PDLC comprising 3 wt% clay with higher cation exchange capacity (168 meq per 100 g of clay in this study) to be dramatic in particular to lower the driving voltage, switching time and threshold voltage simultaneously and to suffer less serious off-axis haze at large angles of incidence in general6). For H-PDLCs, self-diffraction experiments in the Raman?Nath regime showed that the first-order diffraction efficiency was enhanced in those consisting of pristine MMT nanoparticles and yet depressed by the incorporation of organophilic MMT5). Holographic nature of the nanocomposites with polymeric matrices was confirmed by optical polarizing microscopy4, 5). Without the use of an applied voltage, the 5-phr-clayhybridized and 1-phr-LDH-doped nanocomposites yielded the improved first-order diffraction efficiencies of 6 times and 4 times higher than that of the pristine H-PDLC counterpart, respectively5, 7). In contrast, the diffraction efficiency of the phase gratings recorded in the cells of E7 hybridized with 1 wt% MMT clay was found to be only three times higher than that in the pristine cell when a dc electric field of 0.5 V/Êm was applied.
NANOKAOLIN: PROPERTIES AND APPLICATION
QINFU LIU, YUDE ZHANG, LEIBO JI and QIAN ZHANG
A kind of nanokaolin (abbreviated as NK) with 20|50 nm average thickness, 300|500 nm average diameter and 32 m2/g specific surface area, was successfully commercialized to apply in rubbers for the reinforcing fillers. The nanokaolin was manufactured through a series of procedures, which are purification, size separation, exfoliation, surface modification and spray drying. A serial of rubber nanocomposites with nanokaolin and precipitated silica (abbreviated as PS) were prepared by traditional method of melt blending process. The properties of nanokaolin and the rubber nanocomposites were characterized. The results showed that this kind of nanokaolin had better enhanced performance and gas barrier property compared with the precipitated silica.
SIZE FRACTIONATION OF CLAY AND SOIL MICROPARTICLES BY CONTINUOUS-FLOW ULTRACENTRIFUGATION
TOMOYUKI MAKINO, MAKI INADA, TAKAHISA KATO, YASUHISA ADACHI and MASATAKA MORITA
Continuous-flow ultracentrifugation (CFUC) was used to separate soil microparticles (SMP) on the basis of theoretical particle size (Stokesf law), and the results were compared with those from swing rotor centrifugation. Clay and soil particles were clearly separated on the basis of theoretical particle size, which was confirmed by a laser-scattering particle-size distribution analysis. These results indicate that CFUC is useful for size fractionation of SMP.
TEN-YEAR INTERACTION OF CARBON STEEL COUPON AND COMPACTED BENTONITES
KENICHI UENO, TADAHIRO SUYAMA, TAKAMITSU ISHIDERA, TSUTOMU SATO
In the Japanese high-level waste (HLW) repository design, compacted bentonite and carbon steel overpack are the main components of the engineering barrier system. The possibility that the chemical and physical properties of the compacted bentonite might change after interaction with corrosion products of the carbon steel has been noted. Experimental validation of the interaction of smectite in compacted bentonite as simulated in the HLW repository system is still very limited. This study focuses on smectite and corrosion product interaction and Fe migration behavior in compacted bentonite systems.
In this study, the alteration of smectite that was in contact with carbon steel for 10 years was investigated by X-ray diffraction, and Fe migration behavior was observed by electron probe micro-analysis (EPMA). Smectite interstratification was observed only in an experiment using synthetic sea water at 80C; in this experiment, cation exchange in which the original Na+ changed to Fe2+ was also observed. The apparent diffusion coefficients were calculated from the Fe profile measured by EPMA. The values were smaller than those reported in the literature, indicating not only a pure diffusion process but also contributions from precipitation and porosity reduction.
The experimental results were also modeled using the calculated apparent diffusion coefficients to investigate Fe migration properties and the stability of minerals in compacted bentonite. The calculated and observed smectite stability and precipitation behavior of mineral phases were in agreement. However, the total number of cation exchange sites and the amount of Fe distribution were not well described and were significantly affected by a transient state early in the experiment.
ORGANO-SMECTITE ADSORBENTS; DESIGNED NANOSTRUCTURES FOR SMART ADSORBENTS
TOMOHIKO OKADA, and MAKOTO OGAWA
Organically modified clays have been investigated as adsorbents, catalysts and their supports, in addition to the commercialized uses such as rheological ones. In the present review article, recent developments of smart adsorbents with such optical responses as sensing of aromatic compounds and photoinduced adsorption/reaction are overviewed with emphasis on our contribution. The adsorbents have been designed by tuning nanostructures through the surface modification with organic functionalities. Selection of organic cations and the spatial distribution are important points to construct adsorbents, recognizing nonionic aromatic compounds both from aqueous solutions and from vapor phase. In addition to the organoclays, several examples of the optical sensing based on smectite without organic functionality are also introduced in this review.