Viscoelasticity of a dielectric fluid in nonuniform electric fields generated by electrodes with flocked fabrics

The rheological behavior of a dielectric fluid is studied in nonuniform electric fields which are generated by an electrode covered with flocked fabrics. Although no electrorheological (ER) effects are observed in uniform fields between metal electrodes with smooth surfaces, striking increases in viscosity and elastic response are induced by the electrode with flocked fabrics. The presence of flocked fabrics does not have a significant effect on the fluid rheology without electric fields. The ER behavior and current density are influenced by the fiber length even at a constant field strength. When a very small amount of fine particles is introduced in the electrified fluid without shear, we can see the rapid and large-scale motion of particles between the tips of fibers and plate electrode. In high DC fields, the Coulomb force acting on a free charge often gives rise to the secondary motion of fluid. The local motion of fluid in high electric fields is refereed to as electrohydrodynamic (EHD) convection. The additional energy may be required to change the periodic patterns of EHD convection by forced shear. Therefore, the ER effect demonstrated by the modification of electrode with flocked fabrics can be attributed to a combined effect of EHD convection and external shear. Received: 10 March 1998 Accepted: 1 June 1998     

Bioluminescence-based imaging technique for pressure measurement in water

The dinoflagellate Pyrocystis lunula emits light in response to water motion. We developed a new imaging technique for measuring pressure using plankton that emits light in response to mechanical stimulation. The bioluminescence emitted by P. lunula was used to measure impact water pressure produced using weight-drop tests. The maximum mean luminescence intensity correlated with the maximum impact pressure that the cells receive when the circadian and diurnal biological rhythms are appropriately controlled. Thus, with appropriate calibration of experimentally determined parameters, the dynamic impact pressure can be estimated by measuring the cell-flash distribution. Statistical features of the evolution of flash intensity and the probability distribution during the impacting event, which are described by both biological and mechanical response parameters, are also discussed in this paper. The practical applicability of this bioluminescence imaging technique is examined through a water drop test. The maximum dynamic pressure, occurring at the impact of a water jet against a wall, was estimated from the flash intensity of the dinoflagellate.     

pH- and H2O-driven triple-mode pyrene fluorescence

[reaction: see text] A simple-structured molecule L1, a diethylenetriamine bearing two end pyrene fragments, demonstrates triple-mode fluorescence consisting of monomer and short- and long-lived excimer emissions in water, which are precisely controlled by pH and an addition of a less-polar organic solvent.     

Synthesis of (+)-galantinic acid,a constituent amino acid in the peptide antibiotic galantin I, via the stereoselective epoxidation of a chiral serine equivalent

Epoxidation of (2$\text{R}$)-$\text{t}$-butoxycarbonylamino-3-butenol afforded, in a highly stereo-selective manner, a $\text{threo}$-3,4-epoxy-2-aminobutanol derivative which was successfully converted to the unusual amino acid (+)-galantinic acid in 8 steps $\text{via}$ regiospecific epoxide ring opening with divinyl cuprate.     

Electrorheological toners for electrophotography

The electrorheological (ER) behavior of pigment suspensions dispersed in a nonaqueous solvent was examined for their application as liquid toners for electrophotography. In electric fields, particles can align into chains along the field vector by dielectric polarization forces and the suspensions undergo a rapid transition from Newtonian fluids to Bingham bodies. However, the migration and deposition of particles can take place by the electrophoretic effect, because charge control agents are added to liquid toners for fast development. The combined effects of dielectric polarization forces, electrophoretic forces, and hydrodynamic forces make rheological behavior very complicated. To simulate the ER behavior of liquid toners in reprographic processes, viscosity measurements were carried out in electrodes with a honeycomb pattern. Nonuniform electric fields enhance the dipole-dipole interactions between particles and give rise to a striking ER effect. Based on measurements in honeycomb pattern electrodes, new ER toners were developed which can reproduce images with high quality.     

Electrochemical Quantitative Evaluation of the Surface Charge of a Poly(1-Vinylimidazole) Multilayer Film and Application to Nanopore pH Sensor

Nanopore pH sensing is based on the interaction between the surface charge of the nanopore and ions passing through the nanopore. The nanopore surface charge can be derived from the acid-base dissociation equilibrium of the modified polyelectrolyte. Various polyelectrolytes have been selected based on the acid dissociation constant of the monomer units, and various techniques have been applied to modify nanopores. However, they have been developed without clear guidelines for characterizing the surface modification status or surface charge. One reason has been the difficulty in accurately estimating the surface charge of nanopores in solution. Thus, in this study, the dissociation constant (pKa_app) of the surface charge of a modified polyelectrolyte nanopore was quantitatively estimated via electrochemical measurements. Previously, the modification status of nanopores has been evaluated using the ion current response. In addition, we monitored in real-time the polyelectrolyte modification status using a quartz crystal microbalance (QCM). Some polyelectrolytes were difficult to immobilize directly on the nanopore surface, and those polymers could be effectively modified by the layer-by-layer (LbL) technique. Therefore, we produced a guideline for the fabrication of a nanopore sensor for pH measurements under physiological conditions by quantitative evaluation of the pKa_app via electrochemical methods, the monitoring of the modification status by QCM, and the development of an effective modification method via the LbL technique.     

Selective transformation of N-t-butoxycarbonyl group into n-alkoxy-carbonyl group via n-carboxylate ion equivalent

Reaction of a variety of N-$\text{t}$-butoxycarbonyl compounds with $\text{t}$-butyl-dimethylsilyl trifluoromethanesulfonate afforded the N-$\text{t}$-butyldimethyl-silyloxycarbonyl compounds, chemoselectively, which upon treatment with an alkyl or aryl halide provided the corresponding N-alkoxy- or N-aryl-oxycarbonyl compounds, efficiently.