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Kaoru Tsujii

Publications and source records attributed to Kaoru Tsujii.

13 recordsLinked to original sources
PubMed2006

Effect of ionic surfactants on the iridescent color in lamellar liquid crystalline phase of a nonionic surfactant.

A nonionic surfactant, n-dodecyl glyceryl itaconate (DGI), self-assembles into bilayer membranes in water having a spacing distance of sub-micrometer in the presence of small amounts of ionic surfactants, and shows beautiful iridescent color. Ionic surfactants have strong effects on this iridescent system. We have interestingly found that the iridescent color changes with time after mixing DGI and ionic surfactants and the color in equilibrium state changes greatly with concentration of the ionic surfactants. The time-dependent color change results from the transformation of DGI aggregate structure after being mixed with ionic surfactant. It is first found that the iridescent color of this nonionic system can be changed from red to deep blue by altering the concentration of ionic surfactants added even though the total concentration of surfactant is almost constant. Such large blue shift of the iridescent color in equilibrium state cannot be fully explained by the ordinary undulation theory applied so far for this phenomenon. The flat lamellar sheets tend to curve by increasing the concentration of ionic surfactants to form separated onion-like and/or myelin-like structures. These separated structures of lamellar system result in the decrease of spacing distance between bilayer membranes because some vacant spaces necessarily appear among these structures.

Journal Article↗
PubMed2006

Viscosity measurements of water at high temperatures and pressures using dynamic light scattering.

The application of dynamic light scattering to measure viscosity of water at high temperatures and pressures is demonstrated. Viscosity was obtained from the translational diffusion coefficient of probe particles dispersed in the medium by the Einstein-Stokes relationship. Measurements were carried out with polystyrene latex, colloidal silica, and colloidal gold. Under a constant pressure of 25 MPa, good agreement was found between the measured and calculated viscosities up to 275 degrees C with the polystyrene latex, 200 degrees C with the colloidal silica, and 297 degrees C with the colloidal gold. It was found that failure of the measurements at high temperatures is ascribed to change in either the dispersion stability or chemical stability of the probe particles. The present results indicate that the technique could also be used for other supercritical fluids having high critical temperature and pressure, such as methanol (T(c) = 239.4 degrees C, P(c) = 8.1 MPa) and ethanol (T(c) = 243.1 degrees C, P(c) = 6.4 MPa).

Chemistry, Physical↗
PubMed2006

Adsorption of microstructured particles at liquid-liquid interfaces.

The solid particles are adsorbed at interfaces and form self-assembled structures when the particles have suitable wettability to both liquids. Here, we show theoretically how the microstructure on the particle surface affects their adsorption properties. The physical properties of the interface adsorbing a particle will be described by taking into account the surface roughness due to the microstructure. The microstructure on the surface changes drastically the wettability and the equilibrium position of the adsorbed particle. Therefore, the contact angle of the particle at the three-phase contact line shifts with the particle surface area, because the surface roughness enhances the interfacial properties of the particle surface. Moreover, the range of the interfacial tensions at which the particle is adsorbed becomes narrower with the increase of the surface roughness. The effect of the particle shape on the adsorption properties is also studied. In the case of disk-shaped particles, the energy changes discontinuously when the plane surface of the particle contacts the liquid-liquid interface. The adsorbing position does not change with the surface roughness. The orientation of a parallelepiped particle at the liquid-liquid interface is governed by the aspect ratio and the surface area of the particle. On the other hand, the particle which is partially covered with the microstructured surface is adsorbed firmly at the interface in an oriented state. We should consider not only the interfacial tensions but also the surface structure and the particle shape to control the adsorption behavior of the particle.

Journal Article↗
PubMed2006

Premicellar aggregation of fatty acid N-methylethanolamides in aqueous solutions.

The aggregation behaviors of an excellent nonionic foam booster, namely, fatty acid N-methylethanolamide (NMEA-X; X indicates the carbon number of the acyl group), in aqueous solutions have been studied by equilibrium surface tension (gamma), solubilization of oil-soluble dye, and steady-state fluorescence techniques. NMEA, having a longer alkyl chain than NMEA-08, clearly had two break points on the gamma versus log C (where C is concentration) curves. The solubilization of the oil-soluble dye for NMEA aqueous solutions began at the break point of higher concentration in the gamma versus log C curves, so this concentration was confirmed to be the critical micellization concentration (cmc). Above the cmc, however, a separate oil phase of NMEA was observed instead of micelles of limited size. Another break point at lower concentration was also observed in plots of the fluorescence intensity ratio of pyrene, I1/I3, versus log C of NMEA. The gradual decrease of I1/I3 and the appearance of excimer emission of pyrene in the concentration region between the two break points suggest the existence and growth of premicellar aggregates and the solubilization ability of pyrene. Consequently, this break point at lower concentration was assumed to be the critical premicellization concentration (cac). The surface tension reduction in the premicellar region decreased with increasing alkyl chain length of NMEA.

Journal Article↗
PubMed2005

Potential application of poly(N-isopropylacrylamide) gel containing polymeric micelles to drug delivery systems.

We have investigated rapidly thermo-responsive NIPA gel containing polymer surfactant PMDP (NIPA-PMDP gel) as a potential drug carrier using (+)-l-ascorbic acid as a model drug. In the NIPA-PMDP gel system micelles of polymer surfactant PMDP are trapped by the entanglement of polymer chains inside the gel networks. Therefore, in principle the gel system tightly stores targeted drug in the micelles and rapidly releases controlled amount of the drug by switching on-off of external stimuli such as temperature or infrared laser beam. In our investigation on release profile, the NIPA-PMDP gel system showed completely different releasing behavior from that of the conventional NIPA gel. The NIPA-PMDP gel released rapidly all loaded (+)-l-ascorbic acid above the phase transition temperature (ca. 34 degrees C), while slowly released the corresponding amount of the drug below the temperature. In contrast, the conventional NIPA gel released more slowly limited amount of the drug above the phase transition temperature while similarly did to the NIPA-PMDP gel below the temperature. The release profile of the NIPA-PMDP gel seems to be governed by only kinetics of volume phase transition of the gel network but not by the hydrophobic domains of the micelles probably because of too hydrophilic nature of (+)-l-ascorbic acid.

Acrylic Resins↗
PubMed2005

Surface-active particles with microstructured surfaces.

Interfaces adsorbing solid particles have recently attracted great attentions in the field of materials science, because they are useful as templates of well-ordered particle arrays or of microstructured hollow spheres. The solid particles are adsorbed at the interfaces and form self-assembled structures when the particles have suitable wettability to both fluids. Here, we show theoretically how the microstructure on the particle surface affects their adsorption properties. The physical properties of the interface adsorbing a particle will be described with consideration for surface area magnification due to the microstructure. The microstructure on the surface changes drastically the wettability and the equilibrium position of the adsorbed particle and prevents the particle from adsorption at the interface. The range of the interfacial tensions at which the particle is adsorbed becomes narrower with the increase of the magnification. On the other hand, the particle which is partially covered with the microstructured surface is adsorbed firmly at the interface in an oriented state. We should consider not only the interfacial tensions but also the surface structure to control the adsorption behavior of the particle.

Journal Article↗
PubMed2005

Template-guided synthesis and individual characterization of poly(N-isopropylacrylamide)-based microgels.

We have succeeded in making cylindrical PNIPA-based microgels by a novel strategy in which template-guided synthesis and photochemical polymerization were combined. Cylindrical PNIPA-based microgels of relatively uniform sizes were easily obtained corresponding to the pore size of the template PC membranes. We have also individually characterized our PNIPA-based microgels by a laser trapping/Raman spectroscopy technique. On the basis of these results, the individual microscopic objects were confirmed to be PNIPA-based microgels.

Journal Article↗
PubMed2005

Chemical toxicity of indocyanine green damages retinal pigment epithelium.

PURPOSE: To investigate the chemical toxicity of indocyanine green (ICG). METHODS: Surface active and precipitating effects of ICG were quantitatively analyzed by determining bovine serum albumin dissolved or precipitated in the presence or absence of salt solutions. The effects of precipitation on serum and cytotoxicity were evaluated by measuring the viability of retinal pigment epithelium (RPE) in vitro. RESULTS: ICG functioned as a surfactant without salts, but with nearly physiological concentrations of balanced salts, it functioned as a unique precipitating factor. This rendered the soluble molecules in serum that are indispensable in the culture of RPE cells insoluble during a 12-hour exposure, resulting in poor cell survival in vitro. Cytotoxicity in serum-free medium was also shown during brief exposures. CONCLUSIONS: Commonly used dosages of ICG directly applied into the vitreous cavity, which not only contact the retina but also invade the space between the retina and RPE through a macular hole, may be sufficient to induce retinal disorders after the damaging chemical property of ICG has disturbed the microenvironment.

Acetates↗
PubMed2002

Reaction behaviors of glycine under super- and subcritical water conditions.

The influence of temperature and pressure on the dimerization and decomposition of glycine under simulated hydrothermal system conditions was studied by injecting a glycine solution into water in the sub- and supercritical state. The experiments at five different temperatures of supplied water--250, 300, 350, 374, and 400 degrees C--were performed at 22.2 and 40.0 MPa. At 350 degrees C, experiments under 15.0-40.0 MPa were conducted. Diglycine, triglycine (trace), diketopiperazine, and an unidentified product with a high molecular mass (433 Da) were the main products of oligomerization. The results show that temperature and pressure influence the extent of dimerization and decomposition of glycine. The maximum of dimers formation was observed at 350 and 375 degrees C at 22.2 and 40.0 MPa, respectively, and coincided with a high rate of glycine decomposition. Glycine, alanine, aspartic acid, as well as other amino acids, were obtained by injecting a mixture of formaldehyde and ammonia. The results support the oligomerization and synthesis of amino acids in a submarine hydrothermal system.

Amino Acids↗