Anomalous long-range repulsion between silica surfaces induced by density inhomogeneities in supercritical ethanol.

Anomalous long-range repulsion, extending over several micrometres, emerged between silica surfaces around the ridge of density fluctuations in supercritical ethanol at temperatures and pressures near the gas/liquid critical point (T(c) = 241 °C, P(c) = 6.14 MPa). Analysis shows that augmentation of ethanol density around silica surfaces in the presence of density fluctuations facilitates dissociation of silanol groups, leading to long-range electrostatic repulsion in the nonpolar medium.

Unique diffusion behavior observed in supercritical ethanol.

We have systematically investigated the diffusion behavior of silica nanoparticles within supercritical ethanol, in terms of solvent properties by varying temperature (T) and pressure (P), to elucidate how the inhomogeneous solvent structures and density fluctuations in the solvent affect the diffusion behavior of solute particles. Results show that at a constant pressure, the diffusion coefficient (D) of the particles increases with increasing temperature, reaches the maximum (D(max)) within the gaslike supercritical fluid (slightly below the ridge), and finally decreases abruptly at very low fluid density when temperature is increased further. Results reveal that D is appreciably larger than the theoretical prediction (Einstein-Stokes relationship) in the vicinity of the critical density (rho(c)) of the solvent. We interestingly observed that D becomes maximum (D(max)) at a particular thermodynamic condition (T(i),P(i)), which is expressed by the empirical formula T(ri)=P(ri) (0.16) (for T(ri)>1, P(ri)>1). Here, T(ri)=T(i)/T(c) and P(ri)=P(i)/P(c); T(c) and P(c) are the temperature and the pressure at critical point, respectively. Results further reveal that D(max) increases significantly with decreasing solvent density within the gaslike supercritical fluid where the changes in viscosities are negligible. These findings are unique, novel, and intriguing. We suggest that the enhancement of the diffusion coefficient in the vicinity of the critical density and the abrupt decrease in the diffusion coefficient in very low density gaslike fluid are associated with the change in the solvent-solvent and solute-solvent direct correlation function (related to the effective interaction potential) upon density change when the fluid crosses the ridge of density fluctuations and within the gaslike fluid.

Versatile solidified nanofibrous cellulose-containing media for growth of extremophiles.

Solidified media that employ a porous matrix of nanofibrous cellulose are described. The physicochemical stability of the porous structure allows the development of solidified media that can support the growth of extremophiles, such as acidophilic Acidiphilium, alkaliphilic Bacillus, thermophilic Geobacillus and Thermus, alkalithermophilic Bacillus, and acidothermophilic Sulfolobus microbes. The cellulose-supported media have several advantages over agar- and gellan gum-derived media, including versatility and stability.

Spontaneous formation of super water-repellent fractal surfaces in mixed wax systems.

Alkylketene dimers (AKDs) and triglyceride waxes form fractal surfaces spontaneously and show super water-repellent property. Spontaneous formation of fractal structures on their surfaces takes place when the meta-stable crystalline phase of the waxes transforms to the thermodynamically stable form of crystal. The triglyceride waxes form the meta-stable alpha-phase in whole specimen when solidified from their melt. In the case of AKD, on the other hand, only a small portion of the specimen solidifies in the meta-stable form of crystal. The surface of the AKD, however, becomes fractal in the whole part. We have, thus, examined the fractal structure formation in the mixed wax systems in which one wax forms fractal surfaces and the other one does not. In the stearic acid/tristearin mixed system as a typical one, the super water-repellent fractal surfaces form in the higher composition region of tristearin than that of the eutectic point in their mixture.

Effect of pressure on colloidal behavior in hydrothermal water.

The pressure dependence of the colloidal phenomena of nanoparticles in hydrothermal water was investigated by both experiment and theory. Dynamic light scattering experiments show that diamond nanoparticles, which are highly stable in ambient water, easily aggregate in high-temperature and high-pressure water. Although the stability of nanoparticles in ambient pure water does not depend on pressure, it is interestingly found that at constant temperature particles aggregate faster in the hydrothermal regime when the pressure is higher. A theoretical interpretation is proposed to predict the stability of colloids in water as a function of temperature and pressure. Numerical analysis shows that the repulsive interparticle potential barrier, which stabilizes particles in the dispersion, decreases dramatically in high-temperature and high-pressure water. The decrease in the potential barrier arises from the temperature and the pressure dependencies of the dielectric constant (epsilon) and the ion product (p K w) of water. Numerical analysis shows that the pressure dependence of epsilon is negligible in the temperature range of 20-300 degrees C, whereas the pressure dependence of p K w is significant at temperatures of T > 150 degrees C. The theory reveals that the pressure dependence of the rate of size increment in the hydrothermal regime results from the pressure dependence of p K w. An increase in pressure in the hydrothermal water enhances the ionization of water molecules which reduces the surface potential of the particles. This effect lowers the interparticle repulsive potential barrier, which accelerates aggregation of the particles.

Characterization of curved hair of Japanese women with reference to internal structures and amino acid composition.

The variation of hair curvature in Japanese women was quantitatively investigated and the structure of curved hair was characterized with transmission electron microscopy (TEM) and amino acid analysis. Two hundred and thirty Japanese women volunteers, aged from 10 to 70 years, were randomly selected. The evaluation of the volunteers' natural hair shape showed that 53% of Japanese women have straight hair, while the remaining 47% have curved hair (varying from a slightly wavy shape to a frizzy style). The average curl radius of the volunteers' hair was determined to be 4.4 +/- 2.3 cm, and ranged widely from 0.6 to 16 cm. The TEM observation of curved hair fiber revealed an inhomogenous internal structure between the outer and inner regions of the curved shape. In relation to the inhomogeneous structure of the curved hair, different amino acid composition of the hair keratin was observed between the outer and inner regions. Interestingly, these results of the TEM observation and the amino acid analysis are analogous to the difference between the ortho- and paracortical cells in wool fibers, suggesting the universal structure of curved mammalian hair.

Spontaneous formation of fractal structures on triglyceride surfaces with reference to their super water-repellent properties.

Alkylketene dimer (AKD), a kind of wax, has been known to form fractal surfaces spontaneously and show super water-repellency. Such formation of water-repellent and fractal surfaces was also found in this work for triglycerides. Since the crystal phase transitions of these waxes were well studied, we studied the formation of their fractal surfaces through contact angle measurements, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). From time-dependent contact angle measurements, it was found that the formation of super water-repellent surfaces with fractal structures occurred spontaneously also on the triglyceride surfaces at different temperatures. The freshly solidified triglyceride surfaces were almost transparent, and their initial contact angles of water were close to 110 degrees. The surfaces then became rough and clouded after being incubated for a certain time at a specified temperature. The super water-repellent surfaces were quite rough and showed fractal structures with the dimension of ca. 2.2 calculated from the scanning electron microscopic (SEM) images by the box-counting method. The phase transformation from a metastable state to a stable cystalline one after the solidification from the melt of triglycerides was clearly observed by DSC and XRD measurements. The fractal crystalline structures and the super water-repellency resulted from this phase transformation and the crystal growth. Ensuring the initial sample solidified into the metastable state and curing the surface at an appropriate temperature are key factors for the successful preparation of fractal triglyceride surfaces by the solidification method.

Supercritical ethanol--a fascinating dispersion medium for silica nanoparticles.

For the first time, the dispersion stability of silica nanoparticles has been investigated in high-temperature and high-pressure ethanol by measuring the hydrodynamic diffusion coefficient of the particles by means of dynamic light scattering. The silica nanoparticles remain stable in ethanol within a wide temperature range of 24-304 degrees C at 12.3 MPa, and they start to aggregate at T >or= 305 degrees C. Numerical analysis reveals that the net interparticle repulsive potential barrier decreases dramatically with increasing temperature due to the changes in the properties of the medium. We observed that particles remain highly stable in the nonpolar supercritical ethanol in the temperature regime 241-304 degrees C, where the DLVO potential barrier is only 5-2 k(B)T. The dispersion stability of silica nanoparticles at this low potential barrier in high-temperature and high-pressure ethanol, especially in the supercritical ethanol, is fascinating. The silica-ethanol system might be a unique and special example in the colloidal dispersions. Results suggest that silica nanoparticles may be used as a model colloid to investigate the colloidal transport phenomena in the supercritical ethanol.

Supercritical water: a fascinating medium for soft matter.

Properties of water change dramatically at high temperatures and high pressures near and/or above the critical point ( = 374 °C, = 22.1 MPa). The dielectric constant, for example, decreases from 78 at 25 °C and 0.1 MPa to 6 at the critical point, the value of which is comparable to that of 1-dodecanol. As fascinating characteristics of soft matter rely on unique properties of ambient liquid water, the change should have significant impacts on soft matter. However, our knowledge of soft matter under such extreme conditions is virtually nonexistent. In this article, properties of colloidal dispersions in water at high temperatures and high pressures are described. Implications of the findings for geological processes in deep-subsurface are also discussed.

Synthetic myelin figures immobilized in polymer gels.

Myelin-like instabilities usually form from the interface of amphiphilic lamellar phases and solvent, and resemble the neuron-like structures in nerve systems. However, these myelin structures are thermodynamically unstable. We herein present our first success in synthesizing stable myelin figures separated organized-polymerization. Myelin figures formed with a polymerizable nonionic surfactant have been immobilized in polymer gels. The results obtained from confocal laser scanning microscopy (CLSM), small angle X-ray scattering (SASX) and freeze fracture transmission electron microscopy (FF-TEM) clearly prove that the myelin structures have been well immobilized without any structural change. The immobilized myelin structures in polymer gels were kept for 6 months and no obvious change was observed in their structures and/or shapes. The success in stabilizing these unstable myelin structures provides some potential for applications, such as anisotropic gels, electrophoresis mediums for the separation of hydrophobic materials and so on.

Formation mechanism of fractal structures on wax surfaces with reference to their super -repellency.

Alkylketene dimer (AKD: a kind of wax) spontaneously forms a fractal structure and its surfaces show super water-repellency (the contact angle = 174°). However, the formation mechanism of the fractal surfaces of AKD is still unclear. In this work, surface structures, wettability and phase behaviors of various waxes have been investigated in order to understand the mechanism for spontaneous formation of super water-repellent fractal surfaces. We have found an empirical general rule without any exceptions at least for the wax samples tested. First, the wax must form a meta-stable crystalline phase when solidified from its melt. Then, the super water-repellent fractal surfaces form spontaneously during the phase transition from a meta-stable to a stable crystalline form. The tempering method also supported the above rule for the waxes showing the fractal structure formation on their surfaces.

Preparation and characterisation of nanofibrous cellulose plate as a new solid support for microbial culture.

Porous plates made of nanofibrous crystalline cellulose were prepared, and used as a solid support for microbial cultures. Representative mesophilic microorganisms (, , and ) grew on the cellulose plate, just as well as they did on the conventional agar plate. optical microscopic examination revealed that the cellulose plate remained unchanged up to 280 °C at a constant pressure of 25 MPa. Due to the structural stability at high temperatures, a representative thermophile, , was cultured successfully on the cellulose plate at 80 °C. Mouse fibroblast cells did not show significant adhesion or extension on the cellulose plate.

Super water-repellent poly(alkylpyrrole) films having environmental stability.

We present electrochemical synthesis of super water-repellent poly(alkylpyrrole) films which exhibit excellent environmental stability in terms of contact angle (>150 degrees ) for water. The poly(alkylpyrrole) films synthesized under an optimized electrochemical condition consisted of thousands of micro-scaled 'needles' which densely aligned by shoulder to shoulder. The surface of the aligned 'needles' was analyzed by a box-counting method, to be a fractal structure with a dimension of 2.18.

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.

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.

Dispersion stability of colloids in sub- and supercritical water.

Dispersion stability of colloids has been investigated in sub- and supercritical water by measuring the hydrodynamic diffusion coefficients of the particles by means of dynamic light scattering. It is interestingly found that coagulation of the colloids in sub- and supercritical water is a universal phenomenon irrespective of the material of the colloids. Highly charged colloids were found to be more stable in water against high temperature. Numerical analysis reveals that the stability of the colloids at elevated temperature and pressure is primarily governed by the temperature dependence of the dielectric constant of the medium. The effect of the temperature dependence of the ion product of water (pKw) was found to be very little. Surface charge density and Stern potential may change with respect to temperature due to the readjustment of the ion concentration in the diffuse layer through the enhanced ion product and reduced dielectric constant of water. These are the secondary causes of the particle coagulations in sub- and supercritical water.

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).

Cooking cellulose in hot and compressed water.

Crystalline-to-amorphous transformation of cellulose in water, just like that for starch upon cooking called gelatinisation, is revealed at 320 degrees C and 25 MPa.

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.

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.