Katsuto Otake

A new model for the thermally induced volume phase transition of gels

A theoretical model that considers hydrophobic interaction is proposed for the thermally induced discontinuous shrinkage of hydrogels. In this model, the free energy of a hydrogel is divided into four parts: the elastic free energy of networks formulated according to the theory which takes the limit of elongation into account, the free energy arising from osmotic pressure of dissociated counterions in the gel, the free energy of interactions except for the hydrophobic interaction represented by a virial‐type volume interaction equation, and the free energy of the hydrophobic interaction. By the former three terms, the thermally induced swelling of gels and the effects of aspect ratio of segment are expressed. The incorporation of the fourth hydrophobic interaction term makes it possible to explain the thermally induced shrinkage of gels, and suggests the possibility of an explanation of ‘‘convexo’’‐type volume phase transition by means of the hydrophobic interaction.

Water/Supercritical CO2 Microemulsions with Mixed Surfactant Systems

Phase behavior was investigated for water/supercritical CO 2 (W/scCO2) microemulsions stabilized with sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO) 2) mixed with various guest surfactants. Only for the mixtures with fluorocarbon-hydrocarbon hybrid anionic surfactants (FC6-HC n), the maximum water-to-surfactant molar ratio (W0(c)) was larger than that estimated from linear interpolation of the W0(c) values for pure 8FS(EO) 2 and pure guest surfactant. Fourier transform infrared (FT-IR) measurement for the microemulsion revealed that the mixing of 8FS(EO) 2 with FC6-HC n can prevent a phase transition from the microemulsion to the liquid crystal even in the presence of excess water. It was also found from the measurement of water/scCO 2 interfacial tension that the area occupied per surfactant molecule was markedly increased by the mixing with FC6-HC n. The loose molecular packing, probably due to a microsegregation of 8FS(EO) 2 and FC6-HC n, is consistent with the enhanced stability of the microemulsion upon surfactant mixing.

High pressure vapor-liquid and vapor-liquid-liquid equilibria for systems containing supercritical carbon dioxide, water and furfural

Abstract We measured vapor-liquid equilibrium for a binary system CO2furfural at temperatures of 303 and 323 K and vapor-liquid-liquid equilibrium for a ternary system CO2waterfurfural at temperatures of 303, 323 and 343 K and pressure of 5 MPa to obtain fundamental data for concentration of furfural by using three phase separation technique. Furthermore the experimental data were compared with results calculated by the Peng-Robinson equation of state combined with an asymmetric mixing rule. Results indicated that (1) the furfural-rich liquid phase contained more than 90wt% furfural on CO2-free basis and its concentration increased with decrease in temperature, and (2) the Peng-Robinson equation correlated the binary vapor-liquid equilibrium satisfactorily and estimated the ternary vapor-liquid-liquid equilibrium fairly well.

Solubility and adsorption of high pressure carbon dioxide to poly(styrene)

Abstract Solubility and adsorption of high pressure carbon dioxide (CO2) to poly(styrene) (PS) were measured at 313.2 K and pressures up to 17 MPa using a quartz crystal microbalance (QCM) as a detector. Two kinds of PS film, made by dip coating (d-PS) and plasma polymerization (p-PS), were used as samples. The amount of adsorption onto both films was almost the same within the experimental range. The solubility to both films increased almost linearly against activity of CO2 up to unity, and that to p-PS was slightly higher than that to d-PS. Above unity, the solubility to p-PS film increased with the increase in activity. In contrast, solubility to d-PS sharply decreased near the unity and became a constant value.

Fourier transform infrared spectroscopic study of water-in-supercritical CO2 microemulsion as a function of water content.

Fourier transform infrared (FT-IR) spectrum of water-in-supercritical CO(2) microemulsion was measured at 60 degrees C and 30.0 MPa over a wide range of water/CO(2) ratio from 0.0 to 1.2 wt % to study the distribution of water into CO(2), interfacial area around surfactant headgroup, and core water pool. The microemulsion was stabilized by sodium bis(1H,1H,2H, 2H-heptadecafluorodecyl)-2-sulfosuccinate [8FS(EO)(2)] equimolarly mixed with sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate [FC6HC4] or with poly(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether [TMN-6]. The signal area of the O-H stretching band of water suggested that the number of water molecules in the microemulsion increases linearly with the water/CO(2) ratio, except for a slow initial increase below 0.4 wt % due to a part of water dissolved in CO(2). The amount of water in CO(2) was evaluated by decomposing the bending band of water into two components, one at lower frequency ascribed to water in CO(2) and the other at higher frequency to water in the microemulsion. The decomposition confirmed that CO(2) is saturated with water at the water content of 0.4 wt %. It was also revealed, from the symmetric SO stretching frequency of the surfactant, that the sulfonate headgroup is completely hydrated at the water/CO(2) ratio of 0.4-0.5 wt %. The results demonstrated that water is introduced preferentially into CO(2) and the interfacial area at small water content, and then is loaded into the micelle core after the saturation of CO(2) with water and the full hydration of the surfactant headgroup.

Microscopic solvent structure of subcritical and supercritical methanol from ultraviolet/visible absorption and fluorescence spectroscopies

Ultraviolet/visible absorption and fluorescence spectroscopies at different temperatures and pressures were applied to investigate the microscopic solvent structures of subcritical and supercritical methanol using 4-nitroanisole, ethyl-(4-dimethylamino)benzoate, Reichardt’s dye, and anthracene as the probe molecules. It was found that at temperatures higher than 150 °C the long winding chains of sequentially hydrogen-bonded methanol molecules were probably broken, but the small hydrogen-bonded aggregates possibly existed in methanol even at higher temperature. It was also found that the solvation process of the anthracene molecule in the S0-ground state obeyed the Langmuir adsorption model. However, in the case of fluorescence measurements in supercritical methanol, we detected deviations from the simple Langmuir adsorption model. These deviations were explained in terms of preferential solvation of the solvent molecules around photoexcited anthracene. Judging from the experimental results, it was conclud...

Comparison of ultrasonic degradation rates constants of methylene blue at 22.8 kHz, 127 kHz, and 490 kHz

Techniques such as solvent extraction, incineration, chemical dehalogenation, and biodegradation have been investigated for the degradation of hazardous organic compounds. We found ultrasound to be an attractive technology for the degradation of hazardous organic compounds in water. However, the effects of ultrasonic frequency on degradation rate constants were not investigated quantitatively. In this study, the degradation process of a model for hazardous organic compound methylene blue was investigated using ultrasonic irradiation. The study focused on the effects of ultrasonic frequency and ultrasonic power on the degradation rate constant. The apparent degradation rate constants were estimated based on time dependence of methylene blue concentration assuming pseudo-first-order kinetics for the decomposition. A linear relationship between the apparent degradation rate constant and ultrasonic power was identified. In addition, the apparent degradation rate constants at frequencies of 127 and 490 kHz were much larger than those at 22.8 kHz. A relationship between the apparent degradation rate constant and the sonochemical efficiency value (SE value) was also found. Based on these results, a simple model for estimating the apparent degradation rate constant of methylene blue based on the ultrasonic power and the SE value is proposed in this study.

Microscopic solvent structure of supercritical carbon dioxide and its mixtures with methanol in the cybotactic region of the solute molecule

UV/VIS absorption spectroscopy was used to estimate the microscopic solvent polarities of supercritical carbon dioxide alone and its mixtures with methanol. It was found that the local composition of methanol in the cybotactic region of 4-nitroanisole was larger than the corresponding bulk concentration. With increasing pressure the methanol molecules were pressed out of the solvation shell of 4-nitroanisole by the carbon dioxide molecules. From the solubility measurements the solvation numbers of the carbon dioxide molecules around 4-nitroanisole were calculated as a function of fluid density.

Frequency change of a quartz crystal microbalance at the supercritical condition of carbon dioxide

Abstract The frequency change of a quartz crystal microbalance was examined at 40 °C and pressures up to 15 MPa with He, N2, and C02 as a pressurizing medium. The frequency largely decreased near the critical point of the C02. The change was caused by the rapid increase of the weight of C02 physically adsorbed on the evaporated silver electrodes surface.

Kinetics analysis for development of a rate constant estimation model for ultrasonic degradation reaction of methylene blue

Ultrasound has been used as an advanced oxidation method for wastewater treatment. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effect of ultrasonic frequency on degradation rate has not been investigated. In our previous study, a simple model for estimating the apparent degradation rate of methylene blue was proposed. In this study, sonochemical degradation of methylene blue was performed at various frequencies. Apparent degradation rate constant was evaluated assuming that sonochemical degradation of methylene blue was a first-order reaction. Specifically, we focused on effects of ultrasonic frequency and power on rate constant, and the applicability of our proposed model was demonstrated. Using this approach, maximum sonochemical degradation rate was observed at 490 kHz, which agrees with a previous investigation into the effect of frequency on the sonochemical efficiency value evaluated by KI oxidation dosimetry. Degradation rate increased with ultrasonic power at every frequency. It was also observed that threshold power must be reached for the degradation reaction to progress. The initial methylene blue concentration and the apparent degradation rate constant have a relation of an inverse proportion. Our proposed model for estimating the apparent degradation rate constant using ultrasonic power and sonochemical efficiency value can apply to this study which extended the frequency and initial concentration range.