Phase Behavior of a Carbon Dioxide/Methyl Trimethoxy Silane/Polystyrene Ternary System.

Recently, polymeric foams filled with a silica aerogel have been developed. The phase behavior of CO₂/silicon alkoxide binary systems and CO₂/silicon alkoxide/polymer ternary systems is an important factor that affects the design of novel processes. The phase behavior of a carbon dioxide (CO₂)/methyl trimethoxy silane (MTMS)/polystyrene (PS) ternary system was measured using a synthetic method involving the observation of the bubble and cloud point.

Formation of Nanofibrous Structure in Biopolymer Aerogel during Supercritical CO Processing: The Case of Chitosan Aerogel.

Supercritical drying is widely considered as the gold standard to produce aerogels that preserve the microstructure of the gels, but we have found this is not always the case. Chitosan aerogel, one of the emerging biopolymer aerogels, was prepared by chemical cross-linking gelation, followed by solvent exchange with methanol and supercritical drying using CO. Small-angle X-ray scattering analysis shows that the structure of the wet gel, which consists of Gaussian chains of individual molecular strands, converts into a nanofibrous network during CO processing.

Novel Orally Disintegrating Tablets Produced Using a High-Pressure Carbon Dioxides Process.

It is well known that high-pressure carbon dioxide (CO) lowers the glass transition temperature (T) of polymers. We therefore investigated whether T depression of high-pressure CO results in interparticle bridging of a polymer and the tablet characteristics that makes the manufacture of an orally disintegrating tablet (ODT) possible. Copolyvidone (Kollidon) and polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (Soluplus) were examined and found to exhibit a large T depression.

Aldehyde Approach to Hydrophobic Modification of Chitosan Aerogels.

Biobased nanofiber aerogels are ones of the attractive emerging materials in the fields of biochemistry and materials chemistry, but their poor humidity stability due to high hydrophilicity has limited their practical uses. In this paper, a new series of hydrophobic nanofibrous aerogels made from regenerated chitosan and alkyl aldehydes were prepared via a simple one-pot reaction followed by supercritical drying. Hexanal-modified chitosan aerogel shows excellent hydrophobicity with a water contact angle of ∼136°, a low density of 0.

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.

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.

Characterization of water/supercritical CO2 microemulsion by UV-visible spectroscopy and dynamic light scattering.

A water/supercritical CO(2) microemulsion (W/scCO(2) microE) with methyl orange (MO) and sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate, 8FS(EO)(2), was characterized by means of UV-visible absorption spectral and dynamic light scattering (DLS) measurements. Visual observation of the scCO(2) mixtures revealed transparent and reddish scCO(2) phases with and without separated excess water; they were identified as Winsor-II and Winsor-IV W/scCO(2) microE, respectively. The polarities of the aqueous cores in the Winsor-IV W/scCO(2) microE were examined by observing the spectral shift of the absorbance maximum of MO.

Preparation and properties of liposomes composed of various phospholipids with different hydrophobic chains using a supercritical reverse phase evaporation method.

Liposomes were prepared by the supercritical reverse phase evaporation method developed in our laboratory using various phospholipids with different hydrocarbon chains. The effects of the length of alkyl chain and number of unsaturated bonds of phospholipids on the properties of liposomal membranes were examined through trapping efficiency measurements, transmission electron microscopic observations, and osmotic response measurements. The trapping efficiency for water-soluble drugs of liposomes prepared by our method was greatly higher than that of liposomes prepared by the conventional Bangham method.

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.

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.

Optimum tail length of fluorinated double-tail anionic surfactant for water/supercritical CO2 microemulsion formation.

The effect of surfactant tail structure on the stability of a water/supercritical CO2 microemulsion (W/scCO2 muE) was examined for various fluorinated double-tail anionic surfactants of different fluorocarbon chain lengths, F(CF2)n (n = 4, 6, 8, and 10), and oxyethylene spacer lengths, (CH2CH2O)(m/2) (m = 2 and 4). The phase behavior of the water/surfactant/CO2 systems was studied over a wide range of CO2 densities from 0.70 to 0.

Surfactant-mixing effects on the interfacial tension and the microemulsion formation in water/supercritical CO2 system.

The effects of surfactant mixing on interfacial tension and on microemulsion formation were examined for systems of air/water and water/supercritical CO2 (scCO2) interfaces and for water/scCO2 microemulsions. A fluorinated surfactant, sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO)2), was mixed with the three hydrocarbon surfactants, Pluronic L31, Tergitol TMN-6, and decyltrimethylammonium chloride (DeTAC), at equimolar ratio. For all the cases, the interfacial tension was significantly lowered by the mixing.

One-step preparation of chitosan-coated cationic liposomes by an improved supercritical reverse-phase evaporation method.

High-pressure carbon dioxide in contact with water dissolves to form carbonic acid, causing a decrease in pH. By use of these characteristics of a CO2/H2O biphasic system, chitosan-coated cationic liposomes of l-alpha-dipalmitoylphosphatidylcholine were successfully prepared by an improved supercritical reverse-phase evaporation (ISCRPE) method. Liposome-chitosan complexes carrying a positive charge were prepared in a single-step procedure without the use of acid or organic solvent, including ethanol.

Preparation of liposomes using an improved supercritical reverse phase evaporation method.

Liposomes of various phospholipids were prepared using an improved supercritical reverse phase evaporation (ISCRPE) method that utilizes supercritical carbon dioxide (scCO(2)) as an alternative to organic solvents. Using this method, in the absence of any organic solvent including ethanol, the maximum trapping efficiency of glucose reached 36% for 20 mM l-alpha-dioleoylphosphatidylcholine (DOPC), compared to less than 10% using the Bangham method. Liposomes prepared by the ISCRPE method were highly stable for one month at room temperature.

Electrochemical synthesis of a polypyrrole thin film with supercritical carbon dioxide as a solvent.

A conductive polypyrrole (PPy) film was successfully synthesized in a homogeneous supercritical carbon dioxide (scCO2)/acetonitrile (AN) system. The occurrence of a homogeneous supercritical state was confirmed by observations of the phase behavior of the system through a high-pressure cell with a viewing window. The concentration of a supporting electrolyte, tetrabutylammonium hexafluorophosphate (TBAPF6), significantly changed the phase behavior of the scCO2/AN system.

Noncatalytic mono-N-methylation of aniline in supercritical methanol: the kinetics and acid/base effect.

Aniline is easily N-methylated in supercritical methanol without catalyst at 350 degrees C and 0.237 g cm-3 to give mono-N-methylaniline with high selectivity, and the reaction rate is increased by a small amount of base (LiOH, NaOH, KOH, and CH3ONa), indicating a difference in the reaction mechanism from the ordinary acid-catalyzed one.

Interfacial properties of branch-tailed fluorinated surfactants yielding a water/supercritical CO2 microemulsion.

We have examined the interfacial properties of several fluorinated surfactants in a water/CO2 mixture with a pendant drop tensiometer and revealed the relationships between the interfacial properties, the surfactant structure, and the microemulsifying power. We employed the following Aerosol-OT analogue surfactants that have two fluorinated tails: bis(1H,1H,5H-octafluoropentyl)-2-sulfosuccinate (di-HCF4), sodium bis(1H,1H,9H-hexadecafluorononyl)-2-sulfosuccinate (di-HCF8), sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO)2), and sodium bis((1H,1H,2H,2H-heptadecafluorodecyl)-oxyethylene)-2-sulfosuccinate (8FS(EO)4). To discuss the effect of the fluorocarbon/hydrocarbon ratio in single surfactant molecules, water/CO2 interfacial tension (IFT) of a hybrid surfactant with one fluorocarbon and one hydrocarbon tail, that of a surfactant with a single fluorinated tail, and that of a hydrocarbon surfactant, Aerosol-OT (AOT), were examined.

Acetone hydration in supercritical water: (13)C-NMR spectroscopy and Monte Carlo simulation.

The (13)C-NMR chemical shift of acetone delta((13)C[Double Bond]O) was measured in aqueous solution at high temperatures up to 400 degrees C and water densities of 0.10-0.60 g/cm(3) for the study of hydration structure in the supercritical conditions.

Surface activity of myristic acid in the poly(methyl methacrylate)/supercritical carbon dioxide system.

To confirm the surface activity of myristic acid in the dispersion polymerization of vinyl monomers in scCO2, the interfacial tension (IFT) at the polymer/supercritical carbon dioxide (scCO2) interface has been measured. For the IFT measurements, a high-pressure pendant drop apparatus was constructed. The IFT data was obtained by the axisymmetric drop shape analysis of melt polymer droplets formed at the tip of a capillary.

TiO2-montmorillonite composites via supercritical intercalation.

The successful preparation of TiO2-montmorillonite mesoporous composites using intercalation of titanium isopropoxide dissolved in supercritical carbon dioxide involved ion exchange of interlayer cations by hydrophobic cations.