Subcritical and supercritical carbon dioxide (CO2), as an alternative solvent, is one of the unique fluids playing an important role in the development of environmentally favorable technologies. It acts as not only a good solvent to dissolve many low molecular substances, but also a good plasticizing agent for polymeric materials. Plasticization is the underlying principle in various polymer processing technologies with high-pressure CO2, such as low-temperature molding, polymer foaming, impregnation and surface modification. The purpose of this article is to review recent advances in polymer processing using CO2 fluid.
In this article, recent advances in the fundamental high pressure research for the phase equilibria of mixtures containing liquid crystals were reviewed. The effect of pressure on the crystal-nematic and nematic-isotropic phase transition temperatures, TCN and TNI, was investigated for MBBA (n-(4-methoxybenzylidene)-4-n-butylaniline), EBBA(n-(4-ethoxybenzylidene)-4-n-butylaniline), and binary mixtures containing these components such as (MBBA+EBBA), and (MBBA, EBBA+ benzene, n-hexadecane) at temperatures from 263 to 363 K and pressures up to 200 MPa. The measurements of TCN and TNI were performed using a compact high-pressure optical vessel designed for direct visual observation with the aid of a video microscope, and a three-terminal cylindrical capacitor for dielectric study. The effects of pressure and admixing of a nematic and non-mesogenic second component on the phase transitions are discussed.
One of the new focuses of the biological science was genomic science during the 20th century. The new frontier for the 21st century is protein science. Fundamental thermodynamic and kinetic theories, especially volume changes and activation volumes, for the pressure denaturation of proteins are described. The recent studies of molecular structure of proteins utilizing high-pressure spectroscopes (FTIR, NMR, SAXS) and the MD computer simulation are reviewed.
Densities and viscosities of formamide (FA)-, N-methylformamide (NMF)-, andN, N-dimethylformamide (DMF)-water mixtures were measured at 25°C under high pressure up to 200 MPa. The isothermal compressibility of the FA-water system decreases monotonously with an increase in the FA content at each pressure, but those of NMF-and DMF-water systems show a minimum against the composition in the water-rich region. Although the excess viscosity of the FA-water system is negative in the whole composition range, those of NMF-and DMF-water systems are positive. Such trends become remarkable with an increase in pressure. These results are discussed in terms of the hydrogen bonding between water and amide molecules and the hydrophobic hydration.
Recent Raman studies on the pressure-induce amorphization of pure ice and ice in aqueous LiCl solution are reviewed. We investigated the change of in situ Raman spectra of ice Ih as functions of pressure and temperature. In this paper, I show the spectral evidence for the formation of strong hydrogen bonds in high-density amorphous ice (HDA) at high pressures and the close similarity in spectral features of relaxed HDA to that of supercooled water at high pressures and low temperatures. It is found that the ice phase in LiCl·12H2O also transforms to an amorphous phase at ∼520 MPa, as in the case of pressure-induced amorphization of pure ice Ih to the HDA. The spectral changes with temperature show the possible existence of a transition from the relaxed amorphous phase to the supercooled liquid at high pressures and low temperatures.
In this article, recent advances in the fundamental research in the protein crystallization under high pressure were reviewed. Pressure is expected to be an important parameter to control protein crystallization, since hydrostatic pressure affects the whole system uniformly and can be changed very rapidly. So far, a lot of studies of protein crystallization under high pressure have been done, some less systematic than others. We have particularly focused on fundamental aspects (the solubility and the crystal growth kinetics) of protein crystallization under high pressure. The studies reviewed contribute significantly to high-pressure crystallography and high-pressure protein science.
In this article, the partial molar volumes of hydrophobic compounds in water were reviewed. The partial molar volume of ethylbenzene in water was drawn as a function of pressure, 0.10-400 MPa, and temperature, 273-323 K. Negative compressibility of the partial molar volume was observed in a low temperature and low pressure region. It suggested that the hydration water was less compressibile than bulk water. Aromatic ring which was included in naphthalene, anthracene, etc. showed different volumetric properties from alkylbenzenes and methylene group. The difference was discussed in a stand point of hydrophobic hydration.
Recent progress in the research in low-temperature liquid water and amorphous ices is reviewed. Polyamorphism in water is described as the key to understanding the puzzling properties of cold water. Polyamorphism is applied to other liquids under pressure and plays an important role in the study of liquids in general.
Original experimental values on the thermodynamic and thermophysical properties of pure and mixed fluids are reported in the world's journals. The large-scale databases, which compile these primary data are being developed, for example, by TRC/NIST (USA) and DECHEMA (Germany), provide printed collections of data tables and/or on-line access. Our working group has designed a database focused on the state behavior organic liquids (pressure-volume-temperature; PVT relationship, volumetric coefficients, speed of sound). The nearly ten years lasting project resulted in the compilation and evaluation of published experimental PVT data of pure organic liquids. The results for 315 substances are reviewed in the Journal of Chemical and Engineering Data.
Skutterudite compounds have recently attracted much attention from the viewpoint of both their potential as improved thermoelectric materials and their variety of electrical and magnetic properties, including exotic superconductivity, quadrupole ordering and anomalous metal-insulator transition. High-pressure synthesis is a powerful technique to prepare skutterudite compounds. In this article, the high-pressure synthesis of skutterudite compounds and their physical properties are reviewed.