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High-quality single crystalline calcium fluoride (CaF2) has been of considerable practical concern as an optical lens to an excimer laser stepper in the deep-ultraviolet region due to its excellent transparency. Highly accurate thermophysical properties of molten CaF2are essential as input data for a numerical simulation of the crystal growth process. The density of molten CaF2has been successfully determined in the stable and undercooled liquid states (1600–1820 K) with an electrostatic levitator. The temperature dependence of the density of molten CaF2is given by $$\rho \hbox{/kg}\cdot \hbox{m}^{-3} = 3580-0.63T(\pm 1.6\% ).$$The coefficient of cubical expansion of molten CaF2has been determined to be $$\beta \hbox{/K}^{-\hbox{1}}=\frac{1}{5683-T}.$$High-quality single crystalline calcium fluoride (CaF2) has been of considerable practical concern as an optical lens to an excimer laser stepper in the deep-ultraviolet region due to its excellent transparency. Highly accurate thermophysical properties of molten CaF2are essential as input data for a numerical simulation of the crystal growth process. The density of molten CaF2has been successfully determined in the stable and undercooled liquid states (1600–1820 K) with an electrostatic levitator. The temperature dependence of the density of molten CaF2is given by $$\rho \hbox{/kg}\cdot \hbox{m}^{-3} = 3580-0.63T(\pm 1.6\% ).$$The coefficient of cubical expansion of molten CaF2has been determined to be $$\beta \hbox{/K}^{-\hbox{1}}=\frac{1}{5683-T}.$$

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. The reliability of the apparatus was confirmed by measuring the IFT of polystyrene (PS)/scCO2 and polypropylene (PP)/CO2 systems. The IFT of the poly(methyl methacrylate) (PMMA)/scCO2 system with and without myristic acid was also measured. The IFT decreased on addition of myristic acid. The magnitude of the IFT depression due to the myristic acid was comparable to that of PS/scCO2 systems with the block copolymer surfactant, PS-b-poly(fluorooctyl acrylate). The surface activity of the myristic acid was confirmed by the decrease of IFT.

The synthesis of a Pt- and Pd-nanoparticle-dispersed polyimide film as a precursor for the preparation of a metal-doped carbon molecular sieve (CMS) membrane for hydrogen separation has been performed. Impregnation of Pt(II) acetylacetonate and Pd(II) acetylacetonate dissolved in supercritical CO2 yielded Pt and Pd nanoparticles (diameters 12 and 5 nm, respectively) that were highly dispersed inside polyimide films under optimized conditions. The impregnation temperature and varieties of polyimide films strongly influenced the dispersion of the metal particles. The Pd-doped CMS membrane was successfully prepared from the polyimide and Pd(II) acetylacetonate composite. It showed good hydrogen separation performance.

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. The hybrid surfactant employed was sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate (FC6-HC4), and the single-tailed surfactant was perfluoropolyether ammonium carboxylate (PFPECOONH4, CF3CF2(CF2OCF(CF3))4COONH4). All of the fluorinated AOT analogue surfactants exhibited an excellent level of activity at the water/CO2 interface compared with other fluorinated surfactants and AOT. With a larger hydrocarbon chain number in the CO2-philic tails (i.e., from 0 to 2), the IFT of the AOT analogue surfactants was increased. The area occupied by one surfactant molecule at the water/CO2 interface, A, and the critical microemulsion concentration, cμc, were determined and used to examine the water-to-surfactant molar ratio within a reversed micelle, W0^c, of the surfactants. The surfactants that form W/scCO2 microemulsions with a large W0^c were found to lower the interfacial tension efficiently irrespective of increases in temperature. To achieve the most desirable W0^c, the surfactant needs not only a high CO2-philicity of the tails but also a high Krafft point, properties which induce a low hydrophilic/CO2-philic balance.

The effects of the structural factors of surfactants such as CO2-philic tail length and molecular structure on the formation of water-in-supercritical CO2 (W/scCO2) type microemulsions were examined at various temperatures and pressures for fluorinated Aerosol-OT (AOT) analogue surfactants, sodium bis(1H,1H,5H-octafluoropentyl)-2-sulfosuccinate (di-HCF4), sodium bis(1H,1H,7H-dodecafluoroheptyl)-2-sulfosuccinate (di-HCF6), 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). With the all surfactants, a transparent single phase of water, a surfactant, and scCO2 mixture, or a W/scCO2 microemulsion phase, was formed under certain conditions. With an increase in the water composition, the microemulsion phase became a turbid W/scCO2 macroemulsion phase or completely separated into two phases. On the other hand, when pressure (CO2 density) or temperature was increased, the macroemulsion phase turned into a microemulsion phase. At CO2 densities <0.85 g/cm³ and temperatures <65 °C, di-HCF4 was unable to form a microemulsion. With an increase in fluorocarbon chain length (n) of di-HCFn, a microemulsion with a higher water-to-surfactant molar ratio (W0^c, 8 for di-HCF6 and 12 for di-HCF8 at CO2 density 0.85 g/cm³ and 35 °C) was formed. This suggests that the water/scCO2 interfacial activity increases with an increase in fluorocarbon chain length, resulting in the formation of stable W/scCO2 microemulsion. The superior ability of 8FS(EO)2 to stabilize W/scCO2 microemulsion with W0^c = 32 was found to be lowered with a replacement of the terminal CF3− by HCF2− of the fluorocarbon chains and an addition of oxyethylene units between the CO2-philic fluorocarbon chains and the hydrophilic sulfosuccinate group.