UV-visible spectra of organic probes are reported in supercritical water (SCW) for the first time up to 440 degrees C and 5000 psia. Solvatochromic shifts in the pi-pi* absorbance band of benzophenone are compared with those of the n-pi* band of acetone to characterize the dipolarity, polarizability, and hydrogen bond donor strength of water. In the near-critical region (0.5 < rho(r) < 1.5), physical and hydrogen-bonding interactions augment the density of water about each probe, relative to the bulk density. At 380 OC, hydrogen bonding persists at a density of only 0.1 g/mL but rapidly disappears at lower densities. Spectroscopic measurements of interactions between SCW and organic solutes at the molecular level provide new insights into solvent effects on chemical reactions in SCW.
E. M. Taleff, Henshall, G. A., Lesuer, D. R., and Nieh, T. G., “Warm Formability of Aluminum-Magnesium Alloys,” in Aluminum Alloys: Their Physical Properties and Mechanical Properties (ICAA4), Atlanta, Georgia: Georgia Institute of Technology, 1994, pp. 338–345.Abstract
A one-phase microemulsion composed of a hybrid fluorocarbon/hydrocarbon surfactant C7F15CH(OS0(3)(-)- Na+)C7H15, water, and CO2 solubilizes substantial amounts of water. For example, the water-to-surfactant ratio in a single phase microemulsion is as high as 32 at 25 degrees C and 231 bar, compared with a value near 0 for more than 150 previously studied surfactants for temperatures up to 50 degrees C. Also with 1.9 wt % surfactant, up to 2 wt % water is soluble, which is 10 times the amount soluble in pure CO2. The requirements for the design of surfactants that form microemulsions in CO2 are examined.
The phase equilibria distribution of naphthalene between CO2, water, and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer micelle phases is examined experimentally and predicted semiquantitatively using a molecular thermodynamic model. The predictions treat the poly(propyleneoxide) micelle core as a ’’pseudophase’’ resembling an ether. The favorable distribution coefficients at pressures as low as 70 bar suggest that CO2 is appropriate for regenerating block copolymer micelles used for concentration of trace organics in dilute aqueous solutions.