ISSN:
0001-1541
Keywords:
Chemistry
;
Chemical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
We Compare molecular dynamics and electron paramagnetic resonance spectroscopic experiments on very dilute solutions of nitroxide free radicals in nearcritical and supercritical ethane. The measurement of the effective local density of solvent in the cybotactic region of the probe solute shows that maxima in local density enhancements occur in both computer and spectroscopic experiments at about half of the critical density, well removed from the maximum in the solvent's isothermal compressibility.Remarkably, at the bulk density where the maximum enhancement occurs, we observed long-lived clusters in the vicinity of the solute molecule. Geometrically defined clusters persist for at least 100 picoseconds of simulated time. The persistence of these clusters is corroborated by the behavior of the solute diffusion coefficient, which shows fluctuating values over simulated time periods as long as 1.3 nanoseconds. We argue that fluctuations in the local solvent density about a solute molecule are not a long-ranged solvent critical effect. Rather, they represent a localized, short-ranged quasicritical phenomenon induced by the solute, which may be described in terms of a transition between weakly attractive and attractive behavior. We discuss the implications of time-varying microstructure for reactions in supercritical fluid media.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/aic.690390615
