Solvent Density Inhomogeneities in Supercritical CO 2 by Pyrene Probe

Abstract

In recent years supercritical CO 2 (SC CO 2) has been widely used in environmental earth sciences and the solvating properties of SC CO 2 in the compressible region play a very important role in applications. In this supercritical region the fluid density may vary dramatically with modest changes in temperature and pressure. Understanding the unusual solvation behavior of SC CO 2 by the efficient probe molecular is very critical to the theory and application of supercritical science and technology. A new view is represented in this article on the technique by fluorescence probe pyrene in SC CO 2 at 308.15 K and different pressures. The order parameter methods and the new concept of the solvent effect have been introduced in proposed mode approach of the reference point, different from the traditional method by reference line, to estimate the local density enhancement change for SC CO 2 near the critical region. Three-density region model, solvent density inhomogeneities and intermolecular interactions of probe pyrene in SC CO 2 are also discussed. Combining the local density enhancements by the fluorescence indicator method and isothermal compressibility by the thermodynamic measurement, we can better understand the unusual behavior of SC CO 2 from microscopic and macroscopic views.