title: Investigating the effect of the zwitterion/lactone equilibrium of rhodamine B on the cybotactic region of the acetonitrile/scCO2 cosolvent.
abstract: We investigated the effect of adding acetonitrile to supercritical carbon dioxide (scCO(2)) in the presence of rhodamine B. This spectroscopic investigation of the scCO(2)/acetonitrile, rhodamine B/scCO(2), and rhodamine B/acetonitrile interactions revealed that rhodamine B, which possesses a temperature dependent equilibrium between a zwitterionic form and a neutral form, had a strong affect on the cybotactic region. To confirm that this effect was only dependent upon the rhodamine B/acetonitrile interactions and not merely due to the bulk-phase behavior of the scCO(2), we measured the compressibility of the scCO(2)/acetonitrile mixture and found it to be independent of the acetonitrile concentration to less than approximately 0.047 mol fraction. We fit the compressibility data using the Peng-Robinson equation of state because it is most appropriate for fluids in the region between 1.72 and 12.45 MPa and between 313 and 333 K.
authors.affiliation: Department of Chemistry and Physics, University of Portland, 5000 N. Willamette Boulevard, Portland, Oregon 97203, USA.
authors.forename: Andreas
authors.initials: A
authors.lastname: Gahlmann
authors.forename: Kimberly D
authors.initials: KD
authors.lastname: Kester
authors.forename: Steven G
authors.initials: SG
authors.lastname: Mayer