| Abstract
| - We investigated the effect of adding acetonitrile to supercritical carbon dioxide (scCO2) in the presence ofrhodamine B. This spectroscopic investigation of the scCO2/acetonitrile, rhodamine B/scCO2, and rhodamineB/acetonitrile interactions revealed that rhodamine B, which possesses a temperature dependent equilibriumbetween a zwitterionic form and a neutral form, had a strong affect on the cybotactic region. To confirm thatthis effect was only dependent upon the rhodamine B/acetonitrile interactions and not merely due to thebulk-phase behavior of the scCO2, we measured the compressibility of the scCO2/acetonitrile mixture andfound it to be independent of the acetonitrile concentration to less than ∼0.047 mol fraction. We fit thecompressibility data using the Peng−Robinson equation of state because it is most appropriate for fluids inthe region between 1.72 and 12.45 MPa and between 313 and 333 K.
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