title: Liquid Structure of CO2-Reactive Aprotic Heterocyclic Anion Ionic Liquids from X-ray Scattering and Molecular Dynamics.
abstract: A combination of X-ray scattering experiments and molecular dynamics simulations were conducted to investigate the structure of ionic liquids (ILs) which chemically bind CO2. The structure functions were measured and computed for four different ILs consisting of two different phosphonium cations, triethyloctylphosphonium ([P2228]+) and trihexyltetradecylphosphonium ([P66614]+), paired with two different aprotic heterocyclic anions which chemically react with CO2, 2-cyanopyrrolide, and 1,2,4-triazolide. Simulations were able to reproduce the experimental structure functions, and by deconstructing the simulated structure functions, further information on the liquid structure was obtained. All structure functions of the ILs studied had three primary features which have been seen before in other ILs: a prepeak near 0.3-0.4 Å-1corresponding to polar/nonpolar domain alternation, a charge alternation peak near 0.8 Å-1, and a peak near 1.5 Å-1due to interactions of adjacent molecules. The liquid structure functions were only mildly sensitive to the specific anion and whether or not they were reacted with CO2. Upon reacting with CO2, small changes were observed in the structure functions of the [P2228]+ILs, whereas virtually no change was observed upon reacting with CO2in the corresponding [P66614]+ILs. When the [P2228]+cation was replaced with the [P66614]+cation, there was a significant increase in the intensities of the prepeak and adjacency interaction peak. While many of the liquid structure functions are similar, the actual liquid structures differ as demonstrated by computed spatial distribution functions.
authors: Department of Chemical and Biomolecular Engineering University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors: Quintin R
authors: QR
authors: Sheridan
authors: Department of Chemical and Biomolecular Engineering University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors: Seungmin
authors: S
authors: Oh
authors: Department of Chemical and Biomolecular Engineering University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors: Oscar
authors: O
authors: Morales-Collazo
authors: Department of Chemistry and Chemical Biology Rutgers, The State University of New Jersey , Piscataway, New Jersey 08854, United States.
authors: Edward W
authors: EW
authors: Castner
authors: Department of Chemical and Biomolecular Engineering University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors: Joan F
authors: JF
authors: Brennecke
authors: Department of Chemical and Biomolecular Engineering University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors: Edward J
authors: EJ
authors: Maginn