Abstract
Experiments show that at 298 K and 1 atm pressure, the transfer free energy, μex, of water from its vapor to liquid normal alkanes CnH2n+2 (n=5...12) is negative. Earlier it was found that with the united-atom TraPPE model for alkanes and the SPC/E model for water, one had to artificially enhance the attractive alkane-water cross interaction to capture this behavior. Here we revisit the calculation of μex using the polarizable AMOEBA and the non-polarizable Charmm General (CGenFF) forcefields. We test both the AMOEBA03 and AMOEBA14 water models; the former has been validated with the AMOEBA alkane model while the latter is a revision of AMOEBA03 to better describe liquid water. We calculate μex using the test particle method. With CGenFF, μex is positive and the error relative to experiments is about 1.5 kBT. With AMOEBA, μex is negative and deviations relative to experiments are between 0.25 kBT (AMOEBA14) and 0.5 kBT (AMOEBA03). Quantum chemical calculations in a continuum solvent suggest that zero point effects may account for some of the deviation. Forcefield limitations notwithstanding, electrostatic and induction effects, commonly ignored in consideration of water-alkane interactions, appear to be decisive in the solubility of water in alkanes.
| Original language | English |
|---|---|
| Article number | 074506 |
| Journal | Journal of Chemical Physics |
| Volume | 147 |
| Issue number | 7 |
| DOIs | |
| State | Published - Aug 21 2017 |
| Externally published | Yes |
Funding
D.A., A.V.P., W.G.C. are grateful for the financial support from the Robert A. Welch Foundation (Grant No. C-1241), the Rice University Consortium for Processes in Porous Media (Houston, TX, USA), and the Abu Dhabi National Oil Company (ADNOC). D.B. was supported by the Division of Material Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. W-7405-430 ENG-82 with Iowa State University. We thank B. Xue, D. B. Harwood, and J. I. Siepmann for their comments on Ref. 7 that led us to correct that work8 and focus on the vapor-to-liquid transfer process. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
| Funders | Funder number |
|---|---|
| D.A. | |
| U.S. Department of Energy | W-7405-430, 7, W-7405-430 ENG-82 |
| Welch Foundation | C-1241 |
| Office of Science | DE-AC02-05CH11231 |
| Basic Energy Sciences | |
| Advanced Scientific Computing Research | |
| Rice University | |
| Iowa State University | work8 |
| Center for Environmental Sciences and Engineering | |
| Robert A. and Renee E. Belfer Family Foundation | |
| Apple University Development Fund, Apple University Consortium | |
| Abu Dhabi National Oil Company |