(193d) Structure and Dynamics of Energy-Relevant Fluid-Solid Interfaces: A Long Journey with Peter Cummings through Very Small Times and Places!

My interactions with Peter Cummings began in 1994 when he became a joint ORNL/University of Tennessee (Knoxville) Distinguished Scientist, and later joint Chief Scientist of ORNL’s Center for Nanophase Materials Science and Professor of Chemical Engineering at Vanderbilt University.  In this talk I will review the development and ongoing application of our integrated molecular dynamics simulations and neutron/X-ray scattering studies of bulk aqueous and room temperature ionic liquid electrolytes and the changes in their structure and dynamics in the nanoscale region at neutral and charged surfaces (minerals, electrodes, etc.), including the effects of nanoconfinement.

Peter’s collaboration with our Aqueous Chemistry and Geochemistry program began even before he joined ORNL, with quantitative experiments and modeling of the thermodynamic properties and phase equilibria of high temperature water and aqueous solutions into the supercritical regime¹. This work applied the SPC water model, which could be readily adapted to simulate dissolved inorganic salts.  This collaboration lead to the development of the Gaussian Charge Polarizable (GPC) force field for water², which is shown to be more accurate in describing the structure and phase envelope of pure water over very wide ranges of temperature and density³.  My research group is now adapting GPC for aqueous electrolytes, and further demonstrates the excellent agreement between GPC and the most recent X-ray scattering data^4,5. 

            Over the last 14 years Peter has been a co-PI in our project funded by DOE’s Office of Basic Energy Sciences, Geoscience Research Program, with the current name “Geochemical Equilibria and Reaction Dynamics”, in which we seek to quantify the atomic-molecular origins of geochemical processes associated with fluid-rock interactions that control contaminant transport, nuclear waste isolation, fossil and geothermal energy exploitation, and the evolution of porosity/permeability in the subsurface.  This work has broad applications in other areas of science, such as catalyst and nanomaterials synthesis and stability^6,7.  Since 2009, Peter has been a Thrust Leader, and is now the Deputy Director of the Fluid Interface Reactions, Structures and Transport (FIRST Center), of which I am the Director, which is supported by DOE’s Office of Science, Office of Basic Energy Sciences.  In this project, we have applied molecular modeling and X-ray/neutron scattering approaches to room temperature ionic liquid interactions with carbon electrode materials in planar, curved and nanopore-confined geometries^8,9.

¹Cummings, P.T.; Cochran, H.D., Simonson, J.M., Mesmer, R.E., Karaboni, S. J. Chem. Phys., 94:5606 (1991).

²Chialvo, A.A.; Cummings, P.T. Fluid Phase Equil., 150:73 (1998).

³Paricaud, P., Predota, M., Chialvo, A.A., Cummings, P.T. J. Chem. Phys., 122:244511 (2005).

⁴Chialvo, A.A., Vlcek, L. J. Phys. Chem. B (in review).

⁵Skinner, L.B.; Huang, C.; Schlesinger, D.; Pettersson, L.G.M.; Nilsson, A.; Benmore, C.J. J. Chem. Phys., 138:074506 (2013).

⁶Wesolowski, D.J., et al., Phys. Rev. B 85:167401 (2012).

⁷Wang, H.-W.; Wesolowski, D.J., et al. J. Amer. Chem. Soc. 135:6885 (2013).

⁸Feng, G.; Li, S.; Presser, V.; Cummings, P.T. J. Phys. Chem. Lett., 4:3367 (2013).

⁹Banuelos, J.L., et al. Chem. Mater., 26:1144 (2014).