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Title: Molecular dynamics simulation of diffusion and electrical conductivity in montmorillonite interlayers

In this study, the diffusion of water and ions in the interlayer region of smectite clay minerals represents a direct probe of the type and strength of clay–fluid interactions. Interlayer diffusion also represents an important link between molecular simulation and macroscopic experiments. Here we use molecular dynamics simulation to investigate trends in cation and water diffusion in montmorillonite interlayers, looking specifically at the effects of layer charge, interlayer cation and cation charge (sodium or calcium), water content, and temperature. For Na-montmorillonite, the largest increase in ion and water diffusion coefficients occurs between the one-layer and two-layer hydrates, corresponding to the transition from inner-sphere to outer-sphere surface complexes. Calculated activation energies for ion and water diffusion in Na-montmorillonite are similar to each other and to the water hydrogen bond energy, suggesting the breaking of water–water and water–clay hydrogen bonds as a likely mechanism for interlayer diffusion. A comparison of interlayer diffusion with that of bulk electrolyte solutions reveals a clear trend of decreasing diffusion coefficient with increasing electrolyte concentration, and in most cases the interlayer diffusion results are nearly coincident with the corresponding bulk solutions. Trends in electrical conductivities computed from the ion diffusion coefficients are also compared.
Authors:
 [1] ;  [1] ;  [2] ;  [2]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  2. BP America, Houston, TX (United States)
Publication Date:
OSTI Identifier:
1240099
Report Number(s):
SAND--2016-1151J
Journal ID: ISSN 1932-7447; 619208
Grant/Contract Number:
AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 120; Journal Issue: 3; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
WFO
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY