Recent molecular dynamics (MD) simulations using the fully-flexible CLAYFF forcefield predicted pyrophyllite edge surface structures and nanoparticle morphology that agree with the observed morphology and with ab initio simulations of the edge surfaces. These MD simulations also have provided an explanation for disordered edge surface structures attributable to the chemistry of octahedral sheet Al. We now extend our atomistic simulations to 2:1 clay minerals whose layer charge is not zero.  Simulations of K-Muscovite (layer charge -1.0, with Al substituted in the tetrahedral sheet) and Na-Montmorillonite edge surface (layer charge -0.2, with Mg substituted in the octahedral sheet) were performed to explore edge surface structures predicted by CLAYFF.  The K-Muscovite simulations produced results over a broad pH range that were consistent with previous simulations of the pyrophyllite edge surface and cationic edge surface complexes.  Ab initio geometry optimizations of an increasingly hydrolyzed Al-Mg dimer and seven variants of a molecular mechanics model of Na-Montmorillonite were used to evaluate montmorillonite edge surface structures.  The accuracy of the predicted edge structures was directly correlated to the density of octahedral substitutions at the edge surface: edge surface bond chains with substitution densities greater than the layer charge failed to result in stable edge surface structures.

Effects of isomorphic substitution on the 2:1 clay mineral edge structure: Insights from atomistic simulations

248th National Meeting (2014)

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