The wide use of clay minerals in industrial applications (catalysis, formulation), energy and ecological engineering (oil recovery, ground water remediation, geological barrier for radioactive waste and CO2) is partly due to their remarkable properties of retention at the mineral surface. In environmental engineering, the role of water on clay permeability and retention properties is crucial. Indeed, the water is the vector of the motion of the species present in the medium, hazardous elements for instance.Clays can show different behaviors towards water, depending in particular on the value of the negative structural charge carried by the mineral layers: although hydrophobic when uncharged, a clay can become hydrophilic when charged. This is partly due to the favorable hydration of the counter-ions located between the layers, which causes the swelling of the clay nanopores.Simulations at the atomic level can help because they allow a detailed picture of the structure, thermodynamics and dynamics of the fluid at the interface. They are already used to explain the hydrophobic/hydrophilic property of various clays such as : Talc, Pyrophyllite and Montmorillonite[1,2]. Unfortunately, the numerical results do not always reproduce quantitatively the experimental results, which casts, consequently, a doubt on the validity of simulations interpretations[3]. In particular, the polarizability is not taken into account although it can play a significant role especially when an electric field is present at the interface[4].This is why the PHENIX laboratory is developing a polarizable force field to study clay/water systems from DFT calculations. The force-fields determined for neutral and charged clay (Pyrophyllite, Talc, Montmorillonite, and Hectorite) are shown to well reproduce the available experimental data and are very promising.Figure : Left : The Pyrophyllite structure ; Right : The experimental and theoritical Pryrophyllite spectrum[1] B.Rotenberg, A.J. Patel, D. Chandler, Molecular explanation for why talc surfaces can be both hydrophilic and hydrophobic, J. Am. Chem. Soc., 2011 , 133, 20521.[2] A.Botan, V.Marry, B.Rotenberg, P.Turq, B.Noetinger, How electrostatics influences hydrodynamic boundary conditions: Poiseuille and electro-osmotic flows in clay nanopores, J. Phys. Chem. C., 2013 , 117, 978-985.[3] Marry, V., Dubois, E., Malikova, N., Breu, J., Haussler, W., 2013. Anisotropy of water dynamics in clays: insights from molecular simulations for experimental QENS analysis. J. Phys. Chem. C, 2013 , 117, 15106 - 15115.[4] Ganesh Kamath et al, Comparison of select polarizable and non-polarizable water models in predicting solvation dynamics of water confined between MgO slabs, J. Phys.: Condens. Matter 2013 , 25 305003 doi:10.1088/0953-8984/25/30/305003

Development of a polarizable forces field for clays

248th National Meeting (2014)

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