Mesoscale properties of clay aggregates from potential of mean force representation of interactions between nanoplatelets

Abstract

Face-to-face and edge-to-edge free energy interactions of Wyoming Na-montmorillonite platelets were studied by calculating potential of mean force along their center to center reaction coordinate using explicit solvent (i.e., water) molecular dynamics and free energy perturbation methods. Using a series of configurations, the Gay-Berne potential was parametrized and used to examine the meso-scale aggregation and properties of platelets that are initially random oriented under isothermal-isobaric condition.Aggregates of clay was defined by geometrical analysis of face-to-face proximity of platelets with size distribution described by a log-normal function. The isotropy of the microstructure was assessed by computing a scalar order parameter. The number of platelets per aggregate and anisotropy of the microstructure both increases with platelet plan area. System becomes more ordered and aggregate size increases with increasing pressure until maximum ordered state. Further increase of pressure slides platelets relative to each other leading to smaller aggregate size. The geometrical arrangement of aggregates affects mechanical properties of the system. The elastic properties of the meso-scale aggregate assembly are reported. It is found that the elastic properties at this scale are close to the cubic systems. The elastic stiffness and 1 anisotropy of the assembly increases with the size of the platelets and the level of external pressure.

The Potential of Mean Force concept for bridging (length and time) scales in the modeling of complex porous materials

“…The experimental tools applied to measure such quantities in cement were electron-microscopy imaging, nanoindentation tests, small angle X-rays and neutron scattering (SAXS and SANS), nuclear magnetic resonance (NMR) spectroscopy and adsorption desorption experiment of N 2 and water. A remarkable agreement with experiment was achieved for both cement and clays [2,7].…”

“…In this case, the molecular structures of the solvent and the surfaces have to be taken into account. Therefore, numerous works adopted a fullatomistic description of the system to study for instance the intralamellar swelling of smectite clays [7]. However, as mentioned above, the computational cost of these atomistic simulations is very significant preampting coarse-grained simulations.…”

“…The fit of the PMF for sodium Montmorillonite extracted from atomistic scale requires going beyond the Gay-Berne potential that can only describe a single well PMF. In the case of cement hydrate (CSH), extracting the PMF is more difficult as CSH is not a well defined compound with a weill defined chemistry but rather a non stoechimetric coumpound with a range of possible compositions Figure 2: Face-to-face PMF for Sodium-Montmorillonite clay at 300K [7] measured in terms of the Ca/Si ratio spanning the range from 1 to 2. CSH is hovever a (defective) layered material for Ca/Si ratio retainting the layered structure of a parent mineral called Tobermorite.…”

“…η 12 and χ 12 characterize anisotropic interactions of particles due to their shapes and relative orientations. In the case of clay platelets, the PMF for face-to-face interactions between layers following the procedure of Ebrahimi et al [7], is given in Figure 2. It represents the change in system free energy at 300K as a function of the distance between layer and is given as an energy per surface area hence allowing the scaling as a function of the particle size.…”

Physical Origins of Thermal Properties of Cement Paste

“…IV and V, we explored the effect of chemistry on the nanoscale equilibrium and nonequilibrium thermophysical properties of various calcium-silicate phases present in cement paste. In this section, we employ multiscale modeling techniques to link the nanoscale properties of individual constituent phases of cement paste to macroscale properties [79,[99][100][101][102][103]. The upscaling of specific-heat capacity from the atomic scale (level 0) to the macroscale (level 3) is rather straightforward.…”