A molecular dynamics study on the structural and mechanical properties of pyrophyllite and M-Montmorillonites (M = Na, K, Ca, and Ba)

ZF Han and H Yang and MH Bu and MC He, CHEMICAL PHYSICS LETTERS, 803, 139848 (2022).

DOI: 10.1016/j.cplett.2022.139848

In this work, molecular dynamics simulations were performed to reveal the effects of interlayer cations (Na+, K+, Ca2+, Ba2+) on the structural and mechanical properties of montmorillonites (MMTs) and the obtained results were compared with those of pyrophyllite without isomorphous substitutions. Lattice parameters, interlayer spacing and equilibrium volumes were calculated. Based on the stress-strain curve obtained by uniaxial compression, ultimate stress and strain, Poisson's ratio and Young's modulus along three crystal directions were calculated. The obtained results revealed that the mechanical properties of pyrophyllite and MMTs were obviously different and the type of interlayer cations significantly affected the mechanical properties of MMTs, especially along OC direction. The negative correlation between ultimate strain and charge/ionic radius ratio well explains the particularity of the stress-strain curves of K-MMT and Ba-MMT. Moreover, distribution of counterions between layers and their interactions with clay sheets were analyzed and radial distribution function and number density profiles perpendicular to clay surface were calculated.

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