Controlling Clay Swelling-Shrinkage with Inorganic Nanoparticles: A Molecular Dynamics Study
LS de Lara and VA Rigo and CR Miranda, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 20266-20271 (2017).
The control of clay swelling can be achieved by using nanoparticles. This paper describes the use of atomistic" molecular dynamics simulations to study the interaction of SiO2 nanoparticles (NPs) with Na-montmorillonite (MMT) clay platelets. The NP5@MMT interfaces were simulated by taking into account different aqueous solutions (NaCI and CaCl2) and three different coverages for NPs (hydroxylated, PEGlyated, and sulfonated). The formation of electric double layers (EDL) was observed on the NP and MMT surfaces. The free energies as a function of the NP platelet distance were determined for each interface, while global minima near MMT surfaces and local minima in the middle path were observed. The presence of NPs in the local (dispersed) or global energy minima (adsorbed) leads to a broadening and compressing of the EDLs, respectively. Accordingly, a mechanism for this swelling shrinkage can be proposed, based on changes in the EDLs caused by NPs. Because of overlap between the EDLs, for the adsorbed NP the ion accumulation on the MMT surface increases, resulting in an attractive potential and compression of the clay. This MMT swelling shrinkage transition leads to interplatelet distance changes of which is consistent with the results of previous studies. These indicate an effective way to use NPs to tune clay swelling inhibition.
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