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 SiO<sub>2</sub> nanoparticles (NPs) with
Na-montmorillonite (MMT) clay platelets. The NPs@MMT interfaces were
simulated by taking into account different aqueous solutions (NaCl
and CaCl<sub>2</sub>) 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 ∼20%, which is consistent with the results
of previous studies. These indicate an effective way to use NPs to
tune clay swelling inhibition