Molecular dynamics simulation of thermomechanical properties of montmorillonite crystal. 3. montmorillonite crystals with PEO oligomer intercalates.

We present the results of molecular dynamics (MD) simulation of the structure and thermomechanical behavior of Wyoming-type Na+-montmorillonite (MMT) with poly(ethylene oxide) (PEO) oligomer intercalates. Periodic boundary conditions in all three directions and simulation cells containing two MMT lamellae [Si248Al8][Al112Mg16]O640[OH]128 oriented parallel to the XY-plane were used. The interlamellar space, or gallery, between neighboring MMT lamellae was populated by 24 Na+ counterions and PEO macromolecules of different lengths, ranging from 2 up to 240 repeat units. We considered three different loadings of PEO within the gallery: 80, 160, and 240 repeat units, corresponding to 13, 23, and 31 wt % PEO based on total mass of the nanocomposite, respectively. In the cases of 13 and 23 wt %, the polymer chains formed one or two well-defined amorphous layers with interlayer distances of 1.35 and 1.8 nm, respectively. We have observed also formation of a wider monolayer gallery with interlayer distances of 1.6 nm. Three-layer PEO films formed in the case of 31 wt % loading. The thermal properties were analyzed over the range 300-400 K, and the isothermal linear compressibility, transversal moduli, and shear moduli were calculated at 300 K. These properties are compared with the results of our simulation of thermal and mechanical properties of MMT crystal with galleries filled by one or two water layers as well as with those of an isolated clay nanoplate.