Comparison of the effect of poly(N-vinyl caprolactam) and poly(N-isopropyl acrylamide) trimers on the stability of hydrated Na-montmorillonite: A molecular dynamics study - 徐加放教授课题组

In the present study, we performed a molecular dynamics simulation of the intercalation of poly( N-isopropyl acrylamide) (NIPAM)3 and poly( N-vinyl caprolactam) (NVCL)3 trimers into Na-montmorillonite (Na-Mt) to evaluate their effects on the interlayer structure and the stability of hydrated Na-Mt. The impact of both trimers on the interlayer species and their dynamics properties at different temperatures in a canonical ensemble (NVT) were investigated. The results showed that the electrostatic forces exerted by Na cations on H2O molecules and the interlayer H2O molecular arrangement are not affected by the rise in temperature after adding both trimers. Trimer addition reinforced the structure of interlayer H2O molecules so that the effect of temperature increase on them became negligible. The structural dynamics evolution of the radius of gyration of both trimers showed the existence of conformation changes when temperature increased. These conformational changes are more complex in the case of (NVCL)3 than (NIPAM)3 due to its large monomers. Both trimers reduced the mobility of interlayer particles with a better inhibition effect obtained for (NVCL)3 compared to (NIPAM)3. The concentration profile of interlayers’ species showed the affinity of Na cations for clay mineral surfaces while H2O molecules moved away. Compared these two trimers, the most stable state of Na-Mt is achieved with (NVCL)3. These results could help highlight the inhibition properties of (NIPAM)3 and (NVCL)3 on hydrated Na-Mt and to predict its stability against changes in environmental conditions.