Molecular dynamics simulation of ODTMA-Montmorillonite and nylon 6 nanocomposites

摘要

Polymer materials stand on a very significant position in the materials industry area.The presence of organoclay nanocomposites reinforces polymer materials on manyproperties like strength, tensile and so on. Most previous studies on the characteristicsof organoclays and polymer nanocomposites were based on the experimentalapproaches such as XRD (X-ray Diffraction) and NMR (Nuclear MagneticResonance). These methods have achieved successfully on the basic analysis ofchains and layering structures of polymer nanocomposites. However, information onthe molecular level cannot be provided by those approaches. MD (MolecularDynamic) simulation method could be employed to develop further information onthe molecular level about organoclays and interlayer structure polymernanocomposites.In the research of ODTMA-MMT (Octadecyltrimethylammonium-Montmorillonite)organoclay simulation, we find that the strong layering behaviour of interlayerODTMA molecules is present with the same minimum distance between nitrogenatoms and MMT surface in different T/O (Tetrahedral vs. Octahedral) ratio cases.Nitrogen atoms sit right above the corresponding hexagonal cavities, which is inagreement with the previous research. The interaction energy between surfactants andMMT clay will reach the lowest point when substitution ratio of tetrahedral andoctahedral (T/O) is equal to 1:1. Moreover, MSD (Mean Square Displacement) anddiffusion coefficient of different models under same CEC (Charge Exchange Capacity)condition are inverse ratio to the T/O proportion.In nylon6 polymer nanocomposites, sodium cations which exist originally inensemble as charge balancer are absorbed much closer to MMT surface than theorganic components in the nylon 6 ODTMA-MMT ensemble. Sodium atoms ornitrogen atoms in surfactants both have higher MSD and coefficients than those atomsin the organic-modified clays. In the exfoliated nylon 6 ODTMA-MMTnanocomposites, pair correlation has been analysed instead of density profile.Layering packing structure is also shown through this analysis, which is alsoconsistent with previous work.