Monte Carlo and molecular dynamics computer simulations are used to explore the atomic scale structure and dynamics of intercalated PEO/montmorillonite nanocomposites. Particular attention is paid to the configuration of the polymer within these confined spaces. A layered, but disordered and liquid-like, structure is observed, in contrast to the all-trans or helical extended interlayer structures traditionally suggested. The cations primarily reside near the silicate surface. Molecular dynamics simulations also provide information on the interlayer mobility of Li+ ions, which is related to the ionic conductivity in polymer electrolyte nanocomposites.

Articles you may be interested inMolecular-dynamics simulation of the effect of ions on a liquid-liquid interface for a partially miscible mixture An ab initio molecular dynamics study of the S N 2 reaction Cl − +CH 3 Br→CH 3 Cl+Br − Molecular dynamics ͑MD͒ simulations are used to study the static and dynamic properties of 2:1 layered silicates ion exchanged with alkyl-ammonium surfactants. These systems are in the form of oligomeric alkanes grafted by cationic groups on atomically smooth crystalline layers 10 Å thick and several microns wide. The organically modified layers self-assemble parallel to each other to form alternating, well-ordered organic/inorganic multilayers. By studying the systems at the experimentally measured layer separations, computer modeling directly provides the structure and dynamics of the intercalated surfactant molecules. The grafted-chain conformations are also expressed through the trans-gauche conformer ratios and transition frequencies which compare well with Fourier transform infrared spectroscopy ͑FTIR͒ experiments.

The effect of layer charge on the intercalation of poly(ethylene oxide) (PEO) was investigated using a series of reduced-charge montmorillonites and smectites with varying layer charge. The amount of intercalated polymer initially increases with layer charge but then decreases. In contrast, the amount of water present continuously increases. This water is mostly coordinated with the gallery cations. When PEO is intercalated, it replaces water molecules filling the space between the hydrated exchangeable cations. Molecular simulations confirm the experiments and show that the polymer oxygen atoms do not directly associate with the exchangeable cations, which are mostly coordinated to water molecules and surface oxygen atoms.

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Molecular dynamics simulations were used to study the interlayer structure and dynamics of polystyrene (PS) and polystyrene-polyisoprene (PS-PI) block copolymers intercalated in organically modified layered silicates. In the case of PS the polymer chains displace the aliphatic surfactant chains and reside adjacent to the silicate layers. The electrostatic interactions between the aromatic rings on the PS chains and the silicate surface drive the intercalation of the polymer into the host galleries. PI, which lacks such electrostatic interactions, is immiscible (does not intercalate) with the host. There appears to be a minimum number of PS mers for intercalation of PS-PI copolymers to take place. The intercalated copolymer appears to structure inside the host galleries with the PS mers adjacent to the silicate layers and the corresponding PI away from the surface and towards the middle of the gallery. Using the mean square displacements we find that PS is the least mobile species in the galleries with the surfactant chains been the most mobile of all.