Molecular dynamics simulation of the crystalline short-chain polymer system LiPF6•PEO6 (Mw ∼ 1000)

In an effort to probe the effect of chain length on the structure and properties of ionically conducting polymer electrolytes, the crystalline system (LiPF6PEO6)-P-. has been simulated at 293 K using the Molecular Dynamics Simulation (MDS) technique. The specific system studied is short-chain poly( ethylene oxide) with the formulation CH3-(OCH2CH2)(22) - OCH3; M-w = 1015, a commercially available mono-disperse short-chain PEO form resembling that studied experimentally (Stoeva et al., J. Am. Chem. Soc., 2003, 125, 4619, ref. 27). The methoxy chain-ends have been arranged to reproduce smectic and nematic models. Calculated Li+ ion coordination, polymer chain configuration, chain-end registry and diffraction profiles are compared both with experiment and with the results from earlier MD simulations of infinite PEO chain systems ( Brandell et al., J. Mater. Chem., 2005, 15, 1422, ref. 30). The differences found are interpreted in the terms of chain-end effects and polymer relaxation.