We performed long-time all-atom molecular dynamics simulations of cationic polymerized ionic liquids with eight mobile counterions, systematically varying size and shape to probe their influence on the decoupling of conductivity from polymer segmental dynamics. We demonstrated rigorous identification of the dilatometric glasstransition temperature (T g ) for polymerized ionic liquids using an all-atom force field. Polymer segmental relaxation rates are presumed to be consistent for different materials at the same glass-transition-normalized temperature (T g /T), allowing us to extract a relative order of decoupling by examining conductivity at the same T g /T. Size, or ionic volume, cannot fully explain decoupling trends, but within certain geometric and chemical-specific classes, small ions generally show a higher degree of decoupling. This size effect is not universal and appears to be overcome when structural results reveal substantial coordination delocalization. We also reveal a universal inverse correlation between ion-association structural relaxation time and absolute conductivity for these polymerized ionic liquids, supporting the ion-hopping interpretation of ion mobility in polymerized ionic liquids.

No abstract

Simulations are performed using the reverse non-equilibrium molecular dynamics (rNEMD) method and the Stillinger-Weber (SW) potential to determine the input parameters for achieving ±1% convergence of the calculated thermal conductivity of silicon. These parameters are then used to investigate the effects of the interatomic potentials of SW, Tersoff II, Environment Dependent Interatomic Potential (EDIP), Second Nearest Neighbor, Modified Embedded-Atom Method (MEAM), and Highly Optimized Empirical Potential MEAM on determining the bulk thermal conductivity as a function of temperature (400–1000 K). At temperatures > 400 K, data collection and swap periods of 15 ns and 150 fs, system size ≥6 × 6 UC2 and system lengths ≥192 UC are adequate for ±1% convergence with all potentials, regardless of the time step size (0.1–0.5 fs). This is also true at 400 K, except for the SW potential, which requires a data collection period ≥30 ns. The calculated bulk thermal conductivities using the rNEMD method and the EDIP potential are close to, but lower than experimental values. The 10% difference at 400 K increases gradually to 20% at 1000 K.

No abstract

No abstract