Short chain branched (SCB) polyolefins as a model of metallocene ethylene/R-olefin copolymers were simulated by Monte Carlo (MC) and molecular dynamics (MD) methods. Melt density, which was evaluated by MD in the isothermal-isobaric ensemble (NPT-MD), slightly increases with the SCB content. A mix of different MC moves was adopted and connectivity-altering moves, such as end-bridging, were modified in order to incorporate the branches into the simulation. This MC simulation strategy performed very well in equilibrating molten SCB copolymers at all length scales. The chain size and local packing in the melt, as obtained from the MC simulations, are discussed. At given backbone length, chain size, as quantified by the radius of gyration, decreases with the number of branches. On the other hand, the presence of short branches leads to a less effective intermolecular local packing in the melt. Rheological properties of the copolymers are discussed based on a mapping of the Monte Carlo atomistic simulations on the packing length model, and compared with experimental results. In general, good agreement with experimental results is found.

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The microscopic structure, thermodynamic properties, local segmental dynamics, and self-diffusion coefficients of three ionic liquids (ILs) with a common anion, namely, the bis(trifluoromethylsulfonyl) imide ([Tf2N-]), and imidazolium-based cations that differ in the alkyl tail length, namely, the 1-butyl-3-methylimidazolium ([C4mim+]), the 1-hexyl-3-methylimidazolium ([C6mim+]), and the 1-octyl-3-methylimidazolium ([C8mim+]), are calculated over the temperature range of 298.15-333.15 K and pressure range of 0.1-60 MPa. Quantum calculations based on density functional theory are performed on isolated ion pairs, and minimum energy conformers are identified. Electronic density results are used to estimate the electrostatic potential of a molecular force field that is used subsequently for long molecular dynamics (MD) simulations of bulk ILs. Thermodynamic properties calculated from MD are shown to be in excellent agreement for the bulk density and good agreement for derivative properties when compared to experimental data. The new force field is an improvement over earlier ones for the same ILs. The microscopic structure as expressed through the radial distribution function is thoroughly calculated, and it is shown that the bulk structure characteristics are very similar to those obtained from the quantum calculations on isolated ion pairs. The segmental dynamics expressed in terms of bond and torsion angle decorrelation is shown to assume a broad range of characteristic times. Molecular segments in the alkyl tail of the cations are significantly faster than segments in the vicinity of the imidazolium ring. Finally, the new force field predicts accurately the self-diffusion coefficients of the cations and the anions over the entire temperature range examined, thus confirming its validity for a broad range of physical properties.