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Peter Daivis

Publications and source records attributed to Peter Daivis.

2 recordsLinked to original sources

Molecular dynamics simulation of high slip flow of water confined between graphene nanochannels at experimentally accessible strain rates

The transient time correlation function method (TTCF) has emerged as a powerful methodology for accurately probing systems at low shear rates. In the present study, TTCF was used to evaluate the shear rate dependence of the slip length in a high-slip system consisting of water confined between graphene walls at experimentally accessible shear rates, for which classical nonequilibrium molecular dynamics (NEMD) is unfeasible. The corresponding Navier friction coefficient was computed for all shear rates spanning six orders of magnitude and compared with the equilibrium limit. We report for the first time NEMD results obtained at experimentally accessible shear rates using the TTCF approach for a system that has attracted significant interest over the past decades. The slip length calculated with TTCF is in good agreement with previous equilibrium molecular dynamics simulations and experiments. Our aim here is to highlight the extraordinary power of TTCF, particularly for high-slip (low strain-rate) systems, and to verify that equilibrium methods directly match NEMD measurements at experimentally accessible strain rates.

physics.chem-ph

Molecular dynamics study of the linear viscoelastic shear and bulk relaxation moduli of poly(tetramethylene oxide) (PTMO)

Here we report the linear viscoelastic properties of amorphous poly(tetramethylene oxide) (PTMO), which is one of the key components in synthesizing segmented polyurethane (PU) elastomers. The temperature and molecular weight dependent viscoelastic behavior is investigated in detail by computing the shear relaxation modulus G(t) and the bulk relaxation modulus K(t), using the Green-Kubo relationship with correlation function. Our results provide new data for PTMO melt from the united atom model and also extend the existing knowledge of viscoelastic properties of polymers in general. The predicted viscoelastic behavior range is shifted on a master curve using the time-temperature superposition principle (TTSP) with horizontal and vertical shift factors. The emerging shift factors agree with the Williams-Landel-Ferry (WLF) equation. For the validation of the united-atom model of PTMO using the TraPPE-UA force field we explored the transport properties and observed a position-dependent diffusion dynamics throughout the polymer chain, which subsequently influences the scaling laws for chain dynamics. These findings are discussed in terms of emerging experimental evidence on position dependent displacement for different chain portions along the chain length.

cond-mat.soft