Conformational and Dynamic Properties of Poly(ethylene
oxide) in BMIM+BF4–: A Microsecond
Computer Simulation Study Using ab Initio Force Fields
Posted on 2018-07-11 - 19:36
The
behavior of polymers in complex solvents is interesting from
a fundamental perspective and of practical importance from the standpoint
of polymer processing. There has been recent interest in the conformational
and dynamic properties of polymer in room temperature ionic liquids,
with conflicting predictions from computations using models with different
resolutions and conflicting results of experiments from different
groups. In this work, we develop a first-principles, nonpolarizable
united atom (UA) force field for a mixture of poly(ethylene oxide)
(PEO) in the ionic liquid BMIM+BF4–. The UA force field
is benchmarked against ab initio calculations, and the PEO atomic
charges are parametrized to implicitly capture the polarization contribution
to the solvation energy of a single PEO molecule in BMIM+BF4–. The UA model allows one to perform multi-microsecond molecular
dynamics simulations. This is necessary because the conformational
relaxation correlation times are of the order of 100 ns. The simulations
predict that the radius of gyration, Rg, scales with molecular weight, Rg ∼ Mwν with ν ≈ 0.56 in the temperature range 300–600
K, consistent with experiment, seemingly in between a self-avoiding
walk and an ideal chain. An examination of the snapshots of the polymer
demonstrates, however, that the polymer conformations are composed
of ringlike and linear segments, with ringlike parts of the chain
wrapped around cations of the ionic liquid. The slow dynamics arises
from the barrier to unwrapping the ringlike segments of the polymer.
The mean-square displacement shows three regimes which we interpret
as confinement, Zimm, and diffusive. The simulations emphasize the
importance of accurate force fields and microsecond simulations in
obtaining reliable results for polymers and elucidate important correlation
effects for polymers in strongly interacting solvents.
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Son, Chang
Yun; McDaniel, Jesse G.; Cui, Qiang; Yethiraj, Arun (2018). Conformational and Dynamic Properties of Poly(ethylene
oxide) in BMIM+BF4–: A Microsecond
Computer Simulation Study Using ab Initio Force Fields. ACS Publications. Collection. https://doi.org/10.1021/acs.macromol.8b01002
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AUTHORS (4)
CS
Chang
Yun Son
JM
Jesse G. McDaniel
QC
Qiang Cui
AY
Arun Yethiraj
KEYWORDS
BFringlike partssolvation energycorrelation effectsBMIMrelaxation correlation timespolymer conformationsforce fieldsUA modelforce fieldR gDynamic PropertiesMicrosecond Computer Simulation Studyab initio calculationsringlike segmentsUA force fieldpolymer processingmicrosecond simulationsPEO moleculepolarization contributionab Initio Force Fieldsdynamics simulationsroom temperature100 ns