Extended Ensemble Approach to Transferable Potentials for Low Resolution Coarse-Grained Models of Ionomers

被引:14
作者
Rudzinski, Joseph F. [1 ,3 ]
Lu, Keran [2 ]
Milner, Scott T. [2 ]
Maranas, Janna K. [2 ]
Noid, William G. [1 ]
机构
[1] Penn State Univ, Dept Chem, University Pk, PA 16802 USA
[2] Penn State Univ, Dept Chem Engn, University Pk, PA 16802 USA
[3] Max Planck Inst Polymer Res, D-55128 Mainz, Germany
基金
美国国家科学基金会;
关键词
MOLECULAR-DYNAMICS SIMULATIONS; SINGLE-ION CONDUCTORS; BORN-GREEN METHOD; HYDRATED IONS; FORCE-FIELD; SYSTEMS; MELTS; ALGORITHMS; EFFICIENT; COMPUTER;
D O I
10.1021/acs.jctc.6b01160
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We develop an extended ensemble method for constructing transferable, low-resolution coarse-grained (CG) models of polyethylene-oxide (PEO)-based ionomer chains with varying composition at multiple temperatures. In particular, we consider ionomer chains consisting of 4 isophthalate groups, which may be neutral or sulfonated, that are linked by 13 PEO repeat units. The CG models represent each isophthalate group with a single CG site and also explicitly represent the diffusing sodium counterions but do not explicitly represent the PEO backbone. We define the extended ensemble as a collection of equilibrium ensembles that are obtained from united atom (UA) simulations at 2 different temperatures for 7 chemically distinct ionomers with varying degrees of sulfonation. We employ a global force-matching method to determine the set of interaction potentials that, when appropriately combined, provide an optimal approximation to the many-body potential of mean force for each system in the extended ensemble. This optimized xn force field employs 'long-ranged Coulomb potentials with system-specific dielectric constants that systematically decrease with increasing sulfonation and temperature. An empirical exponential model reasonably describes the sensitivity of the dielectric to sulfonation, but we find it more challenging to model the temperature-dependence of the dielectrics. Nevertheless, given appropriate dielectric constants,the transferable xn force field reasonably describes the ion pairing that is observed in the UA simulations as a function of sulfonation and temperature. Remarkably, despite eliminating any explicit description of the PEO backbone, the CG model predicts string-like ion aggregates that appear qualitatively consistent with the ionomer peak observed in X-ray scattering experiments and, moreover, with the temperature dependence of this peak.
引用
收藏
页码:2185 / 2201
页数:17
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