Extended Ensemble Approach to Transferable Potentials for Low-Resolution Coarse-Grained Models of Ionomers
Extended Ensemble Approach to Transferable Potentials for Low-Resolution Coarse-Grained Models of Ionomers
复制标题
低分辨率粗粒度离聚物模型可转移势的扩展系综方法
DOI：
10.1021/acs.jctc.6b01160
复制
发表时间：
2017
影响因子：
5.5
通讯作者：
Noid, William G.
中科院分区：
文献类型：
--
作者：
Rudzinski, Joseph F.;Lu, Keran;Milner, Scott T.;Maranas, Janna K.;Noid, William G.
我们开发了一种扩展的合奏方法，用于构建可转移的，低分辨率的粗粒度（CG）模型的聚氧化乙烯（PEO）为基础的离聚物链在多个温度下具有不同的组成。特别是，我们认为离聚物链组成的4个羟基，这可能是中性或磺化，这是由13个PEO重复单元连接。CG模型代表每个具有单个CG位点的双酸酯基团，并且还明确表示扩散钠抗衡离子，但不明确表示PEO主链。我们定义的扩展合奏作为一个集合的平衡合奏，从联合原子（UA）模拟在2个不同的温度为7个化学性质不同的离聚物与不同程度的磺化。我们采用了一个全球性的力匹配的方法来确定一组相互作用的潜力，当适当的组合，提供了一个最佳的近似的多体潜力的平均力为每个系统在扩展合奏。这种优化的xn力场采用长程库仑势与系统特定的介电常数，系统地随着磺化和温度的增加而降低。经验指数模型合理地描述了电介质对磺化的敏感性，但我们发现它更具有挑战性的模型的温度依赖性的磺化。然而，给定适当的介电常数，可转移的xn力场合理地描述了在UA模拟中观察到的离子配对作为磺化和温度的函数。值得注意的是，尽管消除了任何明确的描述的PEO骨干，CG模型预测字符串样的离子聚集体，出现定性一致的离聚物峰中观察到的X-射线散射实验，而且，与温度的依赖性，这个峰值。
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.