Carlsson P, Andersson D, Swenson J, McGreevy R L, Howells W S, Börjesson L
Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
J Chem Phys. 2004 Dec 15;121(23):12026-37. doi: 10.1063/1.1815295.
The structure of an amorphous polymer electrolyte, poly(propylene oxide) (PPO) complexed with LiClO4, has been studied using reverse Monte Carlo (RMC) simulations. The simulations require no force field but are based on experimental data only, in this case from x-ray and neutron diffraction experiments. Excellent agreement between the experimental data and the structures resulting from the RMC simulation is obtained. Samples with ether-oxygen to lithium concentrations (molar ratios) O:Li=16:1 and 5:1 were studied and compared to results of pure PPO from a previous study. We focus on the effects of the solvated salt on the structure of the polymer matrix, the spatial distribution of ions, and the correlations between the anions and the polymer chains. Analyzing the structures produced in the simulations, we find that for a concentration 16:1, the interchain distance is approximately the same as in pure PPO but more well defined. For a concentration 5:1, we find a larger and less well-defined interchain distance compared to the 16:1 concentration. This signifies that at the 16:1 salt concentration, there is enough free volume in the polymer host to accommodate the ions, and that the solvation of salt induces ordering of the polymer matrix. At the higher salt concentration 5:1, the polymer network must expand and become less ordered to host the ions. We also note, in accordance with previous studies, that the solvation of salt changes the conformation of the polymer chain towards more gauche states. The simulations furthermore reveal marked correlations between the polymer chains and the anions, which we suggest arise predominantly from an interaction mediated via cations, which can simultaneously coordinate both ether oxygens in the polymer chains and anions. Interanionic distances at 5 A, which are consistent with two or more anions being coordinated around the same cation, are also observed. On a larger scale, the RMC structure of PPO-LiClO4 16:1 clearly indicates the presence of salt-rich and salt-depleted domains having a length scale of <20 A. In view of such a heterogeneous structure of PPO-LiClO4 16:1, it is plausible that the increased ordering of the polymer matrix is due to rather well-defined structural arrangements within the salt-rich domains, and that the characteristic interchain distance in the salt-rich domains is similar to that of the pure polymer.
采用反向蒙特卡罗（RMC）模拟研究了与高氯酸锂络合的非晶态聚合物电解质聚环氧丙烷（PPO）的结构。该模拟不需要力场，仅基于实验数据，在此情况下是来自X射线和中子衍射实验的数据。实验数据与RMC模拟得到的结构之间取得了极好的一致性。研究了醚氧与锂浓度（摩尔比）为O:Li = 16:1和5:1的样品，并与先前研究中纯PPO的结果进行了比较。我们关注溶剂化盐对聚合物基体结构、离子的空间分布以及阴离子与聚合物链之间相关性的影响。通过分析模拟产生的结构，我们发现对于浓度为16:1的情况，链间距离与纯PPO中的大致相同，但更明确。对于浓度为5:1的情况，与16:1浓度相比，我们发现链间距离更大且更不明确。这表明在盐浓度为16:1时，聚合物主体中有足够的自由体积来容纳离子，并且盐的溶剂化诱导了聚合物基体的有序化。在较高的盐浓度5:1时，聚合物网络必须扩展并变得更无序以容纳离子。我们还注意到，与先前的研究一致，盐的溶剂化使聚合物链的构象向更多的gauche状态转变。模拟还揭示了聚合物链与阴离子之间明显的相关性，我们认为这主要源于通过阳离子介导的相互作用，阳离子可以同时配位聚合物链中的两个醚氧和阴离子。还观察到5埃的阴离子间距离，这与两个或更多阴离子围绕同一阳离子配位一致。在更大的尺度上，PPO-LiClO4 16:1的RMC结构清楚地表明存在长度尺度小于20埃的富盐和贫盐区域。鉴于PPO-LiClO4 16:1的这种非均相结构，聚合物基体有序化增加可能是由于富盐区域内相当明确的结构排列，并且富盐区域内的特征链间距离与纯聚合物的相似。
