Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
Department of Materials Science and Engineering and Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Chem Phys. 2019 Feb 14;150(6):064901. doi: 10.1063/1.5085069.
We performed microsecond-long, atomistic molecular dynamics simulations on a series of precise poly(ethylene-co-acrylic acid) ionomers neutralized with lithium, with three different spacer lengths between acid groups on the ionomers and at two temperatures. Ionic aggregates form in these systems with a variety of shapes ranging from isolated aggregates to percolated aggregates. At the lower temperature of 423 K, the ionic aggregate morphologies do not reach a steady-state distribution over the course of the simulations. At the higher temperature of 600 K, the aggregates are sufficiently mobile that they rearrange and reach steady state after hundreds of nanoseconds. For systems that are 100% neutralized with lithium, the ions form percolated aggregates that span the simulation box in three directions, for all three spacer lengths (9, 15, and 21). In the partially neutralized systems, the morphology includes lithium ion aggregates that may also include some unneutralized acid groups, along with a coexisting population of acid group aggregates that form through hydrogen bonding. In the lithium ion aggregates, unneutralized acid groups tend to be found on the ends or sides of the aggregates.
我们对一系列用锂中和的具有不同酸基团间隔长度的精确聚（乙烯-co-丙烯酸）离聚物进行了微秒级的原子分子动力学模拟，在两个温度下进行。在这些体系中形成了各种形状的离子聚集体，从孤立的聚集体到渗透的聚集体。在较低的温度 423 K 下，离子聚集体形态在模拟过程中没有达到稳定的分布。在较高的温度 600 K 下，聚集体足够移动，在数百纳秒后它们会重新排列并达到稳定状态。对于 100%用锂中和的系统，离子形成渗透聚集体，在三个方向上跨越模拟盒，对于所有三种间隔长度（9、15 和 21）都是如此。在部分中和的系统中，形态包括可能还包含一些未中和的酸基团的锂离子聚集体，以及通过氢键形成的共存的酸基团聚集体。在锂离子聚集体中，未中和的酸基团往往存在于聚集体的末端或侧面。
