The Pennsylvania State University, 120 Fenske Laboratory, University Park, Pennsylvania 16802, USA.
J Chem Phys. 2017 Feb 14;146(6):064901. doi: 10.1063/1.4973931.
Ionomers are polymers in which an ionic group is covalently bonded to the polymer backbone. Ion aggregates in ionomers have morphologies that allow for the packing of the attached polymer backbone. Using ion-only coarse-grained molecular dynamics, we observe that string-like ion aggregates become flat and sheet-like at lower dielectric constants. A consequence of the changing morphology is that the sheet-like aggregates self-assemble to form ordered, lamellar structures. We use a simple thermodynamic model to demonstrate that depletion attraction mediated by small aggregates can explain the observed order. Our results suggest that depletion attraction can drive ions to form structures that have the size scale suggested by direct visualization, produce the commonly observed experimental correlation peak from X-ray and neutron scattering, and satisfy chain-packing constraints that have been demonstrated to be important in simulations.
离聚物是指聚合物主链上通过共价键连接有离子基团的聚合物。离聚物中的离子聚集体具有特定的形态，使得与之相连的聚合物主链能够进行有序的堆积。我们使用仅含离子的粗粒化分子动力学模拟方法发现，在较低介电常数下，线状的离子聚集体会变得扁平并呈现片状形态。这种形态的变化导致片状聚集体自组装形成有序的层状结构。我们使用一个简单的热力学模型证明，由小聚集体介导的空间位阻排斥力可以解释观察到的有序现象。我们的结果表明，空间位阻排斥力可以促使离子形成具有直接可视化所建议的大小尺度的结构，产生 X 射线和中子散射实验中常见的相关峰，并满足链堆积约束，这些约束在模拟中被证明是非常重要的。
