Karatrantos Argyrios V, Khantaveramongkol Jettawat, Kröger Martin
Materials Research and Technology, Luxembourg Institute of Science and Technology, 5, Avenue des Hauts-Fourneaux, L-4362 Esch-sur-Alzette, Luxembourg.
Polymer Physics, Department of Materials, ETH Zurich, Leopold-Ruzicka-Weg 4, CH-8093 Zurich, Switzerland.
Polymers (Basel). 2022 Jul 29;14(15):3070. doi: 10.3390/polym14153070.
Ionic polymers exhibit mechanical properties that can be widely tuned upon selectively charging them. However, the correlated structural and dynamical properties underlying the microscopic mechanism remain largely unexplored. Here, we investigate, for the first time, the structure and diffusion of randomly and end-functionalized ionic poly(dimethylsiloxane) (PDMS) melts with negatively charged bromide counterions, by means of atomistic molecular dynamics using a united atom model. In particular, we find that the density of the ionic PDMS melts exceeds the one of their neutral counterpart and increases as the charge density increases. The counterions are condensed to the cationic part of end-functionalized cationic PDMS chains, especially for the higher molecular weights, leading to a slow diffusion inside the melt; the counterions are also correlated more strongly to each other for the end-functionalized PDMS. Temperature has a weak effect on the counterion structure and leads to an Arrhenius type of behavior for the counterion diffusion coefficient. In addition, the charge density of PDMS chains enhances the diffusion of counterions especially at higher temperatures, but hinders PDMS chain dynamics. Neutral PDMS chains are shown to exhibit faster dynamics (diffusion) than ionic PDMS chains. These findings contribute to the theoretical description of the correlations between structure and dynamical properties of ion-containing polymers.
离子聚合物表现出的机械性能可在对其进行选择性充电时得到广泛调节。然而，微观机制背后相关的结构和动力学性质在很大程度上仍未得到探索。在此，我们首次借助采用联合原子模型的原子分子动力学方法，研究了带有带负电荷溴化物抗衡离子的无规和端基官能化离子型聚二甲基硅氧烷（PDMS）熔体的结构与扩散。特别地，我们发现离子型PDMS熔体的密度超过其相应中性熔体的密度，且随着电荷密度的增加而增大。抗衡离子凝聚在端基官能化阳离子PDMS链的阳离子部分，尤其是对于较高分子量的情况，导致在熔体内部扩散缓慢；对于端基官能化的PDMS，抗衡离子之间的相互关联也更强。温度对抗衡离子结构的影响较弱，并且抗衡离子扩散系数呈现出阿仑尼乌斯型行为。此外，PDMS链的电荷密度尤其在较高温度下会增强抗衡离子的扩散，但会阻碍PDMS链的动力学。结果表明，中性PDMS链比离子型PDMS链表现出更快的动力学（扩散）。这些发现有助于从理论上描述含离子聚合物结构与动力学性质之间的相关性。
