Abstract

A generic coarse-grained bead-and-spring model, mapped onto comb-shaped polycarboxylate-based (PCE) superplasticizers, is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions. The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution. The effects of ionic strength, side-chain number, and side-chain length on the conformational behavior of PCEs in solution are explored. Single-chain equilibrium properties, including the radius of gyration, end-to-end distance and persistence length of the polymer backbone, shape-asphericity parameter, and the mean span dimension, are determined. It is found that with the increase of ionic strength, the equilibrium sizes of the polymers decrease only slightly, and a linear dependence of the persistence length of backbone on the Debye screening length is found, in good agreement with the theory developed by Dobrynin. Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes (radius of gyration and mean span) of the polymer as a whole, but also the persistence length of the backbone due to excluded volume interactions.

中文翻译：

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用粗粒珠-弹簧模型研究带负电主链和中性侧链的梳状聚电解质的构象性质

摘要

通过兰格文分子动力学模拟，在隐含溶剂和显性抗衡离子的作用下，开发并研究了映射到梳形聚羧酸基（PCE）高效减水剂的通用粗粒珠和弹簧模型。PCE的回转半径与实验的一致性表明，我们的模型可用于研究溶液中PCE的平衡尺寸。探索了离子强度，侧链数和侧链长度对溶液中PCE构象行为的影响。确定了单链平衡特性，包括回转半径，聚合物主链的端到端距离和持久长度，形状非球面度参数以及平均跨度。发现随着离子强度的增加，聚合物的平衡尺寸仅略有减小，并且发现骨架的持久性长度对Debye筛选长度的线性依赖性，与Dobrynin提出的理论高度吻合。增加侧链数目和/或侧链长度不仅增加了聚合物整体的平衡尺寸（回转半径和平均跨度），而且由于排除了体积相互作用，还增加了主链的持久长度。