Department of Mechanical Engineering, Binghamton University, The State University of New York, 4400 Vestal Parkway East, Binghamton, New York 13902, USA.
J Chem Phys. 2018 Sep 7;149(9):094904. doi: 10.1063/1.5045100.
An osmotic ensemble method for dissipative particle dynamics (DPD) is developed for simulating the swelling behavior of polymer networks in aqueous solvent under constant solvent chemical potential, number of polymer beads, pressure, and temperature conditions. We apply a Langevin piston method to control the pressure of the polymer-solvent mixture. Chemical potential equilibrium is achieved via Monte Carlo insertions and deletions of solvent beads based on the total free energy change of the gel. The osmotic ensemble simulation produces swelling kinetics of hydrogels in excellent agreement with that obtained by previous methods but significantly reduces computational costs. The results show gel swelling as a result of the mechanical balance between osmotic pressure induced by the mixing of the polymer and solvent and elastic force originated from the network deformation. The simulations also elucidate the influence of solvent conditions and network topology on the degree of swelling. The bulk modulus of the model gel is probed at different solvency and its behavior is consistent with the prediction of Flory-Rehner theory. The osmotic ensemble DPD will permit the study of mechanical properties of hydrogels in mesoscale simulations and can be extended to model other complex fluid systems in chemical equilibrium under isothermal-isobaric conditions.
本文开发了一种用于耗散粒子动力学（DPD）的渗透组合方法，以模拟在恒定溶剂化学势、聚合物珠数、压力和温度条件下聚合物网络在水溶剂中的溶胀行为。我们应用朗之万活塞方法来控制聚合物-溶剂混合物的压力。根据凝胶的总自由能变化，通过基于溶剂珠的蒙特卡罗插入和删除来实现化学势平衡。渗透组合模拟产生的水凝胶溶胀动力学与先前方法得到的结果非常吻合，但显著降低了计算成本。结果表明，凝胶的溶胀是由聚合物和溶剂混合引起的渗透压与网络变形产生的弹性力之间的力学平衡造成的。模拟还阐明了溶剂条件和网络拓扑结构对溶胀程度的影响。在不同的溶剂化条件下探测了模型凝胶的体积模量，其行为与 Flory-Rehner 理论的预测一致。该渗透组合 DPD 将允许在介观模拟中研究水凝胶的力学性能，并可扩展到模拟其他在等温和等压条件下处于化学平衡的复杂流体系统。
