Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Soft Matter. 2018 Nov 21;14(45):9282-9295. doi: 10.1039/c8sm01358f.
We demonstrate the potential of hybrid particle-based models, where interactions are introduced through functionals of local order parameters, in describing multicomponent polymer solutions. The link to a free-energy-like functional is advantageous for controlling the thermodynamics of the model. We focus on co-non-solvency - the collapse of polymer chains in dilute mixtures with two miscible good solvents, having different affinities towards the polymer. We employ a simple model where polymers and solvents are represented, respectively, by worm-like chains and single particles. Non-bonded interactions are captured by a polynomial which is third order in local densities and can, therefore, describe liquid-vapour coexistence. The parameterisation of the functional benefits from an elementary mean-field approximation to the statistical mechanics of the model. The model provides a framework for Monte Carlo simulations using a particle-to-mesh algorithm. Studies with conventional generic bead-spring and all-atom models have demonstrated that co-non-solvency is caused by preferential binding of the better solvent (termed cosolvent) with polymer. Hence, segmental loops bridged by cosolvent molecules are formed, initiating polymer collapse. The mesoscopic hybrid model differs conceptually from the conventional microscopic descriptions. Yet, it reproduces the same co-non-solvency mechanism supporting its universality. Films of adsorbed ternary solutions, showing co-non-solvency in the dilute regime, are considered at high concentrations. In this case, chains do not collapse. The properties of loops and tails of the adsorbed polymer agree with early theoretical predictions obtained for concentrated binary solutions.
我们展示了混合粒子模型的潜力，其中通过局部序参量的泛函引入相互作用，以描述多组分聚合物溶液。与自由能泛函的联系有利于控制模型的热力学。我们专注于共非溶剂性——在与两种混溶性良溶剂的稀混合物中聚合物链的塌陷，这两种良溶剂对聚合物的亲和力不同。我们采用了一种简单的模型，其中聚合物和溶剂分别由蠕虫状链和单粒子表示。非键相互作用由多项式捕获，该多项式在局部密度中是三阶的，因此可以描述液-汽共存。泛函的参数化得益于模型统计力学的基本平均场近似。该模型为使用粒子到网格算法的蒙特卡罗模拟提供了一个框架。使用传统的通用珠-簧和全原子模型的研究表明，共非溶剂性是由更好溶剂（称为共溶剂）与聚合物的优先结合引起的。因此，由共溶剂分子桥接的链段环形成，引发聚合物塌陷。介观混合模型在概念上与传统的微观描述不同。然而，它再现了相同的共非溶剂性机制，支持其普遍性。在高浓度下考虑了显示稀溶液中具有共非溶剂性的吸附三元溶液的薄膜。在这种情况下，链不会塌陷。吸附聚合物的环和尾部的性质与针对浓缩二元溶液获得的早期理论预测一致。
