He Gui-Li, Merlitz Holger, Sommer Jens-Uwe
Leibniz-Institut für Polymerforschung Dresden, 01069 Dresden, Germany.
J Chem Phys. 2014 Mar 14;140(10):104911. doi: 10.1063/1.4867466.
Molecular dynamics simulations are applied to investigate salt-free planar polyelectrolyte brushes under poor solvent conditions. Starting above the Θ-point with a homogeneous brush and then gradually reducing the temperature, the polymers initially display a lateral structure formation, forming vertical bundles of chains. A further reduction of the temperature (or solvent quality) leads to a vertical collapse of the brush. By varying the size and selectivity of the counterions, we show that lateral structure formation persists and therefore demonstrate that the entropy of counterions being the dominant factor for the formation of the bundle phase. By applying an external compression force on the brush we calculate the minimal work done on the polymer phase only and prove that the entropy gain of counterions in the bundle state, as compared to the homogeneously collapsed state at the same temperature, is responsible for the lateral microphase segregation. As a consequence, the observed lateral structure formation has to be regarded universal for osmotic polymer brushes below the Θ-point.
应用分子动力学模拟来研究在不良溶剂条件下的无盐平面聚电解质刷。从高于θ点开始，以均匀的刷子为起始状态，然后逐渐降低温度，聚合物最初呈现出横向结构形成，形成垂直的链束。进一步降低温度（或溶剂质量）会导致刷子的垂直塌陷。通过改变抗衡离子的大小和选择性，我们表明横向结构形成持续存在，因此证明抗衡离子的熵是形成束相的主导因素。通过对刷子施加外部压缩力，我们仅计算在聚合物相上所做的最小功，并证明与相同温度下均匀塌陷状态相比，束状态下抗衡离子的熵增是横向微相分离的原因。因此，对于低于θ点的渗透聚合物刷，观察到的横向结构形成必须被视为普遍现象。
