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Osmotic pressure in polyelectrolyte solutions: cell-model and bulk simulations
Soft Matter ( IF 3.4 ) Pub Date : 2018-06-22 00:00:00 , DOI: 10.1039/c8sm00654g
Magnus Ullner 1, 2, 3, 4 , Khawla Qamhieh 5, 6, 7, 8, 9 , Bernard Cabane 10, 11, 12, 13
Affiliation  

The osmotic pressure of polyelectrolyte solutions as a function of concentration has been calculated by Monte Carlo simulations of a spherical cell model and by molecular dynamics simulations with periodic boundary conditions. The results for the coarse-grained polyelectrolyte model are in good agreement with experimental results for sodium polyacrylate and the cell model is validated by the bulk simulations. The cell model offers an alternative perspective on osmotic pressure and also forms a direct link to even simpler models in the form of the Poisson–Boltzmann approximation applied to cylindrical and spherical geometries. As a result, the non-monotonic behaviour of the osmotic coefficient seen in simulated salt-free solutions is shown not to rely on a transition between a dilute and semi-dilute regime, as is often suggested when the polyion is modelled as a linear flexible chain. The non-monotonic behaviour is better described as the combination of a finite-size effect and a double-layer effect. Parameters that represent the linear nature of the polyion, including an alternative to monomer concentration, make it possible to display a generalised behaviour of equivalent chains, at least at low concentrations. At high concentrations, local interactions become significant and the exact details of the model become important. The effects of added salt are also discussed and one conclusion is that the empirical additivity rule, treating the contributions from the polyelectrolyte and any salt separately, is a reasonable approximation, which justifies the study of salt-free solutions.

中文翻译:

聚电解质溶液中的渗透压:细胞模型和体积模拟

聚电解质溶液的渗透压随浓度的变化已通过球形细胞模型的蒙特卡洛模拟和具有周期性边界条件的分子动力学模拟计算得出。粗粒聚电解质模型的结果与聚丙烯酸钠的实验结果吻合良好,并且通过大量模拟验证了电池模型。单元模型提供了关于渗透压的另一种观点,并以应用于圆柱和球形几何体的泊松-玻尔兹曼近似形式与更简单的模型建立了直接联系。结果,在模拟的无盐溶液中看到的渗透系数的非单调行为表明它不依赖于稀和半稀溶液之间的过渡,正如通常在将聚离子建模为线性柔性链时所建议的那样。非单调行为可以更好地描述为有限大小效应和双层效应的组合。代表聚离子线性特性的参数(包括单体浓度的替代方法)至少在低浓度下即可显示等效链的一般行为。在高浓度下,局部相互作用变得很重要,模型的确切细节也变得很重要。还讨论了添加盐的影响,一个结论是,经验加和法则,分别处理聚电解质和任何盐的贡献,是一个合理的近似值,这证明了无盐溶液的研究是合理的。非单调行为可以更好地描述为有限大小效应和双层效应的组合。代表聚离子线性特性的参数(包括单体浓度的替代方法)至少在低浓度下即可显示等效链的一般行为。在高浓度下,局部相互作用变得很重要,模型的确切细节也变得很重要。还讨论了添加盐的影响,一个结论是,经验加和法则,分别处理聚电解质和任何盐的贡献,是一个合理的近似值,这证明了无盐溶液的研究是合理的。非单调行为可以更好地描述为有限大小效应和双层效应的组合。代表聚离子线性特性的参数(包括单体浓度的替代方法)至少在低浓度下即可显示等效链的一般行为。在高浓度下,局部相互作用变得很重要,模型的确切细节也变得很重要。还讨论了添加盐的影响,并得出的结论是,经验加和法则(分别处理聚电解质和任何盐的贡献)是一个合理的近似值,这证明了无盐溶液的研究是合理的。包括单体浓度的替代物在内,至少在低浓度下,它有可能表现出等效链的一般行为。在高浓度下,局部相互作用变得很重要,模型的确切细节也变得很重要。还讨论了添加盐的影响,并得出的结论是,经验加和法则(分别处理聚电解质和任何盐的贡献)是一个合理的近似值,这证明了无盐溶液的研究是合理的。包括单体浓度的替代选择在内,至少在低浓度下,它有可能表现出等效链的一般行为。在高浓度下,局部相互作用变得很重要,模型的确切细节也变得很重要。还讨论了添加盐的影响,一个结论是,经验加和法则,分别处理聚电解质和任何盐的贡献,是一个合理的近似值,这证明了无盐溶液的研究是合理的。
更新日期:2018-06-22
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