Adroher-Benítez Irene, Martín-Molina Alberto, Ahualli Silvia, Quesada-Pérez Manuel, Odriozola Gerardo, Moncho-Jordá Arturo
Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva S/N, 18001 Granada, Spain.
Departamento de Física, Escuela Politécnica Superior de Linares, Universidad de Jaeén, 23700 Linares, Jaeén, Spain.
Phys Chem Chem Phys. 2017 Mar 1;19(9):6838-6848. doi: 10.1039/c6cp08683g.
In this work the equilibrium distribution of ions around a thermo-responsive charged nanogel particle in an electrolyte aqueous suspension is explored using coarse-grained Monte Carlo computer simulations and the Ornstein-Zernike integral equation theory. We explicitly consider the ionic size in both methods and study the interplay between electrostatic and excluded-volume effects for swollen and shrunken nanogels, monovalent and trivalent counterions, and for two different nanogel charges. We find good quantitative agreement between the ionic density profiles obtained using both methods when the excluded repulsive force exerted by the cross-linked polymer network is taken into account. For the shrunken conformation, the electrostatic repulsion between the charged groups provokes a heterogeneous polymer density profile, leading to a nanogel structure with an internal low density hole surrounded by a dense corona. The results show that the excluded-volume repulsion strongly hinders the ion permeation for shrunken nanogels, where volume exclusion is able to significantly reduce the concentration of counterions in the more dense regions of the nanogel. In general, we demonstrate that the thermosensitive behaviour of nanogels, as well as their internal structure, is strongly influenced by the valence of the counterions and also by the charge of the particles. On the one hand, an increase of the counterion valence moves the swelling transition to lower temperatures, and induces a major structuring of the charged monomers into internal and external layers around the crown for shrunken nanogels. On the other hand, increasing the particle charge shifts the swelling curve to larger values of the effective radius of the nanogel.
在这项工作中，我们使用粗粒化蒙特卡罗计算机模拟和奥恩斯坦-泽尔尼克积分方程理论，探索了电解质水悬浮液中热响应性带电纳米凝胶颗粒周围离子的平衡分布。我们在两种方法中都明确考虑了离子大小，并研究了溶胀和收缩的纳米凝胶、单价和三价抗衡离子以及两种不同纳米凝胶电荷情况下静电和排除体积效应之间的相互作用。当考虑交联聚合物网络施加的排除排斥力时，我们发现两种方法获得的离子密度分布之间具有良好的定量一致性。对于收缩构象，带电基团之间的静电排斥引发了聚合物密度分布的不均匀性，导致纳米凝胶结构内部有一个低密度孔，周围是致密的电晕。结果表明，排除体积排斥强烈阻碍了收缩纳米凝胶的离子渗透，其中体积排除能够显著降低纳米凝胶更致密区域中抗衡离子的浓度。总体而言，我们证明了纳米凝胶的热敏行为及其内部结构受到抗衡离子价态以及颗粒电荷的强烈影响。一方面，抗衡离子价态的增加将溶胀转变温度降低，并导致收缩纳米凝胶的带电单体在冠层周围形成内部和外部层的主要结构。另一方面，增加颗粒电荷会使溶胀曲线向纳米凝胶有效半径的更大值移动。
