Interaction between like-charged polyelectrolyte-colloid complexes in electrolyte solutions: a Monte Carlo simulation study in the Debye-Hückel approximation.
Interaction between like-charged polyelectrolyte-colloid complexes in electrolyte solutions: a Monte Carlo simulation study in the Debye-Hückel approximation.
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DOI：
10.1063/1.3459125
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发表时间：
2010-05
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影响因子：
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通讯作者：
Domenico Truzzolillo;F. Bordi;Francesco Sciortino;S. Sennato
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文献类型：
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作者：
Domenico Truzzolillo;F. Bordi;Francesco Sciortino;S. Sennato
我们研究了不同电荷的聚电解质-胶体复合物在电解质溶液中的有效相互作用，通过Monte Carlo模拟。当短而灵活的双链吸附到分散在电解质溶液中的带相反电荷的胶体球上时，形成这些复合物。在我们的模拟中，与静电能相比，相邻单体之间的弯曲能很小，并且链一旦被吸附，就不与溶液交换，尽管它们在颗粒表面上重新排列以容纳进一步的吸附链或由于与相邻复合物的静电相互作用。出乎意料的是，当两个相互作用的粒子彼此接近时，表面电荷分布的重新排列总是产生反平行的偶极双峰，它们在等电点处的方向反转。这些发现清楚地排除了偶极-偶极相互作用对所观察到的复合物之间的吸引力相互作用的贡献，指出这种悬浮液不能被认为是偶极流体。在改变电解质的离子强度时，我们发现，为了观察由于电荷在其表面上的不均匀分布而引起的带相同电荷的复合物之间的吸引（“斑块吸引”），需要与胶体颗粒的尺寸相比较短的屏蔽长度kappa（-1）。另一方面，通过改变电荷/粒子电荷比Xi（s），在短间隔下，带相同电荷的聚电解质修饰的粒子之间的相互作用从纯粹的排斥演化为强烈的吸引。因此，复合物之间的有效相互作用的特征在于势垒，其高度取决于净电荷和它们的表面电荷分布的不均匀性。
We study the effective interaction between differently charged polyelectrolyte-colloid complexes in electrolyte solutions via Monte Carlo simulations. These complexes are formed when short and flexible polyelectrolyte chains adsorb onto oppositely charged colloidal spheres, dispersed in an electrolyte solution. In our simulations the bending energy between adjacent monomers is small compared to the electrostatic energy, and the chains, once adsorbed, do not exchange with the solution, although they rearrange on the particles surface to accommodate further adsorbing chains or due to the electrostatic interaction with neighbor complexes. Rather unexpectedly, when two interacting particles approach each other, the rearrangement of the surface charge distribution invariably produces antiparallel dipolar doublets that invert their orientation at the isoelectric point. These findings clearly rule out a contribution of dipole-dipole interactions to the observed attractive interaction between the complexes, pointing out that such suspensions cannot be considered dipolar fluids. On varying the ionic strength of the electrolyte, we find that a screening length kappa(-1), short compared with the size of the colloidal particles, is required in order to observe the attraction between like-charged complexes due to the nonuniform distribution of the electric charge on their surface ("patch attraction"). On the other hand, by changing the polyelectrolyte/particle charge ratio xi(s), the interaction between like-charged polyelectrolyte-decorated particles, at short separations, evolves from purely repulsive to strongly attractive. Hence, the effective interaction between the complexes is characterized by a potential barrier, whose height depends on the net charge and on the nonuniformity of their surface charge distribution.