The Ionic Environment of Rod-like Polyelectrolytes
Association between electrolyte ions and polyions is of fundamental importance. Here, we discuss the nature of the distribution of small ions around polyelectrolytes and examine the sensitivity of the distribution to salt concentration and polyion charge density. Two polyion models are considered, namely, a simplified one in which the polyion is taken to be a uniformly charged cylinder and an atomically more detailed one in which the smaller ions interact with the polyion on an atom by atom basis. The hypernetted chain integral equation and Monte Carlo computer experiments are used to develop the results for ionic distributions. The results confirm that the ionic environment around highly charged polyions is relatively insensitive to large changes in bulk electrolyte concentrations in the case of the simpler model of the polyion. Further, the concept of an effective net charge for the polyion as a determinant for the asymptotic electrostatic potential holds. The results for the more detailed model of the polyion indicate that charge association can be understood qualitatively using the simpler, uniformly charged model. Such a simplification is, however, not sufficient for determining the local ionic concentrations and the spatial extent of the association quantitatively.
KeywordsEntropy Hydrate Rubber
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