Polyelectrolyte-Macroion Complexation in 1:1 and 3:1 Salt Contents: A Brownian Dynamics Study

J Yang and R Ni and DP Cao and WC Wang, JOURNAL OF PHYSICAL CHEMISTRY B, 112, 16505-16516 (2008).

DOI: 10.1021/jp807596v

On the basis of the coarse-grained model, we performed Brownian dynamics simulations to investigate behavior of the polyelectrolyte (PE)-macroion complexations in 1:1 and 3:1 salt contents. Our simulation results show that in 3:1 salt content there exists a critical salt concentration (CSC), which is determined by the charge stoichiometry, for the breakup of the PE-macroion complexations. Beyond the CSC concentration, an obvious depletion appears in the macroion-macroion and macroion-PE interactions, which is absent in 1: 1 salt content. Both the mobilities of macroions and PEs increase monotonically with increasing the salt concentration in 1: 1 and 3:1 salt contents. And the mobility in 3:1 salt content is always larger than that in corresponding 1: 1 salt content, which is due to the fact that in 3:1 salt content the PE- macroion complexations are looser than those in 1: 1 salt content. Moreover, we observed the collapse and re-expansion of PE chains with the increase of the salt concentration in the PEs-macroions systems of 3:1 salt content, which is due to the charge inversion of PE chains induced by the adsorption of trivalent cations In addition, we also explored the effects of salt concentration and the length and charge density of PE chains. Our simulation results show that the effects of the length and charge density of PE chains in both salt contents on the radial distribution functions (RDFs) between macroions and between a macroion and a PE segment are similar to these in salt free solution basically. However, we observed an interesting phenomenon that the gyration radius of PE chains in the system of 3:1 salt content is not affected significantly by its charge density, while that in 1: 1 salt content increases monotonically.

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