The collapse of polyelectrolyte brushes made of 4-arm stars mediated by trivalent salt counterions

ABSTRACT

Langevin dynamics (LD) simulations were conducted to study the collapse of polyelectrolyte brushes made of 4-arm stars induced by trivalent salt counterions. Consistent with previous studies of the collapse of fully charged linear polymer brushes in the presence of trivalent salt counterions, the electrostatic bridging of grafted star chains by trivalent salt counterions plays a critical role in the bundle formation. In sharp contrast to the dominant probability of inter-chain bridging between a trivalent salt ion and multiple charged monomers from different chains in the collapse of polyelectrolyte brushes made of fully charged linear chains, the probability of intra-chain bridging was found to be much larger than that of inter-chain bridging for the collapse of fully charged star brushes due to the topological structure. The average number of bound charged monomers per trivalent salt counterion decreases drastically with decreasing charge fraction of grafted star chains. The ability of a trivalent salt counterion to bind with three or more charged monomers is greatly enhanced by increasing Bjerrum length. The probability of inter-chain bridging mode increases with increasing Bjerrum length. The larger Bjerrum length is, the smaller the bundle size and the tighter binding of the chains inside a bundle will become.

KEYWORDS:

• Polyelectrolyte brushes
• molecular simulation
• multivalent counterion
• electrostatic bridging

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors thank the financial supports from the National Natural Science Foundation of China (NSFC project 21774067). C. T. acknowledges the support from K. C. Wong Magna Fund in Ningbo University.