The effects of grafting density and charge fraction on the properties of ring polyelectrolyte brushes: a molecular dynamics simulation study

Abstract

Using molecular dynamics simulations, the flexible ring polyelectrolyte chains tethered to a planar substrate and immersed in good solvents are investigated systematically. Two sets of simulations are performed to explore the effects of grafting density and charge fraction, respectively. Both the monovalent and trivalent counterions are considered. The height of the brush H follows a scaling relation with grafting density (~σgν) and charge fraction (~fν). The values of the exponents are different from those of the linear counterparts. Through a careful analysis on the distributions of monomers and counterions, pair correlation functions of monomer-monomer and monomer-counterion, as well as the fractions of trivalent counterions in four states, the equilibrium structures of the ring PE brushes are examined in detail. Furthermore, a brief comparison with the ‘equivalent’ linear brush is carried out. Also, our results can serve as a guide for improving the performance of ring polyelectrolyte brushes as unique surface modifiers.