Competitive solvation effects in polyelectrolyte solutions
Alexandros Chremos, Jack F. Douglas
An understanding of the solution properties and phase behavior of natural and synthetic polyelectrolytes requires an understanding of the competitive association of water (hydration) and ion association to the polymer backbone and the consequences of large scale clustering of counter-ions around highly charged polymers and associated chain clustering due to the high polarizability of this diffuse counter-ion cloud. We investigate the influence of counter-ion affinity for polyelectrolyte segments on the conformational properties of individual highly charged flexible polyelectrolyte chain using molecular dynamics simulations that include both ions and an explicit solvent. We find that an increase in the affinity of the counter-ions for polyelectrolyte segments leads to a significant increase in the average number of interfacial counter-ions. For a constant charge interaction defined by a fixed Bjerrum length and Debye screening length, this increase in the number of interfacial counter-ions with an increased strength in counter-ion affinity for the polyelectrolyte segments decreases the size of the polyelectrolyte chain and the average polyelectrolyte shape becomes less extended. We also calculate and quantify the distribution of counter-ions around solvated polyelectrolyte chains, where we find that a strong affinity of the counter-ions for the polyelectrolyte segments results in a decrease in the spatial extent of the diffuse counter-ion cloud around highly charged polymers.