Abstract
We numerically investigate the behaviors of polyelectrolyte chains in solvent mixtures, taking into account the effects of the concentration inhomogeneity and the degree of the ionization. When changing the interaction parameters between the solvent components, we found a first order transition of the polymer conformation. In the mixing state far from the coexistence curve, the polymers behave as semi-flexible chains. In the phase-separated state, on the other hand, they show compact conformations included in the droplets. As the interaction parameters of the mixture are increased, an inhomogeneous concentration field develops around the polymer and induces critical Casimir attractive interactions among the monomers. The competition between the electrostatic interactions and the critical Casimir ones gives rise to drastic changes in the conformation.
Highlights
Polyelectrolytes play important roles in many systems from biology to industry
We numerically studied the conformations of polyelectrolytes in solvent mixtures
We take into account the electrostatic interaction, the effective interaction induced by the concentration inhomogeneity and the ionization degree, simultaneously
Summary
Polyelectrolytes play important roles in many systems from biology to industry. Since the conformations of polyelectrolytes affect their physical and biological properties, they have been intensively studied.[1,2,3,4,5,6] In comparison to electrically neutral polymers, polyelectrolytes are more rigid because of long-range electrostatic interactions among the monomers.[7,8] They tend to behave like rod or semi-flexible polymers in good or theta solvents. On the other hand, effective attractive interactions work among the monomers. There, the concentration inhomogeneity in the solvent mixture induces effective attractive interactions among the monomers. There are only a few studies which consider the effects of the concentration inhomogeneity on the polyelectrolytes.[27,35] To our knowledge, there is no study which considers both the contributions from the electrostatic interactions and the concentration inhomogeneity to the polymer conformation, in spite of their importance. We study the behaviors of polyelectrolytes in solvent mixtures by means of fluid particle dynamics simulation with a bead-spring model.[37,38,39] In particular, we focus on the effects of the ionization degree and the attractive interactions, caused by the concentration inhomogeneity, on the conformation of the. The ionization degree and the affinity between the colloid and the solvent depend on the interaction parameters between the solvent components
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