Complexation of a polyelectrolyte with oppositely charged spherical macroions: Giant inversion of charge

Abstract

Complexation of a long flexible polyelectrolyte (PE) molecule with oppositely charged spherical particles such as colloids, micelles, or globular proteins in a salty water solution is studied. PE binds spheres winding around them, while spheres repel each other and form almost periodic necklace. If the total charge of PE in the solution is larger than total charge of spheres, repulsive correlations of PE turns on a sphere lead to inversion of the net charge of each sphere. In the opposite case when the total charge of spheres is larger, we predict another correlation effect; spheres bind to the PE in such a great number that they invert the charge of the PE. The inverted charge by absolute value can be larger than the bare charge of PE even when screening by monovalent salt is weak. At larger concentrations of monovalent salt, the inverted charge can reach giant proportions. Near the isoelectric point where total charges of spheres and PE are equal, necklaces condense into macroscopic bundles. Our theory is in qualitative agreement with recent experiments on micelles–PE systems.