The critical onset of counterion condensation: A survey of its experimental and theoretical basis

A survey of experimental and theoretical investigations into the condensation of counterions on polyelectrolyte chains above a critical threshold of polymer charge density is presented. Current models contain critical formation of a condensed layer that cannot be diluted off the polymer but differ qualitatively in their description of the structure of the layer. A documented position is taken that the model of a line of discrete charges is more realistic than a uniformly charged cylinder. The question of attractive electrostatic interactions between identically charged polymers is addressed.