WEAKLY CHARGED POLYELECTROLYTES IN A POOR SOLVENT

We show that a weakly charged polyelectrolyte in a salt free poor solvent undergoes a mesophase separation transition by lowering the temperature. This transition is investigated at low temperature by studying the possibility of micelle formation and at higher temperature by studying the divergence of the peak at finite wave vector of the polymer-polymer correlation function. As salt is added to the solution, the peak in the structure factor disappears and the transition becomes a usual demixing phase separation between polymer and solvent. The multicritical point of these two transitions is a so-called Lifshitz point; in the vicinity of this point a Ginzburg criterion shows that concentration fluctuations play an important role and that the mean field theory is not sufficient. At higher salt concentration the demixing transition belongs to the Ising universality class. Finally, we discuss the behavior of solutions containing both weakly charged and neutral polymers: here also the peak in the structure factor disappears as the concentration of neutral polymers is increased.