THEORY OF COLLAPSE OF POLYELECTROLYTE NETWORKS IN SOLUTIONS OF IONOGENIC SURFACTANTS

The simplest theory of swelling and collapse of slightly charged polyelectrolyte networks in solutions of ionogenic micelle-forming surfactants having the charge opposite to the network charge is proposed. In the free energy of the system both contributions of the energy of network units interaction, micelle-formation energy and elastic energy of the network strain and those related with translational entropy of various ions present in the system are taken into account. Depending on the surfactant molecules concentration c0 one of three regimes of the network behavior is realized. For small c0 micelles inside a network don't form, and a network swells as in solution of low-molecular salt. For c0 = c* the surfactant concentration inside a network exceeds the critical concentration of micelle-formation, micelles are formed, as a result the osmotic pressure of surfactant ions decreases and the collapse of a network is observed. Above the second critical concentration c** the further increase of the number of micelles in a network ends and the network dimensions attain those of the uncharged network. Theoretical results correspond to experimental data obtained earlier.