Flexible polyelectrolyte conformation in the presence of cationic and anionic surfactants

In this work we have studied the conformation of flexible polyelectrolyte chains in the presence of cationic and anionic surfactant molecules. We developed a simple theoretical model for the formation of the polyelectrolyte–cationic surfactant complexes and mixed micelles formed by cationic and anionic surfactant molecules, in the framework of the Debye–Hückel–Bjerrum–Manning and Flory theories, with the hydrophobic interaction included explicitly as an effective short-ranged attraction between the surfactant hydrocarbon tails. This simple model allows us to calculate the extension of the polyelectrolyte–cationic surfactant complexes as a function of the anionic surfactant concentration, for different types of cationic and anionic surfactant molecules. A discrete conformational transition from a collapsed state to an elongated coil was found, for all surfactant chain lengths we have considered, in agreement with the experimental observations for the unfolding of ​DNA–cationic surfactant complexes.