Conformation and phase diagrams of flexible polyelectrolytes

The present article addresses the dilute solution behavior of two different polyelectrolyte systems: Aqueous solutions of quaternized poly(2-vinylpyridines) and of polyacrylic acids. Firstly, it is demonstrated that the dimensions of the chains for all investigated polyelectrolytes are described by a model that explicitly considers (i) an excluded volume comprising contributions of the electrostatic interactions via the effective charge density, and (ii) the intrinsic excluded volume in terms of the Flory interaction parameter. The effect of the chain hydrophobicity and the type of counterions on the coil dimension of the chains and the effective charge density is discussed. The latter is compared with results obtained from osmotic pressure measurements and conductometry. The second part of the review is devoted to an investigation of the phase behavior of the two systems. For quaternized poly-2-vinylpyridines phase transitions are induced by addition of inert salt, typically NaI and are denoted as "salting out" and "salting in". The phase behavior is assumed not to be influenced by ion specific interactions other than the Flory excluded volume parameter. Contrary, in case of polyacrylic acid highly specific interactions, such as complexation, between the polyion and bivalent earth alkaline cations may cause a precipitation of the polyelectrolyte. The precipitation point depends on both, the concentration of the polyions and the counter ions. investigation of the coil dimensions by means of combined static and dynamic light scattering reveals a coil collapse towards spherical particles. Possible transition states along this shrinking process are discussed.