Polyelektrolyte

Polyelektrolyte, or polyelectrolyte, refers to a polymer bearing multiple ionizable groups along its chain that can dissociate in polar solvents to yield charged repeating units and mobile counterions. Depending on the sign of the charge, polyelectrolytes are classified as polycations (positively charged) or polyanions (negatively charged); there are also polyzwitterionic types that carry both charges within the same molecule. Common charged groups include carboxylates and sulfonates (anionic) or quaternary ammonium groups (cationic). Natural examples include DNA, RNA, and many proteins; synthetic examples include polystyrene sulfonate and various polyacrylates or polydiallyldimethylammonium polymers.

In solution, electrostatic interactions along the chain and with counterions influence conformation and dynamics, often leading to expanded structures at low salt and collapsed states at high salt or extreme pH. The properties of polyelectrolytes are highly sensitive to ionic strength, pH, and counterion binding, as described by concepts such as counterion condensation and Manning theory. They readily form complexes with oppositely charged polymers, yielding polyelectrolyte complexes and coacervates that can precipitate, gel, or encapsulate materials.

Applications are broad and include water treatment, soil conditioning, rheology modification, and flocculation; were used as dispersants and superplasticizers; and play roles in drug and gene delivery, biomedical coatings, sensors, and advanced materials. Preparation methods involve polymerization of charged monomers or post-polymerization modification to introduce or adjust ionizable groups.