polyelectrolytes

Polyelectrolytes are polymers that contain ionizable groups which dissociate in polar solvents, causing the polymer chain to carry multiple charges. Depending on the ionizable groups, polyelectrolytes can be polycations or polyanions. They include synthetic polymers such as polystyrene sulfonate, polyacrylic acid, and poly(diallyl dimethylammonium chloride), as well as natural polyelectrolytes like DNA, alginate, and chitosan.

Their charged backbones attract counterions, leading to strong electrostatic interactions, extended chain conformations at low ionic strength, and sensitivity to pH and salt concentration. Phenomena such as counterion condensation and Manning theory describe charge screening. The osmotic pressure of counterions and the high charge density influence viscosity, diffusion, and rheology.

They readily form complexes with oppositely charged polymers, producing polyelectrolyte complexes and multilayer films via layer-by-layer assembly, enabling coatings, packaging, and drug delivery. In water treatment they act as flocculants; in personal care they serve as thickeners and stabilizers; in biotechnology they support gene delivery and hydrogel formation.

Synthesis and characterization: polyelectrolytes are prepared by polymerizing charged monomers or by post-polymerization functionalization. Charge density and distribution, molecular weight, and chain conformation govern properties; characterization uses intrinsic viscosity, light scattering, osmotic pressure, and spectroscopic methods.