Associating polyelectrolytes: From hydrophobic microdomain formation to rheological control of aqueous dispersions

The aqueous solution properties have been studied of comb-like copolymers whose main chain is a polyelectrolyte [poly(acrylic acid)] and the grafts are water insoluble moieties [alkyl chains, polyethylene oxide residues above their lower critical solution temperature (LCST)]. Under appropriate experimental conditions the hydrophobic residues form small aggregates which act as junction zones between the chains and impart the reversible gel-like character to the system. The effect of several experimental parameters has been discussed. An increase in the size or in the grafting density of alkyl chains induces a stronger thickening or gelling tendency in the system. The same behavior is observed after the ionic strength has been increased or amphiphilic species such as surfactant or globular proteins have been added. When the grafts are chains with a LCST, reversible thermothickening systems are obtained.