Mechanical properties of reversibly cross-linked ultrathin polyelectrolyte complexes.

Tensile properties of microcoupons of polyelectrolyte complex, formed by the multilayering method, were determined using a micromechanical analysis system. The degree of internal ion-pair ("electrostatic") cross-linking was reversibly controlled by exposure to salt solution of varying concentration, which "doped" counterions into the films, breaking polymer/polymer ion pairs in the process. Linear stress-strain behavior was observed for a poly(styrene sulfonate)/poly(diallyldimethylammonium) multilayer up to 2% deformation. The dependence of modulus on cross-link density could be rationalized well by classical theories of rubber elasticity, including some insight on the topology of polyelectrolyte complexes.