A self-diffusion study in aqueous solution and lyotropic mesophases of amphiphilic block copolymers

Water-soluble poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxid e) (PEO-PPO-PPO) triblock copolymers are high-molecular-weight nonionic cop olymers and form micellar solutions and liquid-crystalline mesophases in wa ter. We studied the temperature dependence of polymer and water self-diffus ion in solutions and lyotropic mesophases of the PEO13 PPO30 PEO13/water an d PEO21 PPO47 PEO21/water binary systems. The self-diffusion measurements w ere performed by means of the pulsed field gradient spin-echo NMR method. T he analysis of the water mobility was realised using "the obstruction facto r" and "the two-site model", which consider the reduction of the water self -diffusion due to the microstructure of the lyotropic aggregates and to the presence of one part of the solvent bound to the polymer aggregate surface s. We calculated the water obstruction factors and the hydration numbers as a function both of the polymer composition and of the temperature. The res ults are compared with the data obtained in mesophases formed by classical surfactants.