Colloidlike behaviour of a polystyrene-b-poly(ethylene-co-propylene) diblock copolymer dissolved in n-decane investigated by pulsed field gradient nuclear magnetic resonance

The self-diffusion of a polystyrene-b-poly(ethylene-co-propylene) diblock c opolymer dissolved in a preferential solvent for the aliphatic block, n-dec ane, was investigated by pulsed field gradient NMR. The diblock copolymer f orms micelles in solution, the structure of the solid polymer being preserv ed in the native solution because the polystyrene is in the glassy state. T he equilibrium state is attained upon heating which again freezes in upon c ooling to room temperature. The hydrodynamic radius of the micelles decreas es by about 50% during this heating-cooling process. The concentration depe ndence of the self-diffusivity shows typical colloidlike behaviour, and it can be described by a Vogel-Fulcher-Tamwann-like equation. No indications o f crystallization at higher concentrations are observed in the micellar sol ution because the micellar sizes are slightly polydisperse. The self-diffus ivity was measured up to the glasslike state, where in-cage-diffusion and d ynamic heterogeneities could be detected.