| Abstract
| - The dynamic structure factor S(q,t) of seven diblock copolymers in a common solvent wasmeasured by photon correlation spectroscopy as a function of concentration (φ) in the disordered statenear the disordered-to-order transition (ODT). Both symmetric and asymmetric diblock copolymers ofstyrene-b-isoprene (SI) with molecular masses ranging from 0.95 to 3.6 million g/mol and theirhydrogenated styrene-b-(ethylene-alt-propylene) (SEP) counterparts have been considered. The maximumof the static structure factor S(q*) and the characteristic spacing 1/q* do not conform to theoreticalpredictions over the whole φ range up to φODT. The S(q,t) is determined mainly by the relative contributionof two relaxation processes one of which is diffusive (q2-dependent rate). When composition fluctuationcorrections become important for S(q*) at φx< φODT, S(q,t) exhibits a dynamic crossover from a dominantpure relaxational (q-independent rate) to a dominant diffusive character. This new dynamic behavior inthe shape of S(q,t) of narrowly distributed diblock copolymer solutions is captured theoretically. Aboveabout φx, the self-diffusion coefficient Ds(φ) obtained from the S(q,t) at low q/q* values becomesthermodynamically retarded. The real phase morphology of diblock copolymers is well complemented bytheir dynamic structure.
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