Molecular exchange in ordered diblock copolymer micelles

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Molecular exchange kinetics of diblock copolymers forming spherical micelles packed on a body-centered cubic (bcc) lattice were investigated using time-resolved small-angle neutron scattering (TR-SANS). Ordered arrays of polystyrene spheres were prepared by mixing 15 vol % poly(styrene-b-ethylene- alt-propylene) (PS-PEP) in squalane, a highly selective solvent for the PEP block. Two pairs of diblock copolymers were examined, characterized by two different PS core block molecular weights (〈MPS〉 = 26500 and 42800). Each pair contained two nearly identical diblock copolymers, one with a deuterated PS block (dPS-PEP) and the other with a protonated PS block (hPS-PEP). Protonated and deuterated squalane were blended to achieve a contrast-matched condition with uniformly mixed dPS and hPS (50/50 by volume) core chains. Beginning with a statistically random array of pure dPS and hPS cores distributed on the bcc lattice, molecular exchange was monitored at multiple temperatures by TR-SANS. Exchange of deuterated and protonated chains results in a decay in SANS intensity, which yields a kinetic function revealing a broad spectrum of relaxation times. These results are qualitatively consistent with our previously reported findings for molecular exchange between PS-PEP micelles in a dilute (1 vol %) squalane solution. However, the measured characteristic time constant for the concentrated, ordered system is more than an order of magnitude slower than in the dilute, disordered dispersion.

Original languageEnglish (US)
Pages (from-to)3594-3604
Number of pages11
Issue number9
StatePublished - May 10 2011


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