The collapse transition and the segmental dynamics in concentrated micellar solutions of P(S-b-NIPAM) diblock copolymers
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We investigate concentrated solutions of poly(styrene-b-N-isopropyl acrylamide) (P(S-b-NIPAM)) diblock copolymers in deuterated water (D2O). Both structural changes and the changes of the segmental dynamics occurring upon heating through the lower critical solution temperature (LCST) of PNIPAM are studied using small-angle neutron scattering and neutron spin-echo spectroscopy. The collapse of the micellar shell and the cluster formation of collapsed micelles at the LCST as well as an increase of the segmental diffusion coefficient after crossing the LCST are detected. Comparing to our recent results on a triblock copolymer P(S-b-NIPAM-b-S) , we observe that the collapse transition of P(S-b-NIPAM) is more complex and that the PNIPAM segmental dynamics are faster than in P(S-b-NIPAM-b-S).