Thermoresponsive aggregation of PS–PNIPAM–PS triblock copolymer: A combined study of light scattering and small angle neutron scattering

• We studied polystyrene–b-poly(N-isopropylacrylamide)–b-polystyrene in water.
• Small angle neutron scattering shows a 3-level hierarchical morphology.
• Large clusters densify upon the thermal transition of poly(N-isopropylacrylamide).
• Intermicellar aggregates shrink upon this thermal transition.
• Light scattering supports the small angle neutron scattering results.

The aggregate structure of a thermoresponsive polystyrene–b-poly(N-isopropylacrylamide)–b-polystyrene (PS–PNIPAM–PS) triblock copolymer was investigated as a function of temperature in aqueous solutions by the combination of small angle neutron scattering (SANS) and dynamic/static light scattering (LS). SANS shows that the system consists of spherical intermicellar aggregates which self-assemble into larger clusters either at temperatures below or above the lower critical solution temperature (LCST). Upon the solubility transition of PNIPAM the mass of the clusters increases significantly, whereas their size remains constant and the size of the intermicellar aggregates decreases. This picture is consistent with the LS data where the signature of the two entities in solution is observed. The combination of LS and SANS studies has presented a clearer scenario on the thermoresponsive aggregation behavior of the investigated PS–PNIPAM–PS triblock copolymer.

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