Conformational transition of tethered poly(N-isopropylacrylamide) chains in coronas of micelles and vesicles

Thermosensitive micelles and vesicles in water were prepared using narrowly distributed polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) diblock copolymers. and the conformational changes of PNIPAM blocks in the coronas of micelles and vesicles were investigated by a combination of static and dynamic laser light scattering. Our results reveal that PNIPAM chains forming brushes in the corona of the micelles undergo a continuous collapse transition, which is consistent with the theoretical predictions. PNIPAM brushes in the coronas of the vesicles exhibit a broad transition from 28 to 36 degreesC with a shrinking in the range 20-28 degreesC. The shrinking at a low temperature is attributed to the interchain overlapping of the dense brushes on the concave surface of the vesicle. On the other hand. the vesicles become hollow with temperature increasing because of the collapse of the chains in the inside corona of the vesicle.