The collapse transition of poly(styrene-b-(N-isopropyl acrylamide)) diblock copolymers in aqueous solution and in thin films

The thermal behavior of a poly(styrene-b-N-isopropyl acrylamide) diblock copolymer was studied in aqueous solution as well as in thick and in thin films. The polymer was synthesized using reversible addition-fragmentation chain transfer. The critical micelle concentration in aqueous solution was determined using fluorescence correlation spectroscopy. The lower critical solution temperature (LCST) of micellar solutions was detected using microcalorimetry and turbidimetry at 31 degrees C. Using dynamic light scattering, the collapse of the micelles at the LCST as well as their clustering above was observed. These findings were corroborated with small-angle X-ray scattering. In thick films immersed in water, similar findings were made. In a thin film, however, the LCST is depressed and is found at 26-27 degrees C.