The effects of heating rate on the aggregate behavior of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) in aqueous solutions were investigated in detail by laser light scattering and TEM. By employing two separate heating protocols

step-by-step heating at 5 K/step and one-step jump

to heat the sample from 15oC to the selected temperature

we found that the heating rate only showed significant effect on the aggregates above the cloud point. The aggregate formed by step-by-step heating exhibited a much larger size and a broader size distribution than those formed by one-step jump heating. Moreover

neither of the aggregates were ideal micellar structures as indicated by the size and the Rg/Rh values. On the contrary

at temperatures below the cloud point where the block copolymer formed core-shelled micelles

the heating rate showed negligible effect on the size and size distribution of the micelles. Since the system underwent a phase separation above the cloud point

the heating rate effect could be reasonably explained by the phase separation mechanisms: the nucleation-and-growth mechanism in the metastable region and the spinodal decomposition mechanism in the unstable region.