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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 15℃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 R_g/R_h 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.
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 15 ° C to the selected temperature, we found that the heating rate only showed significant effect on the aggregates above the cloud point. aggregate accumulated by step-by -step heating promotes 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 R_g / R_h values. Now 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 .ince the system underwent a phase separation above the cloud point, the heating rate effecrs t 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.