EFFECT OF HEATING RATE ON THERMO-INDUCED AGGREGATION OF POLY(ETHYLENE OXIDE)-B-POLY(N-ISOPROPYLACRYL

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.="" 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.="">