Folding of a single polymer chain and phase transition  

作　　者：DING YanWei ZHANG GuangZhao 

机构地区：[1]Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science andTechnology of China, Hefei 230026, China

出　　处：《Chinese Science Bulletin》2009年第11期1908-1911,共4页

基　　金：Supported by the National Natural Science Funds for Distinguished Young Scholar (Grant No. 20474060);Major State Basic Research Development Program of China (Grant No. 2007CB936401)

摘　　要：Using an ultra-sensitive differential scanning calorimetry (US-DSC), we have investigated the folding and aggregation behaviors of poly(N-isopropylacrylamide) (PNIPAM) chains in dilute and semidilute solutions. In the heating process, the intrachain folding and interchain aggregation simultaneously occur in the dilute solutions, and the ratio of intrachain folding increases with decreasing concentra-tion. In the semidilute solutions, PNIPAM chains show limited interchain aggregation with elevated temperature, because most of the PNIPAM chains have been collapsed at lower temperature. In an ex-tremely dilute solution, PNIPAM chains undergo a single folding transition in the heating process. By extrapolating heating rate and concentration to zero, we have obtained the phase transition tempera-ture (TS) and enthalpy change (△HS) of the single chain folding. △HS is higher than that for a phase transition involving intrachain collapse and interchain aggregation, indicating that a single chain fold-ing can not be taken to be a macroscopic phase transition.Using an ultra-sensitive differential scanning calorimetry （US-DSC）, we have investigated the folding and aggregation behaviors of poly（N-isopropylacrylamide） （PNIPAM） chains in dilute and semidilute solutions. In the heating process, the intrachain folding and interchain aggregation simultaneously occur in the dilute solutions, and the ratio of intrachain folding increases with decreasing concentra- tion. In the semidilute solutions, PNIPAM chains show limited interchain aggregation with elevated temperature, because most of the PNIPAM chains have been collapsed at lower temperature. In an ex- tremely dilute solution, PNIPAM chains undergo a single folding transition in the heating process. By extrapolating heating rate and concentration to zero, we have obtained the phase transition tempera- ture （Ts） and enthalpy change （Arts） of the single chain folding. AHs is higher than that for a phase transition involving intrachain collapse and interchain aggregation, indicating that a single chain fold- ing can not be taken to be a macroscopic phase transition.

关 键 词：高分子链 相变温度 折叠法 PNIPAM 异丙基丙烯酰胺 聚集行为 差示扫描量热 加热过程 

分 类 号：O631.12[理学—高分子化学] TG139.6[理学—化学]