Conformational Transition of Poly(N-isopropylacrylamide) Single Chains in Its Cononsolvency Process: A Study by Fluorescence Correlation Spectroscopy and Scaling Analysis

详细信息    查看全文

• 作者：Fei Wang ; Yi Shi ; Shuangjiang Luo ; Yongming Chen ; Jiang Zhao
• 刊名：Macromolecules
• 出版年：2012
• 出版时间：November 27, 2012
• 年：2012
• 卷：45
• 期：22
• 页码：9196-9204
• 全文大小：414K
• 年卷期：v.45,no.22(November 27, 2012)
• ISSN：1520-5835

文摘

Fluorescence correlation spectroscopy (FCS) has been adopted to investigate the conformational transition of poly(N-isopropylacrylamide) (PNIPAM) single chains with moderate molecular weights in the cononsolvency process. A practical approach of performing accurate FCS measurements with the presence of the refractive index mismatch was developed. The practical and reliable FCS calibration facilitates the acquisition of the hydrodynamic radius (R_H) of PNIPAM single chains with the change of the water鈥揺thanol composition. By using the synthesized PNIPAM samples covering a range of degrees of polymerization (N), the scaling analysis in the relationship of R_H N^谓 exhibits a progressive, re-entrant change of the scaling index (谓) between good solvent (0.57) and poor solvent (1/3) condition, which is a reflection of a re-entrant conformational transition of the polymers. Furthermore, the highly asymmetrical feature of the cononsolvency process of single PNIPAM chains was unveiled, which indicates a much stronger effect or interaction of the ethanol molecules to the PNIPAM chain. Comparisons of the present results with previous reports provided new information to the mechanism model of the PNIPAM cononsolvency.