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Kinetics of Coil-to-Globule Transition of Dansyl-Labeled Poly(N-isopropyl-acrylamide) Chains in Aqueous Solution
Chun-liang Li,Xiao-dong Ye*,Yan-wei Ding,Shi-lin Liu
Author NameAffiliationE-mail
Chun-liang Li Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China  
Xiao-dong Ye* Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China xdye@ustc.edu.cn 
Yan-wei Ding Hefei National Laboratory for Physical Sciences at the Microscale, Structure Research Laboratory, University of Science and Technology of China, Hefei 230026, China  
Shi-lin Liu Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China  
Abstract:
The coil-to-globule transition of thermally sensitive linear poly(N-isopropylacrylamide) (PNIPAM) labeled with dansyl group is induced by 1.54 μm laser pulses (width≈10 ns). The dansyl group is used to follow the transition kinetics because its fluorescence intensity is very sensitive to its micro-environment. As the molar ratio of NIPAM monomer to dansyl group increases from 110 to 300, the effect of covalently attached dansyl fluorophores on the transition decreases. In agreement with our previous study in which we used 8-anilino-1-naphthalensulfonic acid ammonium salt free in water as a fluorescent probe, the current study reveals that the transition has two distinct stages with two characteristic times, namely, τfast≈0.1 ms, which can be attributed to the nucleation and formation of some "pearls" (lo-cally contracting segments) on the chain, and τslow≈0.5 ms, which is related to the merging and coarsening of the "pearls". τfast is independent of the PNIPAM chain length over a wide range (Mw=2.8×106-4.2×107 g/mol). On the other hand, τslow only slightly increases with the chain length.
Key words:  Fluorescence labeling, Laser light scattering, Phase transition, Stimuli-sensitive polymer
FundProject:
荧光标记的聚(N-异丙基丙烯酰胺)链在水溶液中的折叠动力学
李春亮,叶晓东*,丁延伟,刘世林
摘要:
使用1.54 μm的激光脉冲(脉宽约10 ns)诱导丹磺酰基标记的热敏性线性聚N-异丙基丙烯酰胺(PNIPAM)发生线团到小球的转变.当聚合物链中NIPAM单体与丹磺酰基基团的摩尔比由110增至300时,共价键合到聚合物主链上的丹磺酰基发色团对PNIPAM相转变行为的影响会随之减小.PNIPAM链塌缩经历成核过程(伴随着初始珍珠的形成,快弛豫时间τfast=0.1 ms)和珍珠的增长粗化阶段(慢弛豫时间τslow=0.5 ms),这与之前使用水溶性的1-苯胺-8-萘磺酸铵盐作为荧光探针研究PNIPAM在水溶液中的折叠动力学得到的结果类似.τfast在很宽的分子量范围内都与分子量无关,而τslow则随链长增加而略有增大.
关键词:  荧光标记,激光光散射,相转变,刺激响应性聚合物
DOI:10.1088/1674-0068/25/04/389-397
分类号: