Kinetics of Laser-Heating-Induced Phase Transition of Poly(N-isopropylacrylamide) Chains in Dilute and Semidilute Solutions

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• 作者：Yijie Lu ; Xiaodong Ye ; Junfang Li ; Chunliang Li ; Shilin Liu
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：October 27, 2011
• 年：2011
• 卷：115
• 期：42
• 页码：12001-12006
• 全文大小：856K
• 年卷期：v.115,no.42(October 27, 2011)
• ISSN：1520-5207

文摘

The kinetics of the phase transition of poly(N-isopropylacrylamide) (PNIPAM) chains from the dilute regime to the semidilute regime was studied by using a homemade fluorescence spectrometer equipped with an ultrafast pulsed infrared laser (width 10 ns and 位 = 1.54 渭m). We used 8-anilino-1-naphthalensulfonic acid ammonium salt (ANS) free in water as a fluorescent probe to monitor the conformation changes of the PNIPAM chains. Our results have revealed that in the dilute regime there exists two characteristic transition times that are less than 1 ms, namely, 蟿_pearls (0.02 ms), which can be attributed to the nucleation and initial growth of some 鈥減earls鈥?(locally contracting segments) on the chain, and 蟿_coarsening (0.2 ms), which is related to the merging and coarsening of the pearls. At semidilute regime, an extra (third) process (蟿 1.5 ms) appeared, and the contribution from the third process increased with PNIPAM concentration, which can presumably be related to the process of disentanglement of the polymer. A new method to detect the inhomogeneities of the polymer chain segments has been proposed.