Kinetics of laser-heating-induced phase transition of poly(N-isopropylacrylamide) chains in dilute and semidilute solutions.
Kinetics of laser-heating-induced phase transition of poly(N-isopropylacrylamide) chains in dilute and semidilute solutions.
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DOI：
10.1021/jp204853p
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发表时间：
2011-10
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影响因子：
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通讯作者：
Yijie Lu;Xiaodong Ye;Junfang Li;Chunliang Li;Shilin Liu
中科院分区：
文献类型：
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作者：
Yijie Lu;Xiaodong Ye;Junfang Li;Chunliang Li;Shilin Liu
用自制的超快脉冲红外激光(宽度∼10 ns，λ=1.54μm)荧光光谱仪研究了聚N-异丙基丙烯酰胺(PNIPAM)链从稀相到半稀相转变的动力学。我们用8-苯胺基-1-萘磺酸铵盐(ANS)作为荧光探针来监测PNIPAM链的构象变化。我们的结果表明，在稀释区存在两个小于1ms的特征转变时间，即τ(珍珠)(∼0.02ms)和τ(粗化)(∼0.2ms)，前者可归因于链上某些“珍珠”(局部收缩段)的成核和初始生长，后者与珍珠的合并和粗化有关。在半稀释区，出现了一个额外的(第三)过程(τ∼1.5ms)，并且第三个过程的贡献随着PNIPAM浓度的增加而增大，这可能与聚合物的解缠过程有关。提出了一种检测聚合物链段不均匀性的新方法。
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 λ = 1.54 μm). 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, τ(pearls) (∼0.02 ms), which can be attributed to the nucleation and initial growth of some "pearls" (locally contracting segments) on the chain, and τ(coarsening) (∼0.2 ms), which is related to the merging and coarsening of the pearls. At semidilute regime, an extra (third) process (τ ∼ 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.