Kinetics of Coil-to-Globule Transition of Dansyl-Labeled Poly(N-isopropyl-acrylamide) Chains in Aqueous Solution |
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| Authors: | Chun-liang Li Xiao-dong Ye Yan-wei Ding Shi-lin Liu |
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| Affiliation: | 1.Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China2.Hefei National Laboratory for Physical Sciences at the Microscale, Structure Research Laboratory, University of Science and Technology of China, Hefei 230026, China |
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| 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. |
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| Keywords: | Fluorescence labeling Laser light scattering Phase transition Stimuli-sensitive polymer |
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