LASER-LIGHT SCATTERING STUDY OF THE PHASE-TRANSITION OF POLY(N-ISOPROPYLACRYLAMIDE) IN WATER .1. SINGLE-CHAIN
LASER-LIGHT SCATTERING STUDY OF THE PHASE-TRANSITION OF POLY(N-ISOPROPYLACRYLAMIDE) IN WATER .1. SINGLE-CHAIN
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DOI：
10.1021/ma00128a056
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发表时间：
1995-11-20
期刊：
影响因子：
5.5
通讯作者：
ZHOU, SQ
中科院分区：
文献类型：
--
作者：
WU, C;ZHOU, SQ
用静态和动态激光散射研究了窄分布（M（z）/M（w）< 1.05）高分子量（M（w）> 10（7）g/mol）聚（N-异丙基丙烯酰胺）单链在极稀溶液（近似5 μ g/mL）中的线团-球转变。首次观察到了热稳定的塌陷球（R（g）/R（h）= 0.97）。然而，当R（g）/R（h）< 0.97时，单链球是“亚稳的”;即，溶液中的小球仅在有限的时间内是稳定的。在热力学稳定区观察到两阶段链塌缩动力学。在链塌缩和溶解过程中观察到的时间尺度（类似于10（2）s）太短，无法支持先前提出的小球内的高链结密度。R（g）/R（h）可以低至类似于0.62，低于对于均匀密度球体预测的0.774。这一悖论表明，链密度是在球的中心比表面附近的高。高度塌陷的小球在其流体动力学体积中仍含有约80%的水。
The coil-to-globule transition of a single chain of narrowly distributed (M(z)/M(w) < 1.05) high molecular weight (M(w) > 10(7) g/mol) poly(N-isopropylacrylamide) in extremely dilute solutions (similar to 5 mu g/mL) was studied by both static and dynamic laser light scattering. The thermodynamically stable collapsed globule (R(g)/R(h) = 0.97) was observed for the first time. However, when R(g)/R(h) < 0.97, the single-chain globules were ''metastable''; i.e., the globules in the solution were stable only for a finite time. Two-stage chain collapsing kinetics in the thermodynamically stable region was observed. The time scales (similar to 10(2) s) observed in both the chain collapsing and dissolving processes are too short to support the previously suggested high chain-knotting density inside the globule. The R(g)/R(h) can be as low as similar to 0.62, lower than 0.774 predicted for a uniform density sphere. This paradox suggests that the chain density is higher at the center of the globule than that near the surface. The highly collapsed globule still contains similar to 80% water in its hydrodynamic volume.