Temperature- and Tension-Induced Coil-Globule Transition of Poly(N-isopropylacrylamide) Chains in Water and Mixed Solvent of Water/Methanol
Temperature- and Tension-Induced Coil-Globule Transition of Poly(N-isopropylacrylamide) Chains in Water and Mixed Solvent of Water/Methanol
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DOI：
10.1021/ma801982e
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发表时间：
2009-02-24
期刊：
影响因子：
5.5
通讯作者：
Winnik, Francoise A.
中科院分区：
文献类型：
--
作者：
Tanaka, Fumihiko;Koga, Tsuyoshi;Winnik, Francoise A.
协同脱水的概念被用来研究聚(N-异丙基丙烯酰胺)(PNIPAM)在水溶液中加热时链的断裂。我们考察了这一概念在三种情况下的适用性：(I)PNIPAM在水中(在没有附加力的情况下)，(Ii)PNIPAM在水中受到链端的张力，以及(Iii)PNIPAM在水和第二水可混溶溶剂的混合溶剂中。随着水化协同性参数的增加，转变变得更加尖锐。用类似于经典螺旋转变理论的方法计算了水合链在不同温度下的拉伸-伸长曲线，该曲线与折叠段从球体中卷出的张力相对应。卷出的节段在暴露在水中后立即水合。计算表明，在剪切流作用下，PNIPAM水溶液的浊点可能向更高的温度移动。从聚合物-水和聚合物-甲醇之间的竞争氢键的角度，研究了水和甲醇混合溶剂中的卷曲-球状-卷曲相变。
The concept of cooperative dehydration, defined as the simultaneous dissociation of the water Molecules bound in correlated sequences to a polymer chain, has been applied to study the collapse of a poly(N-isopropylacrylamide) (PNIPAM) chain upon heating in aqueous solutions. We examined the applicability of this concept in three situations: (i) PNIPAM in water (in the absence of added force), (ii) PNIPAM in water Subjected to a tension applied to the chain ends, and (iii) PNIPAM in a mixed solvent of water and a second water-miscible solvent. The transition becomes sharper as the cooperativity parameter of hydration increases. The tension-elongation curve of a hydrated chain at various temperatures, calculated following an approach similar to the classical theory of coil - helix transition, presents a flat plateau corresponding to the tension for which collapsed segments reel out of the globules. The reeled-out segments are hydrated immediately upon exposure to water. The calculations suggest a possible shift to higher temperatures of the cloud points of aqueous PNIPAM solutions under shear flow. The reentrant coil-globule-coil transition in mixed solvent of water and methanol is studied from the viewpoint of competitive hydrogen bonds between polymer-water and polymer methanol.