The solvent quality of water for poly(N-isopropylacrylamide) in the collapsed state: Implications from single-molecule studies
The solvent quality of water for poly(N-isopropylacrylamide) in the collapsed state: Implications from single-molecule studies
复制标题
DOI：
10.1007/s10118-016-1773-9
复制
发表时间：
2016-02
影响因子：
4.3
通讯作者：
X. Pang;Bo Cheng;Shuxun Cui
中科院分区：
文献类型：
--
作者：
X. Pang;Bo Cheng;Shuxun Cui
温度（水中）和组成（水/甲醇混合溶剂中）均能诱导聚N-异丙基丙烯酰胺（PNIPAM）的线团-球转变。基于原子力显微镜（AFM）的单分子力谱（SMFS）技术可以在单分子水平上研究高分子链与溶剂之间的相互作用。结果表明，PNIPAM的单链结构对两种外界刺激具有显著的依赖性。一个令人困惑的实验结果是，所有的力-延伸（F-E）曲线展开一个单独的PNIPAM球呈现弹性（单调增加的力）拉伸，而不是高原（恒定的力）拉伸理论预测的功能。本文阐明了单链球内部溶剂分子的存在是造成理论和实验F-E曲线不一致的原因。虽然这两种外部刺激都倾向于降低PNIPAM的溶剂质量，但水和水/甲醇混合溶剂永远不会是PNIPAM的强不良溶剂，即使在最差的条件下。
Both of temperature (in water) and composition (in the water/methanol mixed solvent) can induce the coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPAM). The atomic force microscope (AFM) based single molecule force spectroscopy (SMFS) has been exploited to investigate the interactions between the polymer chain and solvent at the single-molecule level. It is found that the single-chain mechanics of PNIPAM show a remarkable dependence on the two external stimuli. A confusing experimental result is that all the force-extension (F-E) curves of unfolding an individual PNIPAM globule present a feature of elastic (monotonically increasing force) stretching but not plateau (constant force) stretching predicted by theory. In this article, we clarify that the presence of the interior solvent molecules in the single-chain globule is the origin of the discrepancy between the F-E curves obtained from theory and experiment. Although both of the external stimuli do tend to lower the solvent quality for PNIPAM, water and the water/methanol mixed solvent will never be the strongly poor solvent for PNIPAM, even at the worst condition.