Both of temperature（in water） and composition（in the water/methanol mixed solvent） can induce the coil-toglobule transition of poly（N-isopropylacrylamide）（PNIPAM）. The atomic force microscope（AFM） based sing...Both of temperature（in water） and composition（in the water/methanol mixed solvent） can induce the coil-toglobule 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.展开更多
基金supported by the National Natural Science Foundation of China(Nos.21074102 and 21222401)
文摘Both of temperature（in water） and composition（in the water/methanol mixed solvent） can induce the coil-toglobule 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.
