Collapse of a poly（N-isopropylacrylamide） （PNIPAM） chain upon heating and phase diagrams of aqueous PNIPAM solutions with very fiat LCST phase separation line are theoretically studied on the basis of cooperative ...Collapse of a poly（N-isopropylacrylamide） （PNIPAM） chain upon heating and phase diagrams of aqueous PNIPAM solutions with very fiat LCST phase separation line are theoretically studied on the basis of cooperative dehydration （simultaneous dissociation of bound water molecules in a group of correlated sequence）, and compared with the experimental observation of temperature-induced coil-globule transition by light scattering methods. The transition becomes sharper with the cooperativity parameter σ of hydration. Reentrant coil-globule-coil transition in mixed solvent of water and methanol is also studied from the viewpoint of competitive hydrogen bonds between polymer-water and polymer-methanol. The downward shift of the cloud-point curves （LCST cononsolvency） with the mole fraction of methanol due to the competition is calculated and compared with the experimental data. Aqueous solutions of hydophobically-modified PNIPAM carrying short alkyl chains at both chain ends （telechelic PNIPAM） are theoretically and experimentally studied. The LCST of these solutions is found to shift downward along the sol-gel transition curve as a result of end-chain association （association-induced phase separation）, and separate from the coil-globule transition line. Associated structures in the solution, such as flower micelles, mesoglobules and higher fractal assembly, are studied by USANS with theoretical modeling of the scattering function.展开更多
基金supported by a Grant-in-Aid for Scientific Research on Priority Areas"Soft Matter Physics"from the Ministry of Education,Culture,Sports,Science and Technology of Japan,and partly supported by a Grant-in-Aid for Scientific Research(B) from the Japan Society for the Promotion of Science under grant number 19350057
文摘Collapse of a poly（N-isopropylacrylamide） （PNIPAM） chain upon heating and phase diagrams of aqueous PNIPAM solutions with very fiat LCST phase separation line are theoretically studied on the basis of cooperative dehydration （simultaneous dissociation of bound water molecules in a group of correlated sequence）, and compared with the experimental observation of temperature-induced coil-globule transition by light scattering methods. The transition becomes sharper with the cooperativity parameter σ of hydration. Reentrant coil-globule-coil transition in mixed solvent of water and methanol is also studied from the viewpoint of competitive hydrogen bonds between polymer-water and polymer-methanol. The downward shift of the cloud-point curves （LCST cononsolvency） with the mole fraction of methanol due to the competition is calculated and compared with the experimental data. Aqueous solutions of hydophobically-modified PNIPAM carrying short alkyl chains at both chain ends （telechelic PNIPAM） are theoretically and experimentally studied. The LCST of these solutions is found to shift downward along the sol-gel transition curve as a result of end-chain association （association-induced phase separation）, and separate from the coil-globule transition line. Associated structures in the solution, such as flower micelles, mesoglobules and higher fractal assembly, are studied by USANS with theoretical modeling of the scattering function.
