|
楼主 |
发表于 2006-6-30 23:17:20
|
显示全部楼层
引用第8楼hooker于2006-06-30 08:14发表的“”:
水-冰在自然常态下的体积变化是由于氢键的作用吧
高分子体积反常变化利用的是什么微观特性?
For water, I am sure you are on the right track. For polymer such as PNIPAm, the debate is always there. As yet, people think the microscopic driving force is the hydrophobic interaction between isopropyl groups on the polymer backbones. If the temperature is lower than the LCST, water molecules attached on amide groups with directed H-bonds, sort of crystalline water structure on the backbone, which macroscopically swell the polymer chain, therefore, water is good solvent at this time. Flory solvation coefficient"Kai"<0.5. However, if the temperature is higher than the LCST, the hydrophobic interaction between isopropyl groups will dominate the configuration of the polymer backbone, which might squeeze water out to the solvent(also water) bulk. The debate is here also, how this occurs? Nobody provide convincing experimental evidence yet. |
|