Physik-Department, Lehrstuhl für Funktionelle Materialien/Physik Weicher Materie, Technische Universität München, James-Franck-Str.1, 85748 Garching, Germany.
Langmuir. 2012 Jun 12;28(23):8791-8. doi: 10.1021/la3015332. Epub 2012 May 31.
The phase separation mechanism in semidilute aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions is investigated with small-angle neutron scattering (SANS). The nature of the phase transition is probed in static SANS measurements and with time-dependent SANS measurements after a temperature jump. The observed critical exponents of the phase transition describing the temperature dependence of the Ornstein-Zernike amplitude and correlation length are smaller than values from mean-field theory. Time-dependent SANS measurements show that the specific surface decreases with increasing time after a temperature jump above the phase transition. Thus, the formation of additional hydrogen bonds in the collapsed state is a kinetic effect: A certain fraction of water remains as bound water in the system. Moreover, H-D exchange reactions observed in PNIPAM have to be taken into account.
利用小角中子散射（SANS）研究了半浓水相聚 N-异丙基丙烯酰胺（PNIPAM）溶液中的相分离机制。通过静态 SANS 测量和温度跃变后的时变 SANS 测量来探测相转变的性质。观察到的相转变的描述奥恩斯坦-泽尔尼克幅度和相关长度随温度变化的临界指数小于平均场理论的值。时变 SANS 测量表明，在温度跃变到相转变以上后，特定表面积随时间的增加而减小。因此，在塌陷状态下形成额外氢键是一种动力学效应：系统中仍有一定比例的水作为结合水。此外，还必须考虑在 PNIPAM 中观察到的 H-D 交换反应。
