Neutron Science Laboratory, Institute for Solid State Physics, University of Tokyo, 106-1 Shirakata, Tokai, Ibaraki 319-1106, Japan.
J Phys Chem B. 2009 Oct 1;113(39):12870-6. doi: 10.1021/jp902960b.
Dynamics of water and poly(N-isopropylacrylamide) (PNIPA) in concentrated aqueous solutions, where the majority of water molecules are attached to polymer chains, has been investigated with use of incoherent quasi-elastic neutron scattering (QENS) and dynamic light scattering (DLS) measurements as functions of temperature, T, and hydrostatic pressure, P. It was observed by QENS that the self-diffusion coefficient, D(water), of water in PNIPA/H(2)O solutions increased by P at temperatures below the lower critical solution temperature (LCST) of PNIPA aqueous solutions. However, above the LCST, D(water) decreased by P, as is often reported in non-hydrogen bonding solutions. In isobaric heating runs, therefore, the jump in D(water) at LCST decreased with increasing pressure. On the other hand, the mean-square displacement, <u(2)>, of the local vibrational motion of PNIPA in PNIPA/D(2)O solutions, where the incoherent scattering signal of PNIPA was predominantly observed, was reduced due to the aggregation behavior of PNIPA by pressurizing, which was also confirmed by using DLS. The jump in <u(2)> at the LCST became gradual by pressurizing, which was consistent with the changes of the dynamics of water obtained in PNIPA/H(2)O solutions.
在高浓度的水溶液中，大多数水分子都与聚合物链相连，我们利用非相干的准弹性中子散射（QENS）和动态光散射（DLS）技术，研究了水和聚 N-异丙基丙烯酰胺（PNIPA）的动力学。结果表明，在 PNIPA 水溶液的低临界溶液温度（LCST）以下，QENS 观察到 PNIPA/H2O 溶液中水分子的自扩散系数 D（water）随压力的增加而增加。然而，在 LCST 以上，D（water）随压力的增加而减小，这在非氢键溶液中经常被报道。因此，在等压加热过程中，LCST 处 D（water）的跃变随着压力的增加而减小。另一方面，在 PNIPA/D2O 溶液中，PNIPA 的局部振动运动的均方位移 <u(2)> 减小，因为 PNIPA 的聚集行为导致了散射信号的增强，这也通过 DLS 得到了证实。在 LCST 处的 <u(2)> 的跃变随着压力的增加而逐渐变得平缓，这与在 PNIPA/H2O 溶液中获得的水动力学变化一致。
