Taschin A, Bartolini P, Marcelli A, Righini R, Torre R
European Laboratory for Non-Linear Spectroscopy (LENS), Università di Firenze, Via N. Carrara 1, I-50019 Sesto Fiorentino, Firenze, Italy.
J Phys Condens Matter. 2015 May 20;27(19):194107. doi: 10.1088/0953-8984/27/19/194107. Epub 2015 Apr 29.
Using heterodyne-detected optical Kerr effect (HD-OKE) measurements, we investigate the vibrational dynamics and the structural relaxation of water nanoconfined in Vycor porous silica samples (pore size ≃ 4 nm) at different levels of hydration and temperatures. At low levels of hydration corresponding to two complete superficial water layers, no freezing occurs and the water remains mobile at all the investigated temperatures with dynamic features similar, but not equal to, the bulk water. The fully hydrated sample shows the formation of ice at about 248 K. This process does not involve all the contained water; a part of it remains in a supercooled phase. The structural relaxation times measured from the decay of the time-dependent HD-OKE signal shows the temperature dependence largely affected by the hydration level; the low frequency (ν < 500 cm(-1)) vibrational spectra obtained by the Fourier transforms of the HD-OKE signal appear less affected by confinement.
通过外差检测光学克尔效应（HD-OKE）测量，我们研究了在不同水合水平和温度下，Vycor多孔二氧化硅样品（孔径≃4nm）中纳米限域水的振动动力学和结构弛豫。在对应于两个完整表面水层的低水合水平下，不会发生冻结，并且水在所有研究温度下均保持流动，其动态特征与 bulk water 相似但不相同。完全水合的样品在约248K时显示出冰的形成。此过程并不涉及所有所含的水；其中一部分仍处于过冷相。从随时间变化的HD-OKE信号的衰减测量得到的结构弛豫时间表明，温度依赖性在很大程度上受水合水平影响；通过HD-OKE信号的傅里叶变换获得的低频（ν<500cm(-1)）振动光谱似乎受限域影响较小。
