This is a progress report on elucidating the behaviour of liquids, in particular water, in confined geometry on the nano- to mesoscale, and at interfaces. There are important measurements still to make, conclusions still to be drawn, and above all leaps of understanding still to be made. However, a number of important features in the behaviour of these systems have recently become clearer. Nano-structuring of liquids and their crystals changes their Gibbs free energy, and hence their dynamics. This may most readily be probed by monitoring the alteration of phase changes as a function of temperature, together with changes in other parameters, particularly the confinement diameter. Such studies may be performed by monitoring the change in the pressure (at constant temperature) of the liquid in its own vapour (Kelvin equation), or by monitoring the change in the freezing/melting temperature (at constant pressure) of a crystal in its own liquid (Gibbs–Thomson equation). In the latter case the melting and freezing temperatures of liquids are modified by the changes in the volumetric Gibbs free energy due to nanostructuring; this is related to the surface energy of the curved interface between the crystal and its own liquid. This is thus dependent on the geometry of the interface between the crystal and its liquid. There is still discussion on this point as to the exact geometric constants and functional forms that are applicable for different confining geometries. Experimental evidence is presented for the cases of cylindrical pores (SBA-15), and for pores that on average are spherical (sol–gel). However, reconciling this comparative data with melting/freezing temperatures in each of these systems still pose a number of questions. It is well known that bulk brittle ice has a hexagonal structure, while brittle ice that forms in pores may be cubic in structure [1,2], Figs. 10 and 11. Adjacent surfaces appear to further alter the dynamics and structure of confined liquids and their crystals, leading in the case of a water/ice system to a state of enhanced rotational motion (plastic ice) just below the confined freezing/ melting transitions. This plastic ice layer appears to form at both the ice–silica interface and the ice–vapour surface, and reversibly transforms to brittle ice at lower temperatures. There is good evidence to suggest that the plastic ice at a silica interface transforms to cubic ice, while the plastic ice at vapour surfaces transforms to hexagonal ice. That this plastic ice may correspond to a layer at the crystal surface is suggested by the presence of only amorphous ice in confined systems with small dimensions (<3 nm diameter), whereas systems with larger dimensions (10 nm) contain brittle cubic ice and also some hexagonal ice (if a vapour interface is present); even larger systems (>30 nm) contain predominately hexagonal ice. It is conjectured that this layer of plastic ice at vapour surfaces may be present at the myriad of such interfaces in macroscopic systems, such as snow-packs, glaciers and icebergs, and may be an explanation for the need for plastic terms in the macroscopic dynamical models of these systems [3]. These results also point the way forward for a wide-range of cryoporometric metrology studies of systems that are ‘difficult’ for NMR, such as high iron content clays and rocks, as well as aged concrete. Results are presented for cryoporometric measurements on meteorite samples with a significant metallic content, exhibiting T2 relaxation times down to 2.5 us.

中文翻译：

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研究受限几何形状和表面的纳米结构液体

这是一份关于在纳米到中尺度的受限几何中以及在界面上阐明液体（尤其是水）行为的进展报告。仍有重要的衡量标准有待进行，仍有待得出结论，最重要的是，仍有待实现理解的飞跃。然而，这些系统行为中的许多重要特征最近变得更加清晰。液体及其晶体的纳米结构改变了它们的吉布斯自由能，从而改变了它们的动力学。通过监测作为温度函数的相变变化以及其他参数的变化，特别是限制直径的变化，可以最容易地探测到这一点。可以通过监测液体在其自身蒸气中的压力变化（在恒定温度下）进行此类研究（开尔文方程），或者通过监测晶体在其自身液体中的冷冻/熔化温度（在恒定压力下）的变化（吉布斯-汤姆森方程）。在后一种情况下，由于纳米结构导致的体积吉布斯自由能变化，液体的熔化和凝固温度会发生变化；这与晶体与其自身液体之间弯曲界面的表面能有关。因此，这取决于晶体与其液体之间界面的几何形状。关于适用于不同约束几何的确切几何常数和函数形式，关于这一点仍有讨论。为圆柱孔 (SBA-15) 和平均为球形的孔 (溶胶-凝胶) 提供了实验证据。然而，将这些比较数据与这些系统中的每一个的熔化/冻结温度进行协调仍然提出了许多问题。众所周知，大块脆冰具有六方结构，而在孔隙中形成的脆冰可能是立方结构 [1,2]，图 1 和图 2。10 和 11. 相邻表面似乎进一步改变了受限液体及其晶体的动力学和结构，导致在水/冰系统的情况下，在受限冻结/融化转变的正下方进入增强的旋转运动（塑料冰）状态. 这种塑料冰层似乎在冰-二氧化硅界面和冰-蒸气表面形成，并在较低温度下可逆地转变为脆冰。有充分的证据表明二氧化硅界面处的塑料冰转变为立方冰，而蒸汽表面的塑料冰转变为六边形冰。这种塑性冰可能对应于晶体表面的一层，这表明在小尺寸（<3 nm 直径）的受限系统中仅存在无定形冰，而较大尺寸（10 nm）的系统包含脆性立方冰，并且一些六边形冰（如果存在蒸汽界面）；甚至更大的系统（>30 nm）主要包含六边形冰。据推测，蒸汽表面的这层塑性冰层可能存在于宏观系统中的无数此类界面处，例如积雪、冰川和冰山，这可能解释了宏观动力学中需要塑性术语的原因。这些系统的模型 [3]。这些结果还为对 NMR“困难”的系统（例如高铁含量粘土和岩石以及老化混凝土）进行广泛的低温孔隙计量学研究指明了前进方向。结果显示为对具有显着金属含量的陨石样品进行低温孔隙测量，其 T2 弛豫时间低至 2.5 us。