Oguni Masaharu, Maruyama Satoshi, Wakabayashi Kenji, Nagoe Atsushi
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8551, Japan.
Chem Asian J. 2007 Apr 2;2(4):514-20. doi: 10.1002/asia.200600362.
The dynamic properties of water confined within nanospaces are of interest given that such water plays important roles in geological and biological systems. The enthalpy-relaxation properties of ordinary and heavy water confined within silica-gel voids of 1.1, 6, 12, and 52 nm in average diameter were examined by adiabatic calorimetry. Most of the water was found to crystallize within the pores above about 2 nm in diameter but to remain in the liquid state down to 80 K within the pores less than about 1.6 nm in diameter. Only one glass transition was observed, at T(g) = 119, 124, and 132 K for ordinary water and T(g) = 125, 130, and 139 K for heavy water, in the 6-, 12-, and 52-nm diameter pores, respectively. On the other hand, two glass transitions were observed at T(g) = 115 and 160 K for ordinary water and T(g) = 118 and 165 K for heavy water in the 1.1-nm pores. Interfacial water molecules on the pore wall, which remain in the noncrystalline state in each case, were interpreted to be responsible for the glass transitions in the region 115-139 K, and internal water molecules, surrounded only by water molecules in the liquid state, are responsible for those at 160 or 165 K in the case of the 1.1-nm pores. It is suggested that the glass transition of bulk supercooled water takes place potentially at 160 K or above due to the development of an energetically more stable hydrogen-bonding network of water molecules at low temperatures.
鉴于受限在纳米空间内的水在地质和生物系统中发挥着重要作用，其动态特性备受关注。通过绝热量热法研究了平均直径为1.1、6、12和52 nm的硅胶孔隙中普通水和重水的焓松弛特性。发现大部分水在直径约2 nm以上的孔隙中结晶，但在直径小于约1.6 nm的孔隙中，即使温度降至80 K仍保持液态。在直径为6、12和52 nm的孔隙中，分别仅观察到一个玻璃化转变，普通水的玻璃化转变温度为T(g) = 119、124和132 K，重水的玻璃化转变温度为T(g) = 125、130和139 K。另一方面，在1.1 nm的孔隙中，普通水在T(g) = 115和160 K以及重水在T(g) = 118和165 K时观察到两个玻璃化转变。在每种情况下保持非晶态的孔隙壁上的界面水分子被认为是115 - 139 K区域玻璃化转变的原因，而对于1.1 nm孔隙的情况，仅被液态水分子包围的内部水分子是160或165 K时玻璃化转变的原因。有人提出，由于低温下能量上更稳定的水分子氢键网络的发展，大量过冷水的玻璃化转变可能在160 K或更高温度下发生。
