Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Tokyo 152-8551, Japan.
J Phys Chem B. 2011 Dec 8;115(48):14023-9. doi: 10.1021/jp2034032. Epub 2011 Aug 19.
At what temperature between 136 and 165 K the glass transition of water occurs is still controversial, while the crystallization of water prevents the determination. To confine water in nanopores stabilizes its liquid state down to low temperatures. Heat capacities and enthalpy relaxation effects of the water confined within MCM-41 nanopores with diameters in the range 1.5-5.0 nm were measured in this work by using adiabatic calorimetry. No fusion of the confined water was detected up to 2.0 nm, part of the water exhibited fusion in 2.1 nm pores, and the whole internal water which excludes the molecules interacting with the pore-wall atoms crystallized within pores with diameter of 2.3 nm and above. A glass transition of the internal water occurred at a temperature T(g) = 160-165 K for pore diameters in the range 1.5-2.0 nm and at 205-210 K for diameters of 2.0 and 2.1 nm; thus, the T(g) jumped from 165 to 205 K at 2.0 nm. The jump is connected to the development of hydrogen-bond network to a more complete one as the diameter is increased, and is conjectured as caused by the increase in the number, from three to four, of hydrogen bonds formed by each molecule. These imply that the glass transition of bulk water occurs at 210 K, which is much higher than 136 or 165 K debated so far.
在 136 到 165 K 之间，水的玻璃化转变温度仍存在争议，而水的结晶则阻止了这一温度的确定。将水限制在纳米孔中可以稳定其液态至低温。本工作通过使用绝热量热法测量了直径在 1.5-5.0nm 范围内的 MCM-41 纳米孔中受限水的热容和焓弛豫效应。在 2.0nm 以下，未检测到受限水的熔融；部分水在 2.1nm 孔中表现出熔融；而直径为 2.3nm 及以上的孔内，所有排除与孔壁原子相互作用的分子的内部水都结晶。对于直径为 1.5-2.0nm 的孔，内部水的玻璃化转变温度为 T(g)=160-165K；对于直径为 2.0 和 2.1nm 的孔，温度为 205-210K；因此，在 2.0nm 时，T(g)从 165K 跃升至 205K。这种跃迁与氢键网络的发展有关，随着直径的增加，氢键网络变得更加完整，据推测这是由于每个分子形成的氢键数量从 3 个增加到 4 个所致。这意味着，与目前争议的 136K 或 165K 相比，体相水的玻璃化转变温度发生在 210K。
