Chonde M, Brindza M, Sadtchenko Vlad
Department of Chemistry, The George Washington University, Washington, DC 20052, USA.
J Chem Phys. 2006 Sep 7;125(9):094501. doi: 10.1063/1.2338524.
Using an ultrafast scanning microcalorimetry apparatus capable of heating rates in excess of 10(5) Ks, we have conducted the first direct measurements of thermodynamic properties of pure and doped amorphous solid water (also referred to as low density amorphous ice) in the temperature range from 120 to 230 K. Ultrafast microcalorimetry experiments show that the heat capacity of pure amorphous solid water (ASW) remains indistinguishable from that of crystalline ice during rapid heating up to a temperature of 205+/-5 K where the ASW undergoes rapid crystallization. Based on these observations, we conclude that the enthalpy relaxation time in pure ASW must be greater than 10(-5) s at 205 K. We argue that this result contradicts the assignment of glass transition temperature to 135 K and that ASW may undergo fragile to strong transition at temperatures greater than 205 K. Unlike pure ASW, we observe an approximately twofold rise in heat capacity of CH3COOH doped ASW at 177+/-5 K. We discuss results of past studies taking into account possible influence of impurities and confinement on physical properties of ASW.
我们使用了一种能够实现超过10⁵ K/s加热速率的超快扫描量热仪，首次对120至230 K温度范围内纯的和掺杂的非晶态固体水（也称为低密度非晶冰）的热力学性质进行了直接测量。超快量热实验表明，在快速加热至205±5 K的温度之前，纯非晶态固体水（ASW）的热容与结晶冰的热容没有区别，此时ASW会迅速结晶。基于这些观察结果，我们得出结论，在205 K时，纯ASW中的焓弛豫时间必须大于10⁻⁵ s。我们认为这一结果与将玻璃化转变温度设定为135 K相矛盾，并且ASW在高于205 K的温度下可能会经历从脆性到强性的转变。与纯ASW不同，我们观察到在177±5 K时，CH₃COOH掺杂的ASW的热容大约增加了两倍。我们在考虑杂质和限制对ASW物理性质可能产生影响的情况下，讨论了以往研究的结果。
