Mallamace Francesco, Corsaro Carmelo, Mallamace Domenico, Vasic Cirino, Stanley H Eugene
Faraday Discuss. 2013;167:95-108. doi: 10.1039/c3fd00073g.
The density maximum of water dominates the thermodynamics of the system under ambient conditions, is strongly P-dependent, and disappears at a crossover pressure P(cross) approximately 1.8 kbar. We study this variable across a wide area of the T-P phase diagram. We consider old and new data of both the isothermal compressibility K(T)(T, P), the pressure constant specific heat C(P)(T) and the coefficient of thermal expansion alpha(P) (T, P). We observe that K(T)(T) shows a minimum at T* approximately 315 +/- 5 K for all of the studied pressures, whereas, at the same temperature, C(P)(T) has the minimal variation as a function of P in the interval 1 bar-4 kbar. We find the behavior of alpha(P) also to be surprising: all the alpha(P)(T) curves measured at different P cross at T*. The experimental data show a "singular and universal expansivity point" at T* approximately 315 K and alpha(P)(T*) = 0.44 10(-3) K(-1). Unlike other water singularities, we find this temperature to be thermodynamically consistent in the relationship connecting the three response functions. By considering also the P-T behavior of the self-diffusion coefficient D(S) and of the NMR proton chemical shift delta we have the information that at T* the water local order points out, with decreasing T, the crossover from a normal fluid to the anomalous and complex liquid characterized by the many anomalies.
在环境条件下，水的密度最大值主导着系统的热力学性质，它强烈依赖于压力，并在大约1.8千巴的交叉压力P(cross)下消失。我们在T-P相图的广泛区域研究了这个变量。我们考虑了等温压缩率K(T)(T, P)、定压比热C(P)(T)和热膨胀系数α(P)(T, P)的新旧数据。我们观察到，对于所有研究的压力，K(T)(T)在T约为315±5 K时出现最小值，而在相同温度下，C(P)(T)在1巴至4千巴的区间内随压力的变化最小。我们发现α(P)的行为也令人惊讶：在不同压力下测量的所有α(P)(T)曲线在T处相交。实验数据显示在T约为315 K且α(P)(T) = 0.44×10⁻³ K⁻¹时存在一个“奇异且通用的膨胀点”。与其他水的奇异点不同，我们发现这个温度在连接三个响应函数的关系中在热力学上是一致的。通过考虑自扩散系数D(S)和NMR质子化学位移δ的P-T行为，我们得到信息，即在T*时，随着温度降低，水的局部有序性表明从正常流体向以许多异常为特征的反常且复杂液体的转变。
