The origin of water anomalies, such as volume expansion upon cooling, is essentially important for the understanding of different chemical and biological processes which involve water. Researchers from theoretical and experimental communities are testing the hypothesis which can potentially explain all water anomalies, namely the existence of a second liquid-liquid critical point in supercooled water that was first proposed by Poole et al. (P. H. Poole, F. Sciortino, U. Essmann, and H. E. Stanley, Nature 360: 324, 1992).

This paper is a synthesis of knowledge that encloses a wide range of information from computational and experimental communities.

Compared to theoretical studies, experimentalists have made rapid "progress" recently by discovering the idea of confining water in nanoporous materials. In this way, water can be prevented from crystallization, allowing it to stay in the liquid state deep into the supercooled region.

Our work provides an explanation of recent experimental discoveries, arousing great interest among researchers who are concerned about the low temperature properties of water.

  Does it describe a new discovery, methodology, or synthesis of knowledge?

This paper is a synthesis of knowledge that encloses a wide range of information from computational and experimental communities.

Our work shows that the hypothesized critical point influences the thermodynamic and dynamic properties both below and above the phase separation region. Moreover, we show that when compared to the two-phase region in which metastability normally occurs, it is easier to detect the critical point effect in the one phase region by tracing the response function maxima (the Widom line).

  Could you summarize the significance of your paper in layman’s terms?

According to our study, if there is a critical point, the Widom line exists. When the critical point is inaccessible due to technical difficulties, such as crystallization, one can trace the Widom line until it terminates at the critical point.

This is essentially important for the experimental studies of supercooled water, which crystallizes at low temperatures. Our work maps a way for an experiment to approach the elusive liquid-liquid critical point.

  How did you become involved in this research, and were any problems encountered along the way?

Our group has been interested in an understanding of the origin of water anomalies for a long time. This specific work was inspired by a recent experimental discovery (dynamic crossover) by Chen et al. (L. Liu, S.-H. Chen, A. Faraone, C.-W. Yen, and C.-Y. Mou, Phys. Rev. Lett. 95: 117802, 2005). Specifically, we wanted to understand the possible link of the dynamic crossover of confined water with a possible liquid-liquid critical point.