Liquid-Liquid Phase Transitions and Water-Like Anomalies in Liquids

Speaker: Erik Lascaris

When: July 9, 2014 (Wed), 11:00AM to 12:00PM (add to my calendar)
Location: SCI 352

This event is part of the PhD Final Oral Exams.

Examining Committee: H.E. Stanley, William Skocpol, Shyam Erramilli, Karl Ludwig, Robert Carey

Lascaris

ABSTRACT: Of the three classical states of matter, the liquid state seems to be the most challenging phase to characterize. It exhibits neither the long-range order of the crystalline state nor the complete disorder of the gaseous state. Located between gas and solid in the phase diagram, it is no surprise that the physics of liquids is a rich field full of interesting phenomena.

Among liquids, water is particularly fascinating. It is the most common liquid on the surface of the Earth, it makes up over 50% of the human body, and many important chemical and biological processes occur within its aquatic environment. H2O is one of the simplest molecules, yet it condenses into an unusually complex liquid. Compared with other liquids, water has many anomalies, e.g., its liquid form has a higher density than its solid form, when the liquid is cooled below 4 C the density decreases rather than increases, and when the pressure is increased its self-diffusion increases rather than decreases.

Cooling liquid water to below its melting temperature under certain experimental conditions produces metastable supercooled liquid water. In this state the anomalies become even more distinct. For example, there is a steep increase in both the heat capacity and the compressibility when supercooled liquid water is cooled to approximately --40 C. Although many water anomalies can be explained with reference to its hydrogen bonds, this steep increase suggests an interesting possibility: the existence of two distinct liquid phases, separated by a first-order-like liquid-liquid phase transition (LLPT) that ends in a critical point.

Water-like anomalies and LLPTs are by no means limited to water, however. Other tetrahedral liquids, such as silica, share several of these anomalies and may also have a LLPT. We study the general mechanism that lies behind these anomalies, and investigate a possible link with LLPTs. In addition we consider various methods to prove or disprove the existence of a LLPT, and discuss possible methods of predicting the existence of a LLPT based on data at temperatures above the critical temperature.