Research Projects

This research is motivated by the need to better understand the phase diagram of supercooled water, particularly in light of the recent discovery of medium-density amorphous (MDA) ice [1] (see Methodology and Research plan for references). Water exhibits glass polyamorphism, existing in various amorphous solid states, primarily low-density amorphous (LDA) ice and high-density amorphous (HDA) ice [2]. Recently, Rosu-Finsen et al [1] discovered a new ho- mogeneous amorphous ice, produced through ball-milling of ice, with a density intermediate to LDA and HDA, called MDA. This discovery adds further complexity to water’s phase di- agram, which includes the aforementioned phenomena of glass polyamorphism, and two-state thermodynamics, featuring coexisting low-density liquid (LDL) and high-density liquid (HDL) phases [3]. The discovery of MDA complicates the idea of LDL and HDL which are commonly associated with LDA and HDA, respectively. In simulations, a variety of intermediate amor- phous (IA) ices [4] and shear-driven amorphous (SDA) ices [5] are formed between LDA and HDA. These are produced through isobaric cooling at different pressures and by shearing ices or amorphous water phases (LDA and HDA) at varying rates, respectively. Simulations suggest structurally similar MDA is found as part of a spectrum of IA and SDA. Experiment suggests that MDA may represent liquid water prior to phase separation into LDA and HDA, or a heavily sheared crystalline state disconnected from the liquid phase [5], while computational simulation describe it as a non-equilibrium, shear-driven amorphous phase, distinct from both LDA and HDA . However, the identification of any associated liquid phase, as well as the precise nature of MDA, remains inconclusive in both experimental and simulation studies, making it a com- pelling topic for further research into water’s complex phase behavior. In this study, we aim to explore the modified phase diagram of water, with a particular focus on the supercooled regime under the influence of MDA. Glasses are typically characterized as non-equilibrium liquids associated to an equilibrium liquid at a temperature T . Can a similar framework be applied to MDA? Specifically, can the potential energy landscape (PEL) approach [6] be employed to investigate this? The PEL approach has proven effective for constructing phase diagrams at low temperatures, where conventional simulations become difficult due to the sluggish dynamics of water [10,11]. Shearing of glasses typically results in rejuvenation [8] but the polyamorphism of water allows aging through steady shear of HDA ice at some specific shear rates [5]. It is exciting for further investigation into the PEL as an interplay of shear rate and temperature to reveal intriguing properties of SDA and associate liquid phase if any.