Grant: Discovery Grants Program - Individual

This proposal aims to make progress on a set of associated fronts: the curious thermodynamics of deeply supercooled liquid water and how to measure it; the way properties of water nanodroplets change with size and temperature and how this affects the structure of biomolecules contained within them; how to better control or prevent the formation of ice so as to prevent the damage it cause to cells; the nature of crystallization, especially when different types of crystals can form out of the same parent material, as in the shells of marine creatures; and the ways we can use colloidal suspensions to learn about fundamental processes going on in molecular liquids while generating new types of materials. The liquid state is the centrepiece in all these fronts, and the computer simulation techniques we use are applicable to both learning about liquids in their simplest form, as well as the more complex systems in the proposal. There is mounting experimental evidence that liquid water below -50 °C can exist in two forms: a high-density liquid (HDL) phase at larger pressures and low-density liquid (LDL) at ambient pressure, with a phase transition separating the two. Definitively showing this to be true is frustratingly difficult on account of rapid crystallization of water at such low temperatures. Nanodroplets resist freezing because they are so small, and thus are enticing systems to study deeply supercooled water. Furthermore, for a popular molecular water model, we showed in earlier work that the interior pressure of nanodroplets reaches over 100 MPa while the droplet cores are bulk-like. The current proposal will investigate how the HDL-LDL transition manifests itself in nanodroplets for a variety of models, including more recent ones based on first-principles quantum calculations. Our results will guide future experiments and help interpret experimental results in a push to clearly show, or refute, the HDL-LDL transition in water. We will also determine the effect of the HDL-LDL transition on, e.g., the structure of proteins inside nanodroplets, and thus provide a way of manipulating protein structure by changing the size and temperature of the nanodroplets. We will continue with efforts to study crystallization by analyzing the effect of various candidate cryoprotectants on ice formation, applying our recently developed framework for studying so-called "two-step" nucleation to the problem of how marine animals control the formation of different phases of calcium carbonate from solution, and testing frameworks that may provide a unifying understanding of the opposing processes of crystal nucleation and glass formation. In our work on colloids, we will use simulations to understand the connection between structure and dynamics in a new class of colloidal gels recently obtained experimentally by applying external electric fields to colloids systems that otherwise can be understood as attractive hard spheres.