Phys/ANE/ChemPhys Joint Seminar

Date
Wed, Feb 20, 2019 11:00 am - 12:00 pm
Location
Chemistry 0112 (Marker Seminar Room)

Description

Speaker: Professor Sapna Sarupria, Clemson University

Title: Freezing Water and Aqueous Solutions: Elucidating the Molecular Ballet Using Computer simulations

Abstract: Nucleation – that is the onset of a new phase from a metastable phase – is a difficult phenomenon to study both experimentally and computationally. Nucleation relevant spatial and temporal resolution is difficult to access in experiments. In contrast, while computer simulations are perfectly suited to probe these length and
timescales, sampling statistically relevant number of nucleation events is computationally expensive. In our research, we use advanced sampling techniques in conjunction with molecular dynamics simulations to sample hundreds and thousands of nucleation events. We apply these methods to study heterogeneous ice nucleation and gas hydrate nucleation.

Gas hydrates are crystalline (ice-like) solids formed by water forming cages around guest molecules such as methane, carbon dioxide and tetrahydrofuran. These form at low temperatures and high pressure conditions and are a flow assurance problem in the oil and gas industry. In addition, hydrates can be potential energy source, and be used for gas separation and water desalination. The fundamental question that remains unanswered is -- how does the solution of guest and water transform into this crystalline solid. Our simulations provide insights into the mechanisms of hydrate nucleation and highlight its dependence on the water solubility of the guest molecules. These findings will facilitate design of promoters and inhibitors of gas hydrates.

Heterogeneous ice nucleation relates to freezing of water driven by the presence of an impurity such as amineral surface. Interestingly, it is not yet understood what about a surface promotes or inhibits the formation of ice. We use simulations of salt (silver iodide) and mineral (kaolinite) surfaces to provide insights into the properties of a surface that facilitate ice formation. These findings can help design surfaces that either inhibit ice nucleation (for example in cases such as wind mills, power lines, and transportation) or that promote ice nucleation (for example in cases such as food preservation and cryopreservation).

Collectively, my talk provides an overview of the intricate behavior of water molecules in transforming from liquid to the solid phase, and the simulation methods developed to reveal these behaviors.