Ice growth phenomenology in the presence of non-electrolytes: from small molecules to antifreeze proteins
Ice is a well known material, and is found in a variety of shapes on earth and its atmosphere. Despite all the investigations on ice, the molecular details of its growth from a liquid phase have yet to be resolved. Molecular-level understanding of ice growth helps better controlling and engineering ice formation in cryopreservation, cryosurgery and the food industry. In this thesis, the growth of ice from pure melt and solution is investigated using a molecular dynamics approach. The formation and evolution of water rings have been the focus of this work in the case of ice growth from pure water as well as the influence of non-electrolyte solutes and gas hydrates. In the case of growth from pure water, the key single and coupled ring features participating in the transition of water to ice have been identified. While the presence of non-electrolyte solutes typically suppresses the populations of these rings, it can enhance formation of a special feature on the surface of ice, identified as the coupled 5-8 ring defect, which can play an essential role in promoting stacking faults within the ice crystal. The coupled 5-8 ring defects can initiate structural fluctuations promoting occurrence of 5-member rings in the case of a supersaturated methane solution, elevating the local density of methane molecules and ultimately nucleating an amorphous phase of methane clathrate hydrate. Furthermore, the coupled 5-8 ring defects appear to serve as grain boundaries, and potentially inhibit recrystallization of ice crystals, particularly in the presence of antifreeze proteins (AFPs). The relative structural flexibility of AFPs, their ability to retain the hydration shell upon crystallization of bulk water and the hydrophobic nature of their ice binding site apparently enable them to induce these defects when they interact with the pyramidal faces of hexagonal ice. In addition to the structural descriptions of the ice-water interface, thermodynamic properties such as energy, entropy, and free energy across the ice-water interface have been estimated. Furthermore, a stepwise evolution of order is observed during the growth of ice using the populations of single and coupled rings as order parameters. A crystallization funnel is suggested which captures the structural and thermodynamic evolution of water molecules towards the crystalline state. In addition to the molecular-level insights into the ice growth, this thesis also provides suggestions for future explorations.
Pirzadeh, P. (2012). Ice growth phenomenology in the presence of non-electrolytes: from small molecules to antifreeze proteins (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26412