Probing the Structure of Water on Surfaces: From Water Absorption to Ice Nucleation

Water, essential for all life forms, is the most abundant, simple, yet mysterious molecule in the world. This molecule, consisting of only three atoms, behaves in unexpectedly different ways with the change of environment. In the past, studies of water under different conditions (temperature, pressure, on the surfaces, with confinement) have been conducted using experimental and computational methods. However, the influence of a given environment on water properties is yet to be fully understood. This dissertation studies water at complex interfaces (surfaces with various chemistry and physics properties) in both the liquid and crystalline states. Various heterogeneous systems used to study the water adsorption, surface ion adsorption in the aqueous phase, and ice nucleating ability of different substrates is covered in this work. We apply molecular dynamics (MD) and density functional theory (DFT) to study the interplay of surface properties on water behavior. In addition, we extend the knowledge of the influence of liquid water properties on nucleating abilities without simulating nucleation.We investigated the effects of the ions’ charge, type, and displacements on the mica surface on interfacial water behavior at both room temperature and freezing conditions. We found that the mica surfaces substituted with multivalent charged cations are better nucleating agents due to their ability to promote the formation of large, stable water clusters in the regions where no ions are adsorbed. Moreover, to uncover the role of bare mica (areas with no ions adsorbed), we have applied a novel seeding method developed by our group to study the ice nucleation on mica surfaces with multiple ion displacements. The ions orient the surrounding water in a form different from the ice-like structure, restraining their ability to re-orient, thus reducing the nucleating propensity. Surfaces that promote nucleation must be able to localize water molecules to create hydrogen-bonded water clusters while also orienting them in a manner that allows flexibility to reorient and form an ice-like structure, thus minimizing the entropy penalty.