(437g) Exploring Solid-Fluid Phase Behavior of Adsorbed Water Nanoconfined Between Mica and Graphene Surfaces

The behavior of an adsorbed water phase on the nanoscale is of particular importance to the field of nanofluidics and the lab-on-a-chip concept, where fluid structure and behavior at the nanoscale governs the systems under consideration. Experimental evidence supports the existence of a fluid water layer inside a graphene-mica slit pore with virtually no defects (Xu et al., Science 2010, 329, 1188), while defective surfaces cause liquid-solid transitions within the adlayer (Severin et al., Nano Letters 2012 12, 774-779). The structure of these “ices” is of interest due to the effects of confinement, which may cause exotic crystalline phases to form (Jazdzewska et al., Phys. Chem. Chem. Phys. 2011, 13, 9008-9013)

            Water adsorption in the graphene-mica slit pore was simulated by the grand canonical Monte Carlo method, mirroring experimental conditions. The mica surface was modeled using Steele’s potential, while the graphene surface was modeled as either a smooth wall with Steele’s potential or a flexible atomistic wall. The TIP4P/2005 model was used to model the interaction between water molecules. The final configurations of water were analyzed with specific order parameters tuned to detect the various crystalline ice phases. By varying the temperature of the simulation, freezing transitions can also be deduced.

            Our simulation results support the experimental observations that defects can induce crystallization of adsorbed water. These simulations also provide an understanding of the freezing behavior of water confined within the graphene-mica slit pore system.