No Confinement Needed: Observation of a Metastable Hydrophobic Wetting Two-Layer Ice on Graphene

Abstract

The structure of water at interfaces is crucial for processes ranging from photocatalysis to protein folding. Here, we investigate the structure and lattice dynamics of two-layer crystalline ice films grown on a hydrophobic substrate, graphene on Pt(111), with low energy electron diffraction, reflection-absorption infrared spectroscopy, rare-gas adsorption/desorption, and ab initio molecular dynamics. Unlike hexagonal ice, which consists of stacks of puckered hexagonal "bilayers", this new ice polymorph consists of two flat hexagonal sheets of water molecules in which the hexagons in each sheet are stacked directly on top of each other. Such two-layer ices have been predicted for water confined between hydrophobic walls, but not previously observed experimentally. Our results show that the two-layer ice forms even at zero pressure at a single hydrophobic interface by maximizing the number of hydrogen bonds at the expense of adopting a nontetrahedral geometry with weakened hydrogen bonds.

Water clustering on nanostructured iron oxide films

“…This result shows that the enhanced hydrophilicity conferred to the surface by the OH groups is lost after formation of the first H 2 O monolayer. This is similar to hydrophobic water layers studied previously on hydrophobic Pt(111) 49 and graphite 50 surfaces as well as on a hydrophilic kaolinite surface 51 . In all these cases, the preferential downward orientation of O-H bonds in the outermost water layers left surfaces devoid of 'dangling H-bonds' which could bind strongly to the next layer of water.…”

Evidence of Stranski–Krastanov growth at the initial stage of atmospheric water condensation

“…In addition, another work 20 , which was performed without graphene coating, also present the similar hexagon shape on mica via scanning polarization force microscopy. At the same time, other experimental and theoretical works have also clearly pointed out a close match between the lattice constant of the water adlayer and the underlying mica substrate 11,[23][24][25][26] . To further reveal the relative orientation of the water adlayer, the atomic structures are recorded by high-resolution AFM.…”

“…Besides, the hydrophobic graphene surface will also guide the water diffusion along the zigzag direction of the C-C bond 26 . Furthermore, previous studies have agreed that no dangling hydrogen bonds are found in the first ice-I h adlayer on mica or the graphene surface 11,24,25 . On the basis of the above analysis, the second and even the third water adlayers should be epitaxially formed at almost zero pressure between mica and the first ice-I h adlayer interface.…”

“…It means that unusual adsorption of the first water adlayer on the hydrophobic graphene occurred, which was known to only exist at cryogenic temperature (between 100 and 140 K; ref. 24). Generally, the binding energy of the water to the hydrophilic substrate is stronger compared with that to the hydrophobic substrate.…”

“…Generally, the binding energy of the water to the hydrophilic substrate is stronger compared with that to the hydrophobic substrate. However, the lack of bonding to the hydrophobic substrate will induce stratification in the water near the interface, which provides the possibility to grow quasi-2D crystalline on the hydrophobic substrate, such as graphene 23,24,27,29 . Even though the detailed mechanism is still unclear, the vicinity of the first water adlayer into graphene instead of the mica surface is probably because of the surface defects on the graphene surface after annealing 11 .…”