Did You Say Hydrophobic Water?

Hydrophobic water sounds like an impossibility. Nevertheless, scientists at Pacific Northwest National Lab have produced and studied monolayers of water molecules (resting on a platinum substrate) which prove to be poor templates for subsequent ice growth. Picture the following sequence: at temperatures below 60 K, isolated water molecules will stay put when you place them on a metallic substrate. At higher temperatures, the molecules become mobile enough to begin forming into tiny islands of two-dimensional ice. New molecules landing on the crystallites will fall off the edges into the spaces between the islands. In this way the metal surface becomes iced over completely with a monolayer. But because the water molecules' four bonds are now spoken for (1 to the Pt substrate and 3 to their neighboring water molecules), the addition of more water does not result in layer-by-layer 3D ice growth. Only when there is an amount of overlying water equivalent to about 40 or 50 layers does 3D crystalline ice completely cover the hydrophobic monolayer. The PNL researchers (contact Greg Kimmel, 509-376-2501, gregory.kimmel@pnl.gov) are the first to observe this effect. For the novel hydrophobic property to show itself, the water-substrate bond has to be strong enough to form a stable monolayer. Weaker bonding results in a "classic" hydrophobic state, in which the water merely balls up immediately; in other words, not even a first monolayer of ice forms. This research should be of interest to those who, for example, study the seeding of clouds, where ice is nucleated on particles in the atmosphere.

Kimmel et al., Physical Review Letters, upcoming article