Forcing Water Uphill

Can water fight the forces of gravity and flow uphill?

The answer, according to a group of Harvard chemists, is a qualified "yes." In a collaborative effort, Mallinckrodt Professor of Chemistry George M. Whitesides '60 and Manoj K. Chaudhury of Dow Corning showed that water, pulled by a chemical gradient, can indeed travel upwards on a surface.

According to Hans Biebuyck, a chemistry graduate student who works in the Whitesides group, the only ingredient missing from nature was an impetus for water to move.

This impetus, Whitesides and Chaudhury found, could be provided chemically by molecules whose properties determine the nature of a surface.

In a series of simple experiments which lasted just two weeks, scientists created a silicon surface which was hydrophobic, or water-resistant, at one end and hydrophilic, or attracted to water, at the other. When a drop of water was placed on the titled surface with the hydrophilic end up, the drop "climbed" the hill.

The water's flow, Biebuyck says, is analogous to the movement of molecules across the lipid membranes of human cells. Such membranes are sprinkled with proteins which are hydrophobic on one end and hydrophilic on the other, like the configuration of the silicon surface.

Following through on this analogy, says Biebuyck, the uphill flow provides a simple model which could be useful in clarifying the intricacies of complex biological systems.

In addition, the model may be useful for developing systems in which humans can control how objects move across a surface. For example, scientists have imagined a new type of computer which functions according to principles of surface chemistry. Described by Biebuyck as "wildly speculative," the prototype computer would be driven by chemicals rather than electricity, reducing costs and also the risk of breakdowns.

The Whitesides lab, which focuses its studies on the structure and function of interfaces, has been examining the movement of water on various surfaces for more than six years.