OT: Synthetic Tree May Lead To Technologies For Heat Transfer, Soil Remediation

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World's First Synthetic Tree: May Lead To Technologies For Heat

Transfer, Soil Remediation

 

http://www.sciencedaily.com/releases/2008/09/080910161900.htm

 

ScienceDaily (Sep. 11, 2008) — In Abraham Stroock's lab at Cornell,

the world's first synthetic tree sits in a palm-sized piece of clear,

flexible hydrogel -- the type found in soft contact lenses.

 

Stroock and graduate student Tobias Wheeler have created a " tree "

that simulates the process of transpiration, the cohesive capillary

action that allows trees to wick moisture upward to their highest

branches.

 

The researchers' work, reported in the Sept. 11 issue of the journal

Nature, bolsters the long-standing theory that transpiration in trees

and plants is a purely physical process, requiring no biological

energy. It also may lead to new passive heat transfer technologies

for cars or buildings, better methods for remediating soil and more

effective ways to draw water out of partially dry ground.

 

Of course, the synthetic tree doesn't look much like a tree at all.

It consists of two circles side by side in the gel, patterned with

evenly spaced microfluidic channels to mimic a tree's vascular system.

 

In nature, trees use water in tubular tissues, called xylem, like

ropes that pull more water out of the ground, delivering it to

leaves. They manipulate the water in the xylem under negative

pressure -- what's called a metastable liquid state -- right on the

verge of becoming a vapor.

 

Xylem-like capillaries are relatively easy to create by

microfabrication, but the researchers' choice of a material to act as

membranes in the leaf and root to separate the liquid from the

atmosphere and the soil was much trickier.

 

Stroock, assistant professor of chemical and biomolecular

engineering, and Wheeler, a graduate student in his lab, used pHEMA

hydrogel, or polyhydroxyethyl methacrylate, to form the plant

membranes. The hydrogel is a solid embedded with water and has

nanometer-scale pores. The material acts as a wick by holding liquid

in the pores, through which capillary action creates tension in the

water.

 

By building mimics of xylem capillaries within the gels, the

scientists were able to create negative-pressures of the magnitude

observed in trees, and to pump water against large resistances and

out of subsaturated, or partially dry, sources.

 

Besides supporting the theory of transpiration as a physical, not

biological, process, the synthetic tree also introduces a new way to

study water under tension -- a subject interesting to physicists and

chemists. Many questions about the metastable state of water could be

answered using this new " tree. "

 

" Water is the most studied substance on Earth, and yet there is a big

metastable region in its phase diagram waiting to be characterized, "

Stroock said. His lab is pursuing these studies with support from the

National Science Foundation.

 

The capillary action used in trees might be applicable to developing

new passive heat-transfer methods, Stroock said. The heat-transfer

technology commonly used for cooling laptops, which uses vaporization

to carry the heat to the fan on the edge of the computer, could be

scaled up using the technology developed for the synthetic tree.

 

" It would be nice if you could, in a building, put these passive

elements that carry heat around very effectively, for example, from a

solar collector on the roof, to deliver heat all the way down through

the building, then recycle that fluid back up to the roof the same

way trees do it -- pulling it back up, " Stroock said.

 

He also envisions the synthetic tree helping to build better soil

remediation systems. Instead of having to soak contaminated soil to

pump contaminants out, transpiration could help pull the contaminated

fluid out of the soil without the use of more liquid. Similarly, the

technology could also be used to draw water out of relatively dry

soil without having to dig a well down to the water table.

 

Adapted from materials provided by Cornell University. Original

article written by Anne Ju.

 

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Cornell University (2008, September 11). World's First Synthetic

Tree: May Lead To Technologies For Heat Transfer, Soil Remediation.

ScienceDaily. Retrieved September 25, 2008, from

http://www.sciencedaily.com­ /releases/2008/09/080910161900.htm