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Physical Chemistry

Microrockets Take Off In Acid

Scientists adapt tiny polymer-coated metal engines to use acid as fuel, enabling them to function in extreme environments

by Lauren K. Wolf
January 16, 2012 | APPEARED IN VOLUME 90, ISSUE 3

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Credit: J. Am. Chem. Soc.
An acid-propelled microrocket (left) moves at about 500 μm per second in 1 M HCl, leaving a trail of H2 bubbles behind (right).
09003-scicon-microrocket.jpg
Credit: J. Am. Chem. Soc.
An acid-propelled microrocket (left) moves at about 500 μm per second in 1 M HCl, leaving a trail of H2 bubbles behind (right).
ACID POWER
Credit: J. Am. Chem. Soc./C&EN/YouTube
In this clip, microrockets zoom through various strong acids and pick up, transport, and release a magnetic polystyrene microbead.

Microrockets—those tiny, self-propelled, tubular engines being developed to pick up and carry cellular and molecular cargo—can now operate in some natural environments (J. Am. Chem. Soc., DOI: 10.1021/ja210874s). With existing versions, researchers add hydrogen peroxide fuel to a solution containing microrockets to get the tiny engines to zoom along; H2O2 reacts on the rocket’s inner platinum surface to form oxygen bubbles that push the tube through solution. A team led by Joseph Wang of the University of California, San Diego, has now developed microrockets that use strong acids—already present in extreme environments such as the stomach—as fuel. The new versions have a tubular zinc core and an outer layer of polyaniline. The zinc reduces acids to produce hydrogen bubbles, which serve as the propellant. The researchers showed that the speed of the acid-fueled rockets depends on solution pH and that by adding layers of titanium and nickel to the outside of the tubes they can control rocket motion with a magnetic field. Wang says his group will be working on extending the lifetime of the rockets, which are currently consumed by strong acid after two minutes.

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