Researchers have discovered that ordinary cellulose is a piezoelectric and smart material that can flap when exposed to an electric field. ScienceNOW reports that electricity can give life to cellophane. When you put a very thin layer of gold on each side of cellophane, and that you apply electric current to the gold layers, one positive, one negative, the cellophane curved toward the positive side. If you switch the voltage fast enough, the cellophane starts to act as a wing. So it should be possible to use it to build lightweight flying robots carrying cameras, microphones or sensors for surveillance missions. But read more...
And here is how ScienceNOW describes what he did with his team.
They took cellophane, a lightweight paper made of cellulose, and deposited a very thin layer of gold on each side. The gold layers were connected to a voltage and acted as electrodes, with one side of the paper positive and the other negative.
When the voltage was turned on, the cellophane curved toward the positive side; when the voltage was switched, the paper bent to the other side. If switched rapidly, the paper could "flap" like a wing. Wires aren't necessary, because the cellulose is sensitive enough to be controlled by microwaves (an antenna converts them into dc current).
In a recent press release, the American Chemical Society (ACS) added that smart cellulose may mean paper airplanes that fly like butterflies (June 26, 2006).
Kim's group terms smart cellulose "electroactive paper" (EAPap), a chemically treated paper with thin electrodes on both sides. When electrical voltage is applied on the electrodes, the EAPap bends. No wires or batteries are needed because a special microstrip antenna and other lightweight electronic components can be integrated into the EAPap. Radio waves beamed to the antenna then would be converted into electricity that moves the EAPap.
Below is a picture of the EAPap in its original state (Credit: Jaehwan Kim, Inha University, via New Scientist).
And here you can see the effect of the application of an electric field to this smart paper (Credit: Jaehwan Kim, Inha University, via New Scientist).
So what could we do with such a smart paper? ScienceNOW writes that it "could be used to make microrobots, biodegradable sensors, and paper airplanes that flap like birds."
But in Smart paper may put lightweight spies in the skies, New Scientist goes further (June 12, 2006).
The material raises the prospect of swarms of tiny lightweight aircraft carrying sensors that act as the eyes and ears of a surveillance network.
"This new material opens up a whole range of possible applications," says Djamel Azzi, a robotics researchers at Portsmouth University, UK. "Lightweight flying robots would be ideal for surveillance -- they could carry cameras, microphones or other sensors around."
For more information, this research was published by the ACS journal Macromolecules under the title "Discovery of Cellulose as a Smart Material" (Vol. 39, No. 12, Pages 4202-4206, June 27, 2006). Here are two links to the abstract and to the full paper (PDF format, 5 pages).Here are the conclusions of this paper.
We reported the discovery of cellulose paper as a smart material by demonstrating a EAPap bending actuator that exhibted a large displacement, low actuation voltage, and low electrical power consumption. We note that the cellulose-based EAPap material has recrystallized in the presence of electric field in such a way that the material exhibits enhanced bending actuation.
The recrystallization happens mostly in the disordered region of cellulose. By combining piezoelectricity of cellulose and ionic transport, this oriented EAPap material will enable inexpensive and lightweight biomimetic actuators and MEMS devices. Cellulose-based EAPap material is also promising as biosensors since it is biodegradable, biocompatible, sustainable, and capable of broad chemical modification and has high mechanical stiffness and strength.
Control of disordered region, recrystallization, and orientation of cellulose are all issues that need to be addressed in order for cellulose EAPap to fulfill its promise as a smart material.
After reading these conclusions, I sure feel happy that the nice guys at ScienceNOW and New Scientist 'translated' the paper for me.
Sources: Kim Krieger, ScienceNOW, June 29, 2006; and various web sites
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