http://www.eapap.com
http://www.technologyreview.com/articlefiles/17127-bourzac 070706
Friday, July 07, 2006

Moving Paper Parts for Robots

Cellulose films could provide flapping wings and cheap artificial muscles for robots.

by Katherine Bourzac

( This thin film of gold-coated cellulose flaps like dragonfly wings in response to an electrical current. The material, called electroactive paper, may serve as wings for small flying robots. (Courtesy of Zoubeida Ounaies, Texas A&M University. )

Researchers at Inha University in South Korea have demonstrated that cellulose, the main ingredient in paper, can bend in response to electricity. The treated cellulose is lightweight, inexpensive, and has low power requirements, compared with similar electrically active materials. The Korean researchers are now working with NASA to develop insect-sized, wirelessly powered flying vehicles with flapping paper wings. Such vehicles could fly into areas unsafe for humans and test for hazardous gases -- or survey the surface of Mars from the air.

The researchers, led by Jaehwan Kim (http://www.eapap.com ) , associate professor at the university, made the electrically active cellulose by dissolving paper pulp, forming it into sheets, and coating it with a layer of gold as an electrode. Some areas of the cellulose film are highly ordered, while in other areas, the cellulose strands are tangled like spaghetti. The movement of ions through the paper -- and the movement of cellulose strands themselves, which have negative and positively charged ends -- causes the paper to bend in response to an electrical current. The bending is driven by the ordered regions, but free space in disordered regions allows ions to flow more freely and adds to the paper's ability to deform.

Materials that move in response to electrical current are called piezoelectrics. Kim's cellulose is one of a new class of these materials, called electroactive polymers, that have generated excitement in the scientific community for their potential uses in many areas: artificial muscles, chemical sensors, visual displays, the moving parts of robots, and batteries.

"The value of electrically active paper is that it's lightweight and has a high deflection [movement] at low voltage" compared to traditional electroactive polymers, says Sang Choi, senior research scientist at the NASA Langley Research Center. When a small voltage is applied to Kim's paper, it can move a relatively large distance; for instance, in experiments, the tip of a 30-millimeter-long strip of electroactive paper was displaced 4.2 millimeters. Indeed, the strength of the electric field required to move the tip of the paper to its maximum displacement is one to two orders of magnitude less than is required by other electroactive polymers. And the paper can change shape quickly, moving back and forth as fast as once every 0.06 seconds.

NASA's Choi is interested in Kim's material because, compared with conventional piezoelectrics and other electroactive polymers, it is very lightweight and requires very little power. Together, Choi and Kim are designing a small flying vehicle with cellulose wings powered by ambient microwaves. Choi says NASA expects such robots to play an important role in its long-term exploratory missions. For example, small robots with moving parts made of paper or other materials might fly low over the Martian surface to monitor its topology. Still, it's not clear that cellulose can withstand the extreme conditions in outer space. ---

Abstract --- A film structure of a ferroelectric single crystal which can be beneficially used in the fabrication of high-performance electric and electronic parts and devices is prepared by forming an electrode layer having a perovskite crystal structure on a substrate made of a silicon or ferroelectric single crystal optionally polished to have a off-axis crystal structure, and epitaxially growing a layer of a ferroelectric single crystal thereon by pulsed laser deposition (PLD) or metallorganic chemical vapor deposition (MOCVD).

Center for EAPap Actuator, Department of Mechanical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon 402-751, South Korea
email: Jaehwan Kim (jaehwan@inha.ac.kr)

*Correspondence to Jaehwan Kim, Center for EAPap Actuator, Department of Mechanical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon 402-751, South Korea. Fax: (+82) 32 868 1716

Abstract --- This paper introduces an electroactive paper (EAPap) prepared with cellulose and chitosan films. The fabrication process, performance test, and the effect of acetic acid dosage of the EAPap were investigated. For the fabrication of cellulose EAPap, cellulose fibers were dissolved into a solution using N,N-dimethylacetamide and lithium chloride. The solution was cast and immersed in water to form a cellulose film, followed by casting chitosan/acetic acid and glycerol aqueous solutions on the cellulose film. A bending EAPap actuator was made by depositing thin gold electrodes on both sides of the cellulose film. The bending displacement of the EAPap actuators was evaluated with respect to voltage, frequency, humidity, and acetic acid dosage. An optimum mole ratio of the acetic acid and chitosan structure unit was found. Also, the effects of chitosan and acetic acid on the actuation behavior of the cellulose-chitosan laminated films were investigated.

1Center for EAPap Actuator and Department of Mechanical Engineering, Inha University, Incheon 402-751, South Korea
2National Chemical Laboratory, Chemical Engineering Division, Pune - 41108, India
email: Jaehwan Kim (jaehwan@inha.ac.kr)
*Correspondence to Jaehwan Kim, Center for EAPap Actuator, Department of Mechanical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Gu, Incheon 402-751, South Korea

Abstract -- This investigation deals with the synthesis, characterization and actuation behavior of conductive polyaniline-coated electroactive paper actuators. The actuator is made by electrochemical deposition of conductive polyaniline on a cellulose paper. The aim of the investigation was to improve the bending displacement of electroactive paper actuators. The displacement outputs of the actuators show that a trilayer is better than a bilayer configuration. The nature of the dopant ion used in the electro-generation affects the performance. A change in humidity plays a vital role in actuation performance of the actuators. Comparing the performance of electroactive paper actuators with and without a conductive polyaniline coating, the coating improves the displacement output threefold. Finally, the actuation principle mechanism is addressed.

Paper aeroplanes could fly by flapping their wings thanks to smart paper that bends when bathed in an electric field. The material raises the prospect of swarms of tiny lightweight aircraft carrying sensors that act as the eyes and ears of a surveillance network.

Electroactive paper (EAPap) is ordinary cotton-based paper, similar to the material used to make US bank notes, coated on each side with a thin layer of gold. The smart paper has been made by researchers from Inha University, South Korea, and Texas A & M University, US

Unlike ordinary paper, EAPap bends as a result of two effects working together. When a voltage is applied, the gold coating on one side of the paper becomes a positively charged while the other side becomes negatively charged. Sodium ions in the paper move towards the negative electrode, taking water molecules with them. This makes that side of the paper expand, causing it to bend.

At the same time, the paper's matrix of cellulose fibres have piezoelectric properties and change shape when a voltage is applied. This increases the bending. The research team have even improved the paper's piezoelectric properties even further by adding carbon nanotubes to the paper mix.

Artificial muscle

The team has made strips of paper 40 millimetres long and 0.3 mm thick that bend by 10 mm, producing a force of more than 10 micronewtons. That is enough to lift about 1 gram.

"This new discovery of cellulose paper as a smart material gives us a lot of possibilities that we can play around with," Jaehwan Kim, who researches smart materials at Inha University.

Kim's team is interested in using the material as a kind of artificial muscle for mobile robots. He hopes to power the robots remotely by fitting them with a simple electronic device called a "rectenna". This converts the energy of a microwave beam into a small voltage.
Flying sensors

"A normal paper aeroplane just flies as it is," says Jaehwan Kim. "By sending microwaves we could control its wings and make it glide in a certain path."

Another possibility is a robot in the form of a rippling sheet of EAPap that crawls along the ground. As well as working on boosting the power of EAPap, the Korean team is collaborating with NASA to develop the rectenna system to drive it.

"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."

Cellulose based Electro-Active Paper (EAPap) has been reported as a smart material that has merits in terms of lightweight, dry condition, biodegradability, sustainability, large displacement output and low actuation voltage. However, its actuator performance is sensitive to humidity: its maximum bending performance was shown at high humidity condition. To overcome this drawback, we introduce an EAPap made with cellulose and chitosan blend. Cellulose-chitosan blend films with varied mixing ratio were prepared by dissolving the polymers in trifluoroacetic acid as a co-solvent followed by spincoating onto glass substrates. A bending EAPap actuator is made by depositing thin gold electrodes on both sides of the cellulose-chitosan films. The performance of the EAPap actuator is evaluated in terms of free bending displacement with respect to the actuation frequency, activation voltage, humidity level and content of chitosan. The actuation principle is also discussed.

(1) Creative Research Center for EAPap Actuator, Mechanical Engineering Department, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon, 402-751, South Korea

Received: 11 July 2006 Accepted: 10 January 2007 Published online: 14 February 2007
Abstract In an earlier work we reported the discovery of cellulose as a smart material that can be used in sensors and actuators. While the cellulose-based Electro-Active Paper (EAPap) actuator has many merits – lightweight, dry condition, biodegradability, sustainability, large displacement output and low actuation voltage – its performance is sensitive to humidity. We report here on an EAPap made with a cellulose and sodium alginate that produces its maximum displacement at a lower humidity level than the earlier one. To fabricate this EAPap, we dissolved cellulose fibers into a aqueous solution of NaOH/urea. Sodium alginate (0, 5 or 10% by weight) was then added to this cellulose solution. The solution was cast into a sheet and hydrolyzed to form a wet cellulose-sodium alginate blend film. After drying, a bending EAPap actuator was made by depositing thin gold electrodes on both sides of it. The performance of the EAPap actuator was then evaluated in terms of free displacement and blocked force with respect to the actuation frequency, activation voltage and content of sodium alginate. The actuation principle is also discussed.

(1) Center for EAPap Actuator, Department of Mechanical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon 402-751, COREE, REPUBLIQUE DE

Abstract -- This paper introduces an electroactive paper (EAPap) prepared with cellulose and chitosan films. The fabrication process, performance test, and the effect of acetic acid dosage of the EAPap were investigated. For the fabrication of cellulose EAPap, cellulose fibers were dissolved into a solution using N,N-dimethylacetamide and lithium chloride. The solution was cast and immersed in water to form a cellulose film, followed by casting chitosan/acetic acid and glycerol aqueous solutions on the cellulose film. A bending EAPap actuator was made by depositing thin gold electrodes on both sides of the cellulose film. The bending displacement of the EAPap actuators was evaluated with respect to voltage, frequency, humidity, and acetic acid dosage. An optimum mole ratio of the acetic acid and chitosan structure unit was found. Also, the effects of chitosan and acetic acid on the actuation behavior of the cellulose-chitosan laminated films were investigated.

1 Creative Research Center for EAPap Actuator, Mechanical Engineering Department, Inha University, Incheon 402-751, Korea
2 National Chemical Laboratory, Chemical Engineering Division, Pune-41108, India
3 Author to whom any correspondence should be addressed
E-mail: jaehwan@inha.ac.kr

Abstract -- Actuators based on cellulose paper with conducting polymer (CP-EAPap) as an electrode material were constructed. The bilayer and trilayer types of actuators were fabricated by depositing conducting polypyrrole on one side and two sides of cellophane paper respectively, which was previously gold coated. By varying the deposition time, the electrode thickness was manipulated. The performance of these two types of actuators was compared with respect to humidity changes and thickness variation. The electrode thickness plays a key role in the displacement behavior of these types of actuators. The best performance at higher humidity is also characteristic of CP-EAPap actuators. The possible mechanism of actuation is addressed in this paper.

Abstract -- In an earlier work we reported the discovery of cellulose as a smart material that can be used in sensors and actuators. While the cellulose-based Electro-Active Paper (EAPap) actuator has many merits - lightweight, dry condition, biodegradability, sustainability, large displacement output and low actuation voltage - its performance is sensitive to humidity. We report here on an EAPap made with a cellulose and sodium alginate that produces its maximum displacement at a lower humidity level than the earlier one. To fabricate this EAPap, we dissolved cellulose fibers into a aqueous solution of NaOH/urea. Sodium alginate (0, 5 or 10% by weight) was then added to this cellulose solution. The solution was cast into a sheet and hydrolyzed to form a wet cellulose-sodium alginate blend film. After drying, a bending EAPap actuator was made by depositing thin gold electrodes on both sides of it. The performance of the EAPap actuator was then evaluated in terms of free displacement and blocked force with respect to the actuation frequency, activation voltage and content of sodium alginate. The actuation principle is also discussed.

K. Y. Cho, H. G. Lim, S. R. Yun, Jaehwan Kim, and K. S. Kang*
Creative Research Center for Electroactive Paper (EAPap) Actuator, Mechanical Engineering Department, Inha University 253 Yonghyun-Dong Nam-Ku 402-751, Incheon, South Korea
J. Phys. Chem. C, 2008, 112 (17), pp 7001–7004

To whom correspondence should be addressed. E-mail: kkang@ inha.ac.kr.

Abstract -- The causes of Au-electrode damage to an electroactive paper (EAPap) actuator coated with Au and polypyrrole (PPy) were investigated with various electric field frequencies and strengths. The resonance frequency of 3.5 Hz was obtained for 3 and 4 V. Electric field frequencies below (2 Hz) the resonance frequency yielded a faster bending displacement reduction than those of the higher resonance frequency. High electric field strength (4 V) shows a faster reduction of bending displacement than lower field strength (3 V). The degree of Au-electrode damage after a certain period of actuation is shown in field emission scanning electron microscope (FESEM) images. The electric field strength and frequency and bending displacement reduction were found to be closely related to the degree of Au-electrode damage.

Creative Research Center for ElectroActive Paper Actuator, Mechanical Engineering Department, Inha University, 253 Yonghyun-Dong Nam-Ku, 402-751 Incheon, ...

2009 Smart Mater. Struct. 18 015003 (5pp) doi: 10.1088/0964-1726/18/1/015003
Sang-Dong Jang, Joo-Hyung Kim1, Cai Zhijiang and Jaehwan Kim
Creative Research Center for EAPap Actuator, Department of Mechanical Engineering, INHA University, 253 Young-Hyun Dong, Nam Gu, Incheon 402-751, Korea
E-mail: joo-hyung.kim@inha.ac.kr

Abstract -- We studied the effect of chitosan blending on the electrical property of chitosan-blended cellulose electroactive paper (EAPap) under different humidity conditions. As the chitosan blending ratio increased, the real part of the dielectric constant of chitosan-blended cellulose EAPap increased while the dielectric loss factor decreased. From the curve fitting of the measured data using an electrode polarization model, it was found that increasing the chitosan ratio in the EAPap might promote a decrease in the relaxation time of the EAPap, resulting in an increase of the ion mobility and dc conductivity. Over 30% of the chitosan blending ratio, a gradual increment of the ion mobility of the EAPap was observed at 40% relative humidity, while a quadratic increment of the mobility was found at 60% relative humidity condition. This kind of ion-mobility-enhanced cellulose EAPap can be used not only for bending actuators but also for medical applications such as blood clotting patches.