Nanotechnology-based flexible actuators
In 'Nanotube paper flexes on demand,' nanotechweb.org reports that French researchers are using multiwalled carbon nanotubes (MWCNTs) reinforced with polyvinyl alcohol (PVA) to develop ultra-lightweight actuators for aerospace applications. The scientists have developed a paper-like sheet which bends when the material is electrically stimulated. As said one of the lead researchers, 'The porous nature of the CNT-PVA composite allows the ions of the liquid electrolyte to enter and swell the film when the device is electrically stimulated. The system expands at both positive and negative voltages, but the expansion is more pronounced when we apply a negative voltage.' Besides aerospace applications, these findings could be used for robotics or in automotive systems. But read more...
You can see on the left a photo of one of the researchers, Christèle Bartholome, preparing an oxidized-MWCNT material. (Credit: CNRS/nanotechweb; link to a larger version) Bartholome works at the Centre de Recherche Paul Pascal, located near Bordeaux, France. She is a member of the molecular organized materials group working on carbon nanotubes. The other researchers involved inthis project are Alain Derré, Olivier Roubeau, Cécile Zakri and Philippe Poulin.
Here is a short explanation of what achieved the research team. "The researchers first oxidize a sample of MWCNTs, which encourages the structures to bind strongly with the host polymer. Next, the nanomaterial is dispersed in water and then mixed with various amounts of high molecular weight PVA. Membrane filtration is used to remove the water and shape the remaining materials into a paper-like sheet. A gold layer is then deposited over the CNT-polymer surface, which helps to distribute charge evenly throughout the film and promotes uniform actuation. Finally, an insulating and inert polymer layer is added on the reverse side to complete the bimorph device.
And here is another quote from Bartholome. "Materials comprised solely of nanotubes exhibit a high electrical conductivity, but are too weak to effectively convert electrical energy into mechanical energy. By adding an optimal fraction of polymer binder, we can strengthen the CNT assembly and still obtain a structure that is a sufficiently porous and electrically conductive network to swell when stimulated in an electrolyte."
This research work has been published by Nanotechnology, a scientific journal published by the Institute of Physics in the UK under the title "Electromechanical properties of nanotube-PVA composite actuator bimorphs" (Volume 19, Number 32, Article 325501, August 13, 2008).
Here is an excerpt from the abstract. "Oxidized multiwalled carbon nanotube (oxidized-MWNT)/polyvinyl alcohol (PVA) composite sheets have been prepared for electromechanical actuator applications. MWNT have been oxidized by nitric acid treatments. They were then dispersed in water and mixed with various amounts of PVA of high molecular weight (198 000 g mol-1). The composite sheets were then obtained through a membrane filtration process. The composition of the systems has been optimized to combine suitable mechanical and electrical properties. Thermogravimetric analysis, mechanical tensile tests and conductivity measurements show that the best compromise of mechanical and electrical properties was obtained for a PVA weight fraction of about 30%."
This research work has been done for a EU-funded project named NOESIS. Its goal is to develop aerospace nanotube hybrid composite structures with sensing and actuating capabilities. This project started in April 2005 and should be completed in March 2009. The total budget is €5 million with a EU-backing of €3 million.
Here are the goals of the NOESIS project. "The increased use of high performance composites as structural materials in aerospace components is continuously raising the demands in terms of dynamic performance, structural integrity, reliable life monitoring systems and adaptive actuating abilities. This project will exploit the unique properties of Carbon Nanotubes (CNTs) as a matrix dopant in Fibre Reinforced Plastics (FRP), with the aim of producing structural composites with improved mechanical performance as well as sensing/actuating capabilities.The development of new generation composites using CNTs as filler material within the matrix is expected to result in the enhancement of the damping properties of the material, the increased fracture toughness and the improvement of its fatigue life. This is expected to occur due to the multiplicity of energy dispersive mechanisms within the material.
Sources: James Tyrrell, nanotechweb.org, September 11, 2008; and various websites
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