Nano-actuators
Nano-actuators and motors will be crucial in future micro machines and are already being employed in zoom lenses for digital cameras and vibration alerts for mobile phones, to name but two examples. Still actuators made on the nanoscale poses a challenge because such conventional devices are too complex to easily downsized, boot and poorly. Available torsional artificial-muscle systems are based on ferroelectrics, shape-memory alloys or conducting organic polymers.
Carbon nanotube muscle
Researchers of University of Wollongong in Australia have made an artificial muscle using carbon nanotube threads. The new structure can twist and turn very quickly compared to previously made devices. The muscles are composed of thin carbon nanotube threads. Carbon nanotubes are hollow cylinders of rolled up carbon. For making the torsional structures the carbon nanotubes are to be twisted as they are made into a thread to produces a helical structure of intertwined carbon nanotubes.
Researchers in the US A have made artificial muscle made from carbon nanotubes. The muscles flex when electrically charged and can expand to 220% of their original length in a matter of milliseconds. The devices could find use in medical and aerospace applications, and perhaps even in robots of the future.
Fabrication
Lengths of the nanotube thread are taken, partially immersed in an electrically conducting liquid or electrolyte, both ends of tubes held firmly and one end is connected to a low-voltage battery. When the voltage is applied, the thread absorbs some of the liquid and swells up. The pressure subsequently produced by the swelling causes the twisted structure to partially unwind, creating a rotating action similar to that seen when stretching a helical spring. Thus a twisting motion is observed in the nanotube. The structure can be made to rotate in the opposite direction by decreasing the applied voltage.
Applications
The new muscle-like structures will be important for applications that require mechanical movement and where volume is limited and they could find their way into a host of application areas, including micro fluidics, valves and robotics. By charging the thread with just a few volts of electricity the threads are found strong enough to hold large weights of nearly 2000 times heavier than the thread itself. Carbon nanotubes, which are normally stiff and strong and that have been made more flexible by spinning them into yarns, are ideal for making such muscle-like structures because they have good electrical conductivity. The muscles made by researchers of US A might be used as actuators in medical and other devices, as well as in electrodes for solar cells, light-emitting diodes and displays. They might also find their way into future robot arms and legs.