Supermuscles made of nanotubes
Superkiborg MusclesArtem Tuntsov, "Newspaper.
The first one could well survive in molten iron, and the second one could not crumble into small fragments under a shower of liquid nitrogen.
A group of scientists from the Institute of Nanotechnology at the University of Texas at Dallas has created an amazing material that can be used to create artificial muscles.
A tape made of multi-walled carbon nanotubes is tougher than steel, more elastic than rubber, capable of expanding and contracting in milliseconds, transparent, conducts current well and works excellently in the temperature range from -200 to +1600 Celsius.
And perhaps even at more extreme temperatures. These limits are the limits within which the authors of the work published in today's issue of Science were able to verify the properties of the material. Among the authors of the work there are many scientists with Russian surnames, and the research is led by Professor of chemistry at the University of Texas, director of the University Institute of Nanotechnology Ray Bomen, who turned out to be a foreign member of the Russian Academy of Sciences, which once again confirms that it is not the place that makes a person beautiful, but just the opposite.
Making miracle tapesTo get strips of aerogel, scientists first grow a "forest" of multi-walled carbon nanotubes on a special substrate, and then drag some of them behind an adhesive tape.
Other nanotubes cling to each of the enthusiastic ones. As a result, most of the tubes are stretched in one direction, although not perfectly – somewhere they are intertwined, somewhere they stand in a raskoryak, connecting longer fibers. Such tapes can be "woven" with a capacity of more than 2 meters per second.
The new material is an aerogel made of multilayer carbon nanotubes, that is, a substance, most of the volume of which is occupied by air. Thanks to this, the tapes made of it are almost weightless: a cubic meter of air weighs 1.2-1.3 kg, and a cubic meter of aerogel would weigh 1.5 kg if it occurred to someone to synthesize so much of this material. While it is synthesized in strips 0.05 millimeters thick, a few centimeters wide and a meter long; only 3 grams of such ribbons can cover a hundred acres of land. The remaining 200-300 grams per cubic meter, which Archimedes' force does not compensate for, are carbon nanofibers, similar to rolls of garden netting, only not with diamond–shaped, but hexagonal cells, in the tops of which carbon atoms sit; on average, there are 9-10 layers of "mesh" in each roll.
It seems that the new material has amazing and often unique mechanical properties.
You can start with anisotropy – differences in mechanical properties in different directions. According to John Madden from the University of the Canadian Province of British Columbia, who wrote a comment to the article by Bohman and colleagues for Science, this aerogel "feels like a diamond on the one hand and rubber on the other." In the longitudinal direction (in which the nanotubes are oriented), it is almost impossible to compress aerogel by more than a few percent, and in the transverse direction it compresses better than the softest rubber.
However, to say that it is "stronger than steel" is deceit. In this case, we mean the specific stiffness per unit mass. Being 5 thousand times less dense than steel, aerogel is significantly inferior to metal when comparing samples of the same volume – even if the tape is compressed 400 times in thickness (as Texas scientists have shown, while its mechanical properties do not change in other directions). Nevertheless, exceptional specific rigidity is a big plus, for example, for space applications, where each gram of equipment put into orbit can cost thousands and thousands of dollars.
The material also has one more amazing property: it becomes denser when you stretch it along the length of the tape, and less dense when you squeeze it in the same direction. The Poisson's ratio, which shows how much percent the substance expands to the sides when you compress it along by 1%, is about 15 for aerogel, while for ordinary substances it cannot exceed 0.5. Unlike all other materials, at the bottom of the Mariana Trench, under enormous pressure, uniformly applied from all sides, the cylinder of aerogel would become not shorter, but longer.
But the most interesting thing, of course, is its electromechanical properties, which allow us to hope for use as "artificial muscles" for robots.
If a high voltage is applied to the tape relative to the "ground", it expands strongly and almost instantly – in milliseconds – in transverse directions. For example, if the potential on the tape is 4 kV, it swells almost twice in width and almost three times in thickness. This is due to the mutual electrostatic repulsion of nanotubes, on which, at such a voltage, there are exceptionally many "extra" electrons.
At the same time, during this charging, the material is slightly compressed, by a fraction of a percent, in the longitudinal direction, which is again associated with an abnormally high Poisson's ratio. At the same time, a huge force develops. If we use films compressed hundreds of times (this, as we remember, does not change the mechanical and electromechanical properties), aerogel turns out to be 30 times stronger than biological muscles.
Roughly speaking, if you can lift 150 kg lying down with your own hands, then you could squeeze 5 tons out of "aerogel" muscles with the same hands.
However, due to the enormous rigidity of the material, this force means very little movement: you could lift 5 tons not by a meter, but only by a few centimeters. In operation, aerogel gives only about 30% of the gain against real, live muscles. But, given its ability to carry out thousands of cuts per second, the gain in power can be tens or hundreds of times.
But no one is going to use this material in prostheses and transplants yet – after all, the kilovolts necessary for work are in no way similar to the activation potentials of muscles in living organisms. And scientists are not really thinking about robots yet. According to them, a transparent, conductive, lightweight aerogel with very unusual properties is more likely to find its first use as electrodes for organic light-emitting diodes, solar panels and similar materials. But what the hell is not joking.
Portal "Eternal youth" www.vechnayamolodost.ru20.03.2009