Counterintuitive Compound CreatedCategory: Science & Technology
Posted: May 24, 2012 04:45PM
Throughout life we learn that certain actions and situations cause certain reactions, but occasionally we find exceptions. With enough thrust what goes up need not come down, and under the proper circumstances, water can be made to flow up hill. Researchers at Northwestern University have made a new exception by creating a metamaterial that expands when compressed and contracts when tensioned.
Every natural material acts like a rubber band in that when you pull on the band, it stretches out and becomes longer. A band made out of this material will do the opposite though, as it will shorten as you pull on it. If you try to squeeze it into a smaller shape though, it will actually expand in response. Also, it does not take much energy to get this to happen as it exhibits force amplification, where a small deformation triggers a larger response.
Obviously the question is, "how?" It turns out the physics involved does not say a material cannot contract when you pull on it, just that the effect cannot be continuous. The researchers decided to use phase transitions to make the seemingly opposite response occur discontinuously. The result is what the researchers call 'negative compressibility transitions,' and there are potential uses for this. Actuators and potentially some protective devices may be able to take advantage of the negative compressibility while micromechanical devices and ratchets can utilize the force amplification property.