This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In their earliest years of development, computers used mechanical gears and levers to store information. Today, researchers are exploring whether a material itself can hold onto information, storing memory in how it bends and springs back to its original shape.
Through new research published in Physical Review X, Ramathasan Thevamaran and colleagues at the University of Wisconsin–Madison have discovered a material that takes this concept a step further: a foam made of carbon nanotubes that remembers exactly how hard it was squeezed, then returns to its original shape with no lasting damage. In computers with built-in mechanical memory, many researchers hope devices could function without batteries or chips. So far, most designs have focused on "bistable" structures: tiny components that snap between just two shapes, like a switch flicking on or off.
This gives a simple form of memory but only gives the system two states to work with. While more continuous memory-like behavior can be found in other materials, they tend to permanently deform and degrade with age or may require special training before they can perform reliably. Key to solving these challenges will be a material that remembers its original shape while still bouncing back elastically and undamaged every time.
To search for such a material, Thevamaran's team turned to foams made of vertically aligned carbon nanotubes. They repeatedly compressed the foam until its response stabilized, then tracked how it behaved under partial unloading and reloading. The foam displayed "return-point memory": When pushed partway, released, then pushed again, it returns to the exact mechanical state it was in before.
The behavior is directly comparable to magnetic hard drives, where reversing a magnetic field brings the material back to a previously recorded state. Crucially, the nanotube foam didn't relax or fade over time as conventional materials do. The team traced the effect to friction at the nanoscale: Neighboring nanotubes repeatedly stick and slip against each other as the foam compresses.
Rather than permanently stretching or breaking the material, this friction carries a record of what the material experienced. The team also found that their foam's stiffness could be tuned in two directions: Squeezing it harder made it stiffer, while shaking it made it softer. The results could open a new direction for mechanical memory research beyond snap-through, two-state designs.
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