Researchers have demonstrated for the first time that gold micro-particles have so-called shape memory and self-healing properties. This is a hugely interesting discovery and one that could lead to multiple advancements in technology and healthcare.
Shape memory means that a material has the ability to repair the damage caused to it and recover its original shape. Materials characterized by this ability, which has so far only been observed in very few metal alloys such as Nitinol, can exist in two stable crystalline forms, or phases: austenite and martensite. Austenite is the more symmetrical primary form stable at elevated temperatures and martensite is a phase characterized by lower symmetry but also by greater strength.
In more simple terms, molecules in the austenite phase are more symmetrically arranged and more rigid, whereas molecules in the martensite phase are more pliable (and therefore more resistant to strain) and less symmetrically arranged. The transition between these two phases happens, for example, in the quenching of steel.
The transformation from one phase to the next can be activated by applying mechanical load (e.g. weight) to the material or by cooling it down. With shape memory, a reverse phase transformation occurs from martensite back to its original austenite form when the material is heated up. The material “remembers” its original shape and is able to restore itself.
This is the first time that the shape memory phenomenon has been demonstrated in gold particles. The researchers made this discovery by indenting the gold particles with a sharp diamond tip controlled by an atomic force microscope (AFM). Annealing (the process of heating materials up and allowing them to cool slowly) of the particles to temperatures of about 65% of the absolute melting point of gold caused the particles to fully heal themselves of the damage and to recover to their original shape.
According to researchers, this discovery could lead to the design of mechanically stable and damage-tolerant components and devices at the sub-micrometer length scale.
For example, this means that longer-lasting mobile electronic devices (such as tablets and smartphones) could be developed, by preventing one of the main reasons for the failure of such devices, which is the mechanical wear of electrical contacts. Another possible application is the controlled drug delivery to the specific areas of a patient’s body.