Nanoscale Tetrapods Could Provide Early Warning of a Material’s Failure

These atom-scale computer simulations of tetrapods show how they sense compression (left) and tension along one axis (right), both of which are crucial to detecting nanoscale crack formation. The color bar indicates the percent change of the tetrapods' volume. (Credit: Berkeley Lab) Light-emitting, four-armed nanocrystals could someday form the basis of an early warning system in structural materials by revealing microscopic cracks that portend failure, thanks to recent research by scientists from the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley. The researchers embedded tetrapod-shaped quantum dots, which are nanosized semiconducting particles, in a polymer film. The tetrapods? cores emit fluorescent light when their arms are twisted or bent out of shape. This indicates the polymer is undergoing a degree of tensile or compressive strain, from which stress over sub-micron-scale regions of the material can be detected. Such stress can cause nanoscale cracks to develop into macroscopic failure. Initial tests show the tetrapods can cycle more than 20 times without losing their ability to sense stress, and they don't degrade the strength of the polymer in which they're matrixed.