Failure of spherical colloidal crystals

It is not possible to place a crystal on a sphere, as it is apparent by looking at a soccer ball. In that case, one has to introduce in the hexagonal crystals 12 extra pentagons, representing the topological defects of the crystal. Understanding the mechanical stability of spherical crystalline shells when they are deformed is of fundamental importance because these structures are at the forefront in the drive to fabricate new functionalized self-assembled materials.

In paper published in PNAS, CC&B scientists Carlotta Negri, Alessandro Sellerio and Stefano Zapperi show how topological defects help curved crystals to adapt their shape when the sphere is squeezed. The same defects, however, represent the weakest spot where fracture initiates when the sphere is inflated. The work, in collaboration with the University of Barcelona, is based on extensive numerical simulations of interacting colloidal particles confined to a surface. The results highlight the fundamental role played by geometrically necessary crystal defects in controlling mechanical stability and plastic rearrangements of the shell.

Carlotta Negri, Alessandro L. Sellerio, Stefano Zapperi, and M. Carmen Miguel
Deformation and failure of curved colloidal crystal shells
PNAS 2015 ; published ahead of print November 9, 2015, doi:10.1073/pnas.1518258112
Available on: www.pnas.org