Irreversible behaviour of colloidal polycrystals following cyclic deformation

Colloidal suspensions are becoming a widely used tool to study the properties of matter, since the change of scale from the atomistic to the colloidal ones allows to directly observe phenomena that otherwise would not be within experimental reach. Colloidal suspensions, as well as disordered granular media, display an intriguing transition from reversible to irreversible deformation as the amplitude of the loading overcomes a threshold value. A team lead by Stefano Zapperi from CC&B with collaborators from Aalto University in Finland investigated the response of colloidal polycrystals to cyclic loading, by using molecular dynamics simulations. The simulations revealed a transition to irreversible behaviour driven by the displacement of dislocations. At the phase transition, the researchers observed enhanced particle diffusion, size-related effects and broadly distributed strain bursts. In addition to provide an analogy between the deformation of amorphous and polycrystalline materials, these results allow to reinterpret Zener pinning of grain boundaries as a way to prevent the onset of irreversible crystal ordering.

P. K. Jana, M. J. Alava and S. Zapperi,
Irreversible behaviour of colloidal polycrystals following cyclic deformation
Scientific Reports 7, Article number: 45550 (2017)
Available on: nature.com