Flow in binary colloidal glasses

Macroscopic strain exerted on materials with ideal crystallinity could be attributed to deformation of the most basic structural building block, namely the unit cell. In the case of glassy materials, the absence of long-range periodic order makes this correlation obsolete. Instead, external forces cause development of microscopic strain heterogeneities known as shear transformation zones (STZs). An important task in the physics of glasses is a comprehensive understanding of the role of STZs on the mechanics of the material. Tracing such structural rearrangements is experimentally challenging for the case of atomic or molecular glasses due to irrelevance of diffraction methods and also the need for using in-situ electron microscopy within the short-lived time scale of the deformation. In order to tackle such difficulties associated with small scale observations, larger model systems like colloidal glasses are selected such that they would be visible under fluorescence confocal microscope. The early goal of the project is to synthesize a binary colloidal system relevant for modelling a binary alloy. Afterwards, the objective will be focused on understanding the evolution of STZs in terms of their population, size, strain and activation energy along with their correlation to the short-range order. Relevance of Eshelby-type inclusion analysis for the STZs of the binary glass will be evaluated. Comparison of the results with those of a monodisperse system will be carried out with the aim of understanding the governing principles involved in atomic scale structural rearrangements of glasses.

Figure 1. Cartoon representation of a binary glassy system before and after exposure to external shear. Strain heterogeneities known as STZs (shown in the red ellipse) can evolve upon exertion of external force. Image adopted from M. L. Falk, J. S. Langer, Phys. Rev. E., 1998, 57, 7192–7207.