Oral Presentation 26th ACMM “2020 Visions in Microscopy”

Connecting local structure and dynamics to shear-induced structural transformations in a colloidal glass using scanning micro-beam small angle x-ray scattering (#110)

Amelia CY Liu 1 , Espen Bøjesen 2 , Rico F Tabor 3 , Stephen T Mudie 4 , Peter Harrowell 5 , Alessio Zaccone 6 , Timothy C Petersen 2
  1. School of Physics and Astronomy, Monash University, Clayton, Victoria, Australia
  2. Monash Centre for Electron Microscopy, Monash University, Clayton, Victoria, Australia
  3. School of Chemistry, Monash University, Clayton, Victoria, Australia
  4. Australian Synchrotron, Clayton, Victoria, Australia
  5. School of Chemistry, University of Sydney, Sydney, New South Wales, Australia
  6. Department of Physics, University of Milan, Milan, Italy

Large area diffraction patterns of glasses are composed of diffuse, isotropic rings that arise from the large variety of local structures that exist in the disordered material. If the diffracting volume is limited to the correlation length, this isotropic diffracted intensity breaks up into discrete regions. The angular symmetry of such patterns reflects the local symmetries in the glass’ structure [1-4]. We measured the average angular symmetries from an ensemble of scanning microbeam small-angle x-ray scattering (SAXS) patterns from a colloidal glass and found that they were strong fingerprints of local order. The order could be tuned using different additives (either BCC, FCC, or ICOS) and corresponded to the stable phase in the underlying, lower density, equilibrium phase diagram [5]. In a further study of these glasses the local symmetries from scanning micro-SAXS were mapped and compared to the local time correlation coefficient obtained from successive spatial scans. This work demonstrated that low symmetry local structures were linked to larger amplitude dynamics. Examining the structural transformations after the application of compressive and shear stress it was found these same low-symmetry local structures were associated with shear instabilities where strain became localized in a shear “band”. The shear band involved co-operative transformations of local structures with a diameter 50-100 times the size of the particle, showing that understanding the behaviour of complex disordered structures requires connection between both local and global structure.

This research was undertaken in part using the SAXS/WAXS beamline at the Australian Synchrotron, part of ANSTO. ACYL acknowledges support from the ARC (FT180100594). EB acknowledges funding from the Villum Foundation and the Carlsberg Foundation.

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  5. A. C. Y. Liu, R. F. Tabor, M. D. de Jonge, S. T. Mudie, and T. C. Petersen, Proc. Nat. Academy Sci., 114, 10344–10349, (2017)