Tuning the nature and position of yield point of a colloidal glass by an encoded memory

Maitri Mandal, Abhishek Ghadai and Sayantan Majumdar*

  *: speaker

Raman Research Institute, Bangalore 560080

Understanding yielding and plasticity of materials is important from both fundamental as well as engineering perspectives. For disordered materials such problem gets particularly challenging due to lack of correlation between the microscopic material failure and local structure. Here we experimentally study the shear induced yielding behaviour of a colloidal glass of PNIPAM particles where we observe a ductile-like yielding behaviour. Interestingly, when the system is trained/annealed sufficiently with cyclic shear, the yielding become brittle-like. Remarkably, the onset of such brittleness is correlated with the amplitude of the cyclic shear (\gamma_T) in a one to one manner. Such ductile to brittle transition persists for a significant range of \gamma_T; however, the strength of brittleness becomes maximum at an intermediate strain amplitude. In-situ boundary imaging of the sample seeded with tracer particles reveals that the onset of brittle yielding is correlated with the appearance of a shear band, whereas, in case of ductile yielding obtained for an untrained sample, the non-affinity appears all over the sample.