Research Highlights

Direct experimental evidence for thermodynamic origin of the glass transition

- A K Sood, Physics

The colossal increase in viscosity, without a concomitant onset of structural order, is a hallmark feature of the glass transition. This lack of accompanying order raises the fundamental question of whether the glass transition is thermodynamic or purely dynamic in origin. The Random First-Order Transition theory  (RFOT) suggests that glasses do in fact exhibit a subtle form of ‘amorphous’ structural order that is only manifested in static many body correlations, a conjecture supported by numerical simulations. In a recent work, which has appeared in Nature Physics ( April 2015, DOI: 10.1038/Nphy3289), we have provided the first experimental evidence of the growing amorphous order envisioned in RFOT by using holographic optical tweezers to pin an amorphous wall of particles in  a colloidal-glass-forming liquid. We have experimentally demonstrated unambiguously the non-monotonic evolution of dynamic correlations on approaching the glass transition and shown that this non-monotonicity is consistent with the change in morphology of cooperatively rearranging regions, as predicted by the RFOT. By reinforcing the thermodynamic paradigm of glass transition, our results constitute a pivotal step in distinguishing between competing theories of glass formation.  The authors of this work are K Hima Nagamanasa (graduate student at JNCASR ), Shreyas Gokhale (graduate student at IISc), Professor A.K. Sood (IISc) and Professor  Rajesh Ganapathy (JNCASR).