Growing dynamical facilitation on approaching the random pinning colloidal glass transition
-Shreyas Gokhale, K. Hima Nagamanasa, Rajesh Ganapathy and A. K. Sood
Nature Communications, 5, 4685, 2014.
Understanding the transformation of flowing liquids into rigid glasses remains one of the greatest challenges in contemporary condensed matter physics. Despite several decades of research, there is no consensus on whether the ubiquitous process of glass formation is fundamentally thermodynamic or dynamic in origin. Traditionally, the thermodynamic paradigm of the random First-order Transition theory (RFOT) has dominated theoretical research on the glass transition. Moreover, recent numerical simulations on glass transitions induced by randomly freezing a subset of particles in the liquid phase appear to lend further credence to it. Nonetheless, the purely kinetic perspective of the dynamical facilitation (DF) theory has emerged as a strong competing framework in the last few years. The primary reason for the persistence of this conundrum is the lack of direct experimental evidence that can distinguish between competing theories and thereby unravel the true nature of the glass transition. Here, using video microscopy, we show that dynamical facilitation in a colloidal glass-forming liquid exhibits unambiguous growth on approaching the glass transition. Further, by using holographic optical tweezers to simultaneously freeze several particles in the colloidal liquid, we show that dynamical facilitation plays a significant role in governing structural relaxation, even when the glass transition is induced by random pinning. In addition, we observe that heterogeneous dynamics in the form of string-like cooperative motion, which is believed to be consistent with RFOT, also emerges naturally within the framework of facilitation. Collectively, these findings suggest that a merger of existing theoretical approaches is imperative in order to gain a deeper understanding of the glass transition.