RFOT theory explains fragile-to-strong crossover in Wigner glasses

Colloidal suspension with various degrees of softness exhibits rich glass forming behavior, normally observed in molecular glasses. For over a decade, many experiments have shown that glass transition of colloidal suspensions can be either strong or fragile depending on the softness of potential, thus making them ideal testing ground for the structural glass transition (SGT) theories. However, it is still debated whether the softness alone is responsible for such a drastic change in fragility and if the glass transition of the soft colloid with the broad range of fragility can be described using a unified theory. We carried out Brownian dynamics simulations for a binary mixture of micron-sized charged colloidal suspensions and elucidate that they exhibit continuous transition from fragile to strong behavior due to the variation of the softness of potential that is achievable by changing the monovalent salt concentration. We found that the prediction of the random first order transition (RFOT) theory quantitatively describes the universal feature of the glass transitions of the charged colloids, such as growing length scales associated with heterogeneous dynamics. Our predictions are amenable to experimental tests.