Mode coupling theory and fragile to strong transition in supercooled TIP4P/2005 water

Abstract

We study by molecular dynamics simulations supercooled water with the TIP4P/2005 potential. This model is able to predict many properties of water in a large range of the thermodynamic space in agreement with experiments. We explore the dynamical behavior and, in particular, the self intermediate scattering function of the oxygen atoms. We find that the structural relaxation in the range of mild supercooling is in agreement with the Mode Coupling Theory (MCT). The ideal MCT crossover takes place at decreasing temperature with increasing density. Deviations from the MCT behavior are found upon further supercooling. A crossover from the MCT, fragile, regime to a strong, Arrhenius, regime is found and it is connected to the presence of a liquid-liquid phase transition and the Widom line emanating from the liquid-liquid critical point.

Pressure dependence of viscosity in supercooled water and a unified approach for thermodynamic and dynamic anomalies of water

“…Because f increases upon cooling, water dynamics switches from a fragile HDS-dominated regime at high temperature to a strong LDS-dominated regime at low temperature. The crossover occurs along the Widom line, where f reaches 1/2 and varies the most rapidly (37); this confirms the simulation results (29)(30)(31) and gives a quantitative explanation of the link between thermodynamics and dynamics. The VTF law that describes the fragile HDS has been justified based on the Adam-Gibbs theory (41) and T0 identified with the Kauzmann temperature at which the configurational entropy would vanish; hence T0 should lie below the glass transition temperature Tg for a theoretical system made of pure HDS.…”

“…Emanating from this point, in the one-phase supercritical region, the locus of maxima in correlation length associated with the transition defines the Widom line. Simulations find that the dynamic crossover precisely occurs along this Widom line (29)(30)(31), pointing toward a link between thermodynamics and dynamics.…”

“…Observation of this crossover has been reported for confined water, but this is still a debated topic (24). Simulation studies of bulk water with several potentials (25)(26)(27)(28)(29)(30)(31) find that structural relaxation for mild supercooling is well described by mode coupling theory (MCT), which predicts a fragile regime with a power-law dependence for the dynamic properties. Complete dynamic arrest is avoided by the emergence of hopping processes, which yield a crossover to strong, Arrhenius behavior at lower temperatures.…”

Slow Dynamics and Structure of Supercooled Water in Confinement

“…It is of particular interest that, in simulations, the fragile to strong crossover (FSC) was found to occur along the isobaric path in coincidence with the crossing of Widom line emanating from the LLCP [43,50,52]. Results of experiments on water in MCM-41 give support to this result [43,46].…”

Concentrated suspensions of Brownian beads in water: dynamic heterogeneities through a simple experimental technique

“…Different numerical models of amorphous solids and glass-formers have been recently proposed to capture this stretched-to-compressed exponential crossover [34][35][36][37], but its general understanding is still under debate. We notice that, in our case, the sharp increase of β at the largest volume fraction may signal a breakdown of the Mode Coupling regime and the onset of a different regime: it might be associated to the famous "fragile-to-strong" crossover observed in supercooled molecular liquids [38,39], especially water [40][41][42][43][44][45][46][47][48], and in colloidal glasses [49], also as a consequence of aging [50,51]. Association of strecthed-to-compressed and fragile-to-strong crossovers can also be inferred from recent experiments on microgel and metallic glasses [33].…”