The fragile-to-strong dynamical crossover and the system viscoelasticity in attractive glass forming colloids

Abstract

The dynamical arrest phenomena of an adhesive hard-sphere (AHS) colloid, L64-D 2 O system has been studied by using calorimetry and the complex shear modulus. This system is characterized by a rich temperature

50th Anniversary Perspective: Challenges in the Dynamics and Kinetics of Glass-Forming Polymers

“…The VFT or WLF finite temperature divergence of the dynamics of glass-forming materials has been known, now, for almost 100 years, and until recently, theories of the glass transition have considered that the VFT/WLF behavior was a required signature of the glass-forming liquid. The super-Arrhenius temperature behavior is observed in a temperature range of approximately T g + 10 to T g + 100 K. ,, At the high end of temperatures, it is well understood that there is a tendency for the temperature dependence to asymptote toward an Arrhenius behavior with an activation energy typical of molecular flow or perhaps to a different high-temperature WLF response. − On the other hand, as one approaches and goes below the nominal T g , it has become controversial whether or not the equilibrium dynamic response continues on the super-Arrhenius line or falls off toward a weaker temperature dependence and, further, whether or not the weaker temperature dependence becomes Arrhenius-like such that the divergence of the dynamics or viscosity at a finite temperature is lost. ,,− A view of this can be had by considering Figure . , The plot is taken from polycarbonate data and shows multiple aspects of the problem. First, the WLF or VFT curve is the nominal equilibrium response according to the conventional wisdom and is valid above the glass transition temperature range.…”

“…The first evidence that there may be an issue of the super-Arrhenius temperature behavior not being followed as one gets near to or below the glass transition temperature perhaps comes from an early observation of Kovacs et al: “It is evident that the WLF equation cannot be applied in the immediate vicinity of T g with the same parameters that apply far above this temperature. Although the rule of thumb is often stated that the WLF equation holds from T g to T g + 100 °C, the lower limit probably should be raised to T g + 10 °C, while there is some evidence that the upper limit also can be raised.” The Stickel plot, a derivative analysis, further undermines the idea of a broad range of temperatures being described by a single VFT/WLF expression with even some evidence , in certain systems of Arrhenius behavior appearing at lower temperatures. In addition, early work coming from DiMarzio and Yang and more recent contributions from the group of Dyre , have provided some theoretical underpinnings to the idea that the assumed continuation of the VFT/WLF behavior may not be a correct extrapolation.…”

“…Although the rule of thumb is often stated 11 that the WLF equation holds from T g to T g + 100 °C, the lower limit probably should be raised to T g + 10 °C, while there is some evidence 204 that the upper limit also can be raised." The Stickel plot, 176 a derivative analysis, further undermines the idea of a broad range of temperatures being described by a single VFT/WLF expression with even some evidence 177,178 in certain systems of Arrhenius behavior appearing at lower temperatures. In addition, early work coming from DiMarzio and Yang 179 and more recent contributions from the group of Dyre 205,206 have provided some theoretical underpinnings to the idea that the assumed continuation of the VFT/WLF behavior may not be a correct extrapolation.…”

The Proton Density of States in Confined Water (H2O)

“…Firstly, it is due to the role of water in life sciences where it plays a fundamental role in the biological activity starting from the microscopic scales typical of proteins, the cells and membranes and their functions up to the macroscopic one of the living organs, thus involving directly many sciences from biology to chemistry and physics [21,37,38,39]. Secondly, confined water with porous media such as silica gel and zeolites is of special importance for technological applications [40]; other systems that impose spatial constraints to water molecules are polymers, polymer gels, clays, vesicles, microemulsions and micelles where the balance between hydrophilic and hydrophobic originates structural self-organization [25,41,42,43]. However, confined water is also of interest because it can be considered as a model for water inside the deep supercooled regime where bulk water cannot be studied [44].…”