Liquid Fragility and the Glass Transition in Water and Aqueous Solutions (original) (raw)
Related papers
Journal of Non-Crystalline Solids, 2006
Here we compile literature data for dynamic fragility m for six types of glass forming liquids: polymers, small molecule organics, hydrogen bonding organics, inorganics, ionic and metallic glass formers. Our analysis of the data shows that different categories of glass forming liquids exhibit different behaviors in terms of the correlation between m and T g , a correlation not previously examined. For example, for hydrogen bonding organics, polymeric and metallic glass formers, there is an approximately linear increase in m with increasing T g. While for inorganic glass formers, m appears almost independent of T g , remaining nearly constant over a wide range in T g. At the same time, another important parameter, the apparent activation energy E g at T g has been investigated. It was found that E g increases with T g to the 2nd power for hydrogen bonding organics, polymeric and metallic glass forming liquids, while E g of inorganic glasses has a linear dependence on T g .
Journal of Physics: Condensed Matter, 2010
A low temperature Monte Carlo dynamics of a Keating like oscillator model is used to study the relationship between the nature of glasses from the viewpoint of rigidity, and the strong-fragile behaviour of glass-forming liquids. The model shows that a Phillips optimal glass formation with minimal enthalpic changes is obtained under a cooling/annealing cycle when the system is optimally constrained by the harmonic interactions, i.e. when it is isostatically rigid. For these peculiar systems, the computed fragility shows also a minimum, which demonstrates that isostatically rigid glasses are strong (Arrhenius-like) glass-forming liquids. Experiments on chalcogenide and oxide glass-forming liquids are discussed under this new perspective and confirm the theoretical prediction for chalcogenide network glasses. PACS numbers: 61.43.Fs-61.20.-x
Temperature Dependence of Structural Relaxation in Glass-Forming Liquids and Polymers
Entropy
Understanding the microscopic mechanism of the transition of glass remains one of the most challenging topics in Condensed Matter Physics. What controls the sharp slowing down of molecular motion upon approaching the glass transition temperature Tg, whether there is an underlying thermodynamic transition at some finite temperature below Tg, what the role of cooperativity and heterogeneity are, and many other questions continue to be topics of active discussions. This review focuses on the mechanisms that control the steepness of the temperature dependence of structural relaxation (fragility) in glass-forming liquids. We present a brief overview of the basic theoretical models and their experimental tests, analyzing their predictions for fragility and emphasizing the successes and failures of the models. Special attention is focused on the connection of fast dynamics on picosecond time scales to the behavior of structural relaxation on much longer time scales. A separate section disc...
Qualitative change in structural dynamics of some glass-forming systems
Physical Review E, 2015
Analysis of temperature dependence of structural relaxation time τ(T) in supercooled liquids revealed a qualitatively distinct feature-a sharp, cusp-like maximum in the second derivative of log τ α (T) at some T max. It suggests that the super-Arrhenius temperature dependence of τ α (T) in glass-forming liquids eventually crosses over to an Arrhenius behavior at T<T max , and there is no divergence of τ α (T) at non-zero T. T max can be above or below T g , depending on sensitivity of τ(T) to change in liquid's density quantified by the exponent γ in the scaling τ α (T) ~ exp(A/Tρ-γ). These results might turn the discussion of the glass transition to the new avenue-the origin of the limiting activation energy for structural relaxation at low T.
The glass transition is described as a time-and history-independent singular event, which takes place in an interval dependent on the distribution width of the molecular vibration amplitudes. Free volume is redefined and its generation is the result of the fluctuating transfer of thermal energy into the condensed matter and the resulting combined interactions between the vibration elements. This creates vacancies between the elements which are larger than the cross-section of an adjacent element or parts thereof. Possible shifts of molecules or molecular parts through such gaps depend on the size and axis orientation and do not require further energetic activation. After a displacement additional volume is created by delays in occupying abandoned positions and restoring the energetic equilibrium. The different possibilities of axis orientation in space result in different diffusive behavior of simple molecules and chain molecules, silicate network formers and associating liquids. Glass transformation takes place at a critical volume Vg 0 when the cross-section of the apertures becomes smaller than the cross-section of the smallest molecular parts. The glass transition temperature Tg 0 is assigned to Vg 0 and is therefore independent of molecular relaxation processes. Tg 0 is well above the Kauzmann and Vogel temperatures, usually just a few degrees below the conventionally measured glass temperature Tg(qT). The specific volume at the two temperatures mentioned above cannot be achieved by a glass with an unordered structure but only with aligned molecular axes, i. e. in the crystalline state. Simple liquids consisting of non-spherical molecules additionally alter their behavior above Vg 0 at Vg l where the biggest gaps are as small as the largest molecular diameter. Tg l is located in the region of the crystalline melting point Tm. Both regions, above and below Tm, belong to different physical states and have to be treated separately. In the region close to Vg 0 resp. Tg 0 the distribution of vibration amplitudes has to be taken into account. The boundary volume Vg 0 and the creation of apertures larger than the cross-section of the vibrating elements or parts thereof, in conjunction with the distribution width of the molecular vibrations approaching Vg 0 and the molecular axis orientation, is the key to understanding the glass transition.
arXiv: Statistical Mechanics, 2020
The characterization of the non-Arrhenius behavior of glass-forming liquids is a broad avenue for research toward the understanding of the formation mechanisms of noncrystalline materials. In this context, this paper explores the main properties of the viscosity of glass-forming systems, considering super-Arrhenius diffusive processes. More precisely, we establish the viscous activation energy as a function of the temperature, in which we measure the fragility degree of the system and characterize the fragile-to-strong transition, through the standard Angell's plot in a two-state model. Our results show that the non-Arrhenius behavior observed in fragile liquids can be understood as a consequence of the non-Markovian dynamics that characterizes the diffusive processes of these systems, and the fragile-to-strong transition corresponds to the attenuation of long-range spatio-temporal correlations during the glass transition process.
On the correlation between fragility and stretching in glass-forming liquids
Journal of Physics: Condensed Matter, 2007
We study the pressure and temperature dependences of the dielectric relaxation of two molecular glass-forming liquids, dibutyl phthalate and m-toluidine. We focus on two characteristics of the slowing down of relaxation, the fragility associated with the temperature dependence and the stretching characterizing the relaxation function. We combine our data with data from the literature to revisit the proposed correlation between these two quantities. We do this in light of constraints that we suggest to put on the search for empirical correlations among properties of glass-formers. In particular, we argue that a meaningful correlation is to be looked for between stretching and isochoric fragility, as both seem to be constant under isochronic conditions and thereby reflect the intrinsic effect of temperature.
Physica A: Statistical Mechanics and its Applications, 2016
The systematic method to explore how the dynamics of strong liquids (S) is different from that of fragile liquids (F) near the glass transition is proposed from a unified point of view based on the mean-field theory discussed recently by Tokuyama. The extensive molecular-dynamics simulations are performed on different glass-forming materials. The simulation results for the mean-nth displacement M n (t) are then analyzed from the unified point of view, where n is an even number. Thus, it is first shown that in each type of liquids there exists a master curve H (i) n as M n (t) = R n H (i) n (v th t/R; D/Rv th) onto which any simulation results collapse at the same value of D/Rv th , where R is a characteristic length such as an interatomic distance, D a long-time selfdiffusion coefficient, v th a thermal velocity, and i =F and S. The master curves H (F) n and H (S) n are then shown not to coincide with each other in the so-called cage region even at the same value of D/Rv th. Thus, it is emphasized that the dynamics of strong liquids is quite different from that of fragile liquids. A new type of strong liquids recently proposed is also tested systematically from this unified point of view. The dynamics of a new type is then shown to be different from that of well-known network glass formers in the cage region, although both liquids are classified as a strong liquid. Thus, it is suggested that a smaller grouping is further needed in strong liquids, depending on whether they have a network or not.
Specific Heat and Ultrasonics as Dynamic Probes of the Glass Transitiona
Annals of the New York Academy of Sciences, 1986
Specific heat and sound propagation measurements are historically of particular importance to the study of the glass transition. Indeed, the glass transition can be viewed either as the change that occurs as a liquid begins to support a shear and thus becomes able to propagate transverse sound or as an anomaly in the specific heat, cp, of the supercooled liquid. The ability to support a shear is, after all, what distinguishes a solid from a liquid. On the other hand, the specific heat anomaly, where cp falls from a value appropriate to a liquid to a value close to that of a crystal as the temperature is lowered, is the basis of the Kauzmann paradox,' one of the clearest indications that some sort of transition must take place between the liquid and the glass. If there were no specific heat anomaly, then, since the specific heat of a supercooled liquid is larger than that of the crystal, the entropy of the liquid would eventually become much less than that of the crystal as the temperature is lowered. This, of course, has never been observed because the glass transition invariably intervenes before such a bizarre situation has the chance to arise.