Dynamic Properties Of Supercooled Liquids Research Articles

Computer simulations and mode-coupling theory of glass-forming confined hard-sphere fluids.

We present mode-coupling theory (MCT) results for densely packed hard-sphere fluids confined between two parallel walls and compare them quantitatively to computer simulations. The numerical solution of MCT is calculated using the full system of matrix-valued integro-differential equations. We investigate several dynamical properties of supercooled liquids including scattering functions, frequency-dependent susceptibilities, and mean-square displacements. Close to the glass transition, we find quantitative agreement between the coherent scattering function predicted from theory and that evaluated from simulations, which enables us to make quantitative statements on caging and relaxation dynamics of the confined hard-sphere fluid.

New Insight Into Ion Transport Through Dynamic Modulus Studies

The dynamic properties of classical imidazolium ionic liquid [C8MIM][NTf2] are examined in terms of the new physical quantity “modulus of elasticity” (M), being defined as the ratio of activation energy (Eact) and activation volume (Vact), parameters determined from isobaric and isothermal dc-conductivity data, respectively. By taking advantage of the T-V version of Avramov entropic model we demonstrate that the dynamic modulus can be defined by means of thermodynamic quantities, i.e. isothermal compressibility and thermal expansion coefficient. From this point of view a new connection between thermodynamic and dynamic properties of supercooled liquids, being an alternative to the density scaling idea, is provided.

Dynamic heterogeneity in crossover spin facilitated model of supercooled liquid and fractional Stokes-Einstein relation.

Kinetically constrained models have gained much interest as models that assign the origins of interesting dynamic properties of supercooled liquids to dynamical facilitation mechanisms that have been revealed in many experiments and numerical simulations. In this work, we investigate the dynamic heterogeneity in the fragile-to-strong liquid via Monte Carlo method using the model that linearly interpolates between the strong liquid-like behavior and the fragile liquid-like behavior by an asymmetry parameter b. When the asymmetry parameter is sufficiently small, smooth fragile-to-strong transition is observed both in the relaxation time and the diffusion constant. Using these physical quantities, we investigate fractional Stokes-Einstein relations observed in this model. When b is fixed, the system shows constant power law exponent under the temperature change, and the exponent has the value between that of the Frederickson-Andersen model and the East model. Furthermore, we investigate the dynamic length scale of our systems and also find the crossover relation between the relaxation time. We ascribe the competition between energetically favored symmetric relaxation mechanism and entropically favored asymmetric relaxation mechanism to the fragile-to-strong crossover behavior.

On the pressure evolution of dynamic properties of supercooled liquids

A pressure counterpart of the Vogel–Fulcher–Tammann (VFT) equation for representingthe evolution of dielectric relaxation times or related dynamic properties is discussed:τ(P) = τ0Pexp[DPΔP(P0−ΔP)], whereΔP = P−PSL,P0 is the ideal glasspressure estimation, DP is the pressure fragility strength coefficient, and the prefactorτ0P is related to the relaxation time at the stability limit(PSL)in the negative pressure domain. The discussion is extended to the Avramov model (AvM) relationτ(T,P) = τ0exp[ε(Tg(P)/T)D],supplemented with a modified Simon–Glatzel-type equation for the pressure dependence of the glasstemperature (Tg(P)), enabling an insight into the negative pressure region. A recently postulated (Dyre 2006Rev. Mod. Phys. 78 953) comparison between the VFT and the AvM-type descriptions isexamined, for both the temperature and the pressure paths. Finally, we address thequestion ‘Does fragility depend on pressure?’ from the title of Paluch M et al (2001J. Chem. Phys. 114 8048) and propose a pressure counterpart for the ‘Angellplot’.

Transitions between inherent structures in water

The energy landscape approach has been useful to help understand the dynamic properties of supercooled liquids and the connection between these properties and thermodynamics. The analysis in numerical models of the inherent structure (IS) trajectories-the set of local minima visited by the liquid-offers the possibility of filtering out the vibrational component of the motion of the system on the potential energy surface and thereby resolving the slow structural component more efficiently. Here we report an analysis of an IS trajectory for a widely studied water model, focusing on the changes in hydrogen bond connectivity that give rise to many IS's separated by relatively small energy barriers. We find that while the system travels through these IS's, the structure of the bond network is continuously modified, exchanging linear bonds for bifurcated bonds and usually reversing the exchange to return to nearly the same initial configuration. For the 216-molecule system we investigate, the time scale of these transitions is as small as the simulation time scale ( approximately 1 fs). Hence, for water, the transition between each of these IS's is relatively small and eventual relaxation of the system occurs only by many of these transitions. We find that during IS changes the molecules with the greatest displacements move in small "clusters" of 1-10 molecules with displacements of approximately 0.02-0.2 nm, not unlike simpler liquids. However, for water these clusters appear to be somewhat more branched than the linear "stringlike" clusters formed in a supercooled Lennard-Jones system found by Glotzer and her collaborators.

Structural heterogeneity in supercooled liquids and glasses

Molecular-dynamics (MD) simulation has been used to study the dynamical properties of supercooled liquids near the glass transition temperature. We have found the dynamical heterogeneity for microscopic and semi-macroscopic time scales. Careful analyses with a large-size molecular dynamics simulation have been made to demonstrate well-defined correlations among motions of atoms in time windows corresponding to α and β relaxations. These correlated motions of atoms of particular interest may lead to the spatial–temporal heterogeneity which are attributed to particular dynamical origins. These heterogeneities originate from linearly correlated jump motions up to about the order of ten atoms which occurs in semi-macroscopic time scale and linearly correlated motions of atoms composed of the order of more than hundred atoms which lasts only for microscopic time scale. These two correlated motions are connected in supercooled liquids and glasses.

Structure Relaxation in Super-Cooled Liquids

Dynamical properties of super-cooled liquids are studied in the intermediate wavenumber region. A polarization function is shown to describe the relaxation of the structure sustaining effective potentials. Effects of its slow relaxation are discussed on the dynamical structure factor as well as the transverse current correlation function for liquid argon.

Studies in Fluid Mechanics and Applied Mathematics. Edited by H. H ASIMOTO and T. T ATSUMI . 1975 Elementary Fluid Mechanics, 5th edition. By J. K. V ENNARD and R. L. S TREET . Wiley, 1975. 740pp. £9.50 or $17.95 The Dynamic Properties of Supercooled Liquids. By G. H ARRISON . Academic Press, 1976. 199 pp. £6.20 IUTAM Symposium Transsonicum

Studies in Fluid Mechanics and Applied Mathematics. Edited by H. HASIMOTO and T. TATSUMI. 1975 Elementary Fluid Mechanics, 5th edition. By J. K. VENNARD and R. L. STREET. Wiley, 1975. 740pp. £9.50 or 29.50. Liquid Thermal Conductivity. A Data Survey to 1973. By E. T. JAMIESON, J. B. IRVING and J. S. TUDHOPE. Her Majesty's Stationary Office, 1975. 221 pp. £9.40. Viscosity. By Y. S. TOULOKIAN, S. C. SAXENA and P. HESTERMANS. Plenum, 1975. 643 pp. - Volume 78 Issue 4