4TH INTERNATIONAL SYMPOSIUM ON SLOW DYNAMICS IN COMPLEX SYSTEMS: Keep Going Tohoku

Preface: 4th International Symposium on Slow Dynamics in Complex Systems
View Description Hide Description
 I. SUPER COOLED LIQUIDS AND GLASS TRANSITION


Glass transitions and critical points in orientationally disordered crystals and structural glassformers: ("Strong" liquids are more interesting than we thought)
View Description Hide DescriptionWhen liquids are classified using T_{g}scaled Arrhenius plots of relaxation times (or relative rates of entropy increase above T_{g}) across a "strongfragile" spectrum of behaviors, the "strong" liquids have always appeared rather uninteresting. Here we use updated plots of the same type for crystal phases of the "rotator" variety to confirm that the same pattern of behavior exists for these simpler (center of mass ordered) systems. However, in this case we can show that the "strong" systems owe their behavior to the existence of lambdatype orderdisorder transitions at higher temperatures (directly observable in the cases where observations are not interrupted by prior melting). Furthermore, the same observation can be made for other systems in which the glass transition, at which the ordering is arrested, occurs in the thermodynamic ground state of the system. This prompts an enquiry into the behavior of strong liquids at high temperatures. Using the case of silica itself, we again find strong evidence from extended ion dynamics simulations, for a lambda transition at high temperatures, but only if pressure is adjusted to a critical value. In this case the lambda point is identifiable as a liquidliquid critical point of the type suggested for supercooled water. We recognize the possibility of exploring, a postiori, the consequences of rapid cooling of laboratory liquid from >5000K and multiGPa pressures, using the phenomenology of damageinduced plasmas in optical fibers. The ramifications of these considerations will be explored to establish a "big picture" of the relation of thermodynamic transitions to supercooled liquid phenomenology.

Universal relaxation and diffusion in interacting complex systems: Fundamental physics and rich applications
View Description Hide DescriptionThe purpose of this paper is to make the research communities aware of the universality of the dynamic properties of manybody relaxation/diffusion processes of different kinds manifested in experiments and simulations on condensed matter with diverse chemical compositions and physical structures. I shall demonstrate the universality first from the dynamic processes in glassforming systems. This is reinforced by strikingly similar properties of different processes in contrasting interacting systems all having nothing to do with glass transition. The examples given here include glassforming systems of diverse chemical composition and physical structures, conductivity relaxation of ionic conductors (liquid, glassy and crystalline), translation and orientation ordered phase of rigid molecule, and polymer chain dynamics. Universality is found in the change of dynamics when dimension is reduced to nanometer size in widely different systems. Many more examples are given in Relaxation and Diffusion in Complex Systems , Springer, New York, (2011). The remarkable universality indicates that manybody relaxation/diffusion is governed by fundamental physics to be unveiled. One candidate is classical chaos in the theoretical basis of the Coupling Model, the predictions of which are in accord with the universal properties.

Irreversible equilibration and aging in glassforming liquids
View Description Hide DescriptionWe review the recentlyproposed nonequilibrium selfconsistent generalized Langevin equation (NESCGLE) theory of irreversible processes in liquids, and describe the scenario that emerges from its application to the equilibration (or absence of equilibration!) of quenched glassforming liquids. This theory extends to nonequilibrium conditions the SCGLE theory of dynamic arrest, which (just like the wellknown mode coupling theory) determines the boundary of the ergodic domain of the system. In this first systematic application of the nonequilibrium theory we consider a model softsphere glassforming liquid, initially at an ergodic equilibrium state, suddenly quenched to a lower final temperature that lies either (a) also in the ergodic domain, or (b) in the region of dynamically arrested states. In the first case the liquid will equilibrate within a finite equilibration time t^{eq} , while in the second the theory predicts that the liquid will age forever, (i.e., t^{eq} = ∞). The dynamic arrest boundary is thus predicted to determine the crossover from equilibration to aging, and to be characterized by the divergence of the equilibration time. In either case the theory predicts the irreversible tevolution of the measured static structure factor S(k;t) and of the dynamic properties such as the selfintermediate scattering function F_{S} (k, τ;t).

Relaxation processes in disaccharide sugar glasses
View Description Hide DescriptionWe represented relaxation processes of disaccharide sugars (anhydrous trehalose and maltose) in supercooled and glassy states by using several spectroscopy techniques which include a broadband dielectric loss spectroscopy, photon correlation spectroscopy and Xray diffraction (Retvield analysis) methods which are powerful tools to measure the dynamics in glass forming materials. In a dielectric loss spectroscopy study, we found that anhydrous trehalose and maltose glasses have an extra relaxation process besides α, JG β and γrelaxations which could be related to a unique property of glycoside bond in disaccharides. In photon correlation spectroscopy study, we found an interesting compressed exponential relaxation at temperatures above 140°C. The q ^{−1} dependence of its relaxation time corresponds to an ultraslow ballistic motion due to the local structure rearrangements. In the same temperature range, we found the glycosidic bond structure changes in trehalose molecule from the Raman and the Retvield Xray diffraction measurements indicating that the observed compressed exponential relaxation in supercooled liquid trehalose could be resulted in the glycosidic bond structure change. Therefore, the overall results from this study might support the fact that the superior bioprotection ability of disaccharide sugar glasses might originate from this unique relaxation process of glycosidic bond.

Control parameter dependence of transport coefficients near the glass transition
View Description Hide DescriptionThe master curves for transport coefficients, such as selfdiffusion coefficient D, shear viscosity η, and electrical conductivity σ, near the glass transition are studied based on the fact recently proposed by the present author that the longtime selfdiffusion coefficients in both fragile and strong liquids are well described by the following two types of master curves, depending on whether the control parameter is an intensive one (X) or an extensive one (Y); and , where and , X_{f} and Y_{f} being fictive singular points to be determined. Here ε = 4/3 for fragile liquids and 5/3 for strong liquids. The thermodynamic function Y = h(X) is then used to relate f(x) with g(y) and vice versa. The experimental data and the simulation results for the shear viscosity and the electrical conductivity are also analyzed by using the master curves f(x) and g(y). Thus, it is shown that any transport coefficients are well described by those master curves up to the deviation point, above which all the data start to deviate from the master curves and the system becomes out of equilibrium.

Dynamic heterogeneity in the glasslike monoclinic phases of some halogen methane compounds
View Description Hide DescriptionIn this work we study the heterogeneity of the dynamics on the lowtemperature monoclinic phases of the simple molecular glassy systems , n = 0, 1, 2. In these systems the disorder comes exclusively from reorientational jumps mainly around the C3 molecular axes. The different time scales are determined by means of the analysis of the spinlattice relaxation time obtained through Nuclear Quadrupole Resonance (NQR) technique. Results are compared with those obtained from dielectric spectroscopy, from which two α and βrelaxation times appear. NQR results enable us to ascribe with no doubt that the existence of two relaxations is due to dynamical heterogeneities which are the consequence of the different molecular surroundings of the molecules in the asymmetric unit cell of systems here studied.

The fragile to strong dynamical crossover in supercooled liquids. The oterphenyl case and its ergodicity at the dynamical arrest
View Description Hide DescriptionWe report a study of the dynamic crossover in two different glassforming materials: an adhesive hardsphere (AHS) colloidal system and the molecular liquid oterphenyl. Systems that present a fragiletostrong dynamical crossover in their transport parameters. A combination of light scattering, viscosity and nuclear magnetic resonance (NMR) is used to study the dynamical arrest in these systems. In both systems the data analysis is made in the conceptual framework of the Mode Coupling Theory in its extended version. For the AHS colloid, which is characterized by clustering process, we give evidence that the evolution toward the arrested phase can be described by using both the temperature and the concentration as the order parameter. The light scattering studies conducted on the oterphenyl confirm the suggestion of recent statistical mechanical approaches that such a molecular system remains ergodic also below the calorimetric glasstransition temperature.

Search for the firstorder liquidtoliquid phase transition in lowtemperature confined water by neutron scattering
View Description Hide DescriptionIt has been conjectured that a 1st order liquidtoliquid (LL) phase transition (LLPT) between high density liquid (HDL) and low density liquid (LDL) in supercooled water may exist, as a thermodynamic extension to the liquid phase of the 1st order transition established between the two bulk solid phases of amorphous ice, the high density amorphous ice (HDA) and the low density amorphous ice (LDA). In this paper, we first recall our previous attempts to establish the existence of the 1st order LL phase transition through the use of two neutron scattering techniques: a constant Q elastic diffraction study of isobaric temperature scan of the density, namely, the equation of state (EOS) measurements. A pronounced density hysteresis phenomenon in the temperature scan of the density above P = 1500 bar is observed which gives a plausible evidence of crossing the 1st order LL phase transition line above this pressure; an incoherent quasielastic scattering measurements of temperaturedependence of the αrelaxation time of at a series of pressures, namely, the study of the FragiletoStrong dynamic crossover (FSC) phenomenon as a function of pressure which we interpreted as the results of crossing the Widom line in the onephase region. In this new experiment, we used incoherent inelastic neutron scattering (INS) to measure the density of states (DOS) of H atoms in molecules in confined water as function of temperature and pressure, through which we may be able to follow the emergence of the LDL and HDL phases at supercooled temperature and high pressures. We here report for the first time the differences of librational and translational DOSs between the hypothetical HDL and LDL phases, which are similar to the corresponding differences between the wellestablished HDA and LDA ices. This is plausible evidence that the HDL and LDL phases are the thermodynamic extensions of the corresponding amorphous solid water HDA and LDA ices.

Nonlinear response of softsphere glasses to external fields
View Description Hide DescriptionNonlinear active microrheology in a glassforming softsphere mixture is studied using molecular dynamics computer simulation. To this end, a single tracer particle is pulled through the system by applying a constant force of magnitude f. After the tracer particle has reached a steady state moving with a constant velocity ν, the incoherent intermediate scattering function F _{s}(q, t) of the tracer is determined and analyzed for the directions parallel and perpendicular to the force with respect to its dependence on wavenumber q, time t, temperature T, and force strength f (note that due to the drift motion of the tracer particle, F _{s}(q, t) in parallel direction is a complex quantity). We find pronounced anisotropies in F _{s}(q,t) at low values of q; here, in parallel direction both the real and imaginary part of the incoherent intermediate scattering function, ReF _{s}(q,t) and ImF _{s}(q, t), may show an oscillatory behavior and ReF _{s}(q,t) in perpendicular direction decays much more slowly than the corresponding function in parallel direction. Approaching values of q that correspond to microscopic scales the anisotropies in ReF _{s}(q, t) vanish. In the latter regime, the decay of ReF _{s}(q, t) is similar to that of a tagged particle in the quiescent equilibrium state.

Slow dynamics in external forces: Creep and microrheology
View Description Hide DescriptionThe slow dynamics of dense liquids close to a glass transition is strongly influenced by external fields. We discuss the nonlinear response of glassforming model colloidal suspensions to external forces, applied either globally as an imposed shear stress (“creep” experiment), or locally as a singleparticle driving force (“microrheology” setup).

Cooperativity and heterogeneity in dynamics of glassforming systems
View Description Hide DescriptionThe role of dynamic cooperativity and heterogeneity in structural relaxation remains a great puzzle. We present estimates of the dynamic heterogeneity length scale ξ in many glass forming systems obtained using 4D NMR, derivative analysis of twopoints correlation function and the boson peak vibrations. Our analysis shows that ξ does not correlate to fragility of the system, while it correlates well to the sensitivity of structural relaxation to density. As the next step we discuss a relationship between dynamic heterogeneity and decoupling of diffusion from structural relaxation. We emphasize the problem of this approach in explaining recent data on decoupling phenomena. In the conclusion we suggest a general scenario for the dynamic heterogeneity and their role in structural relaxation.

The energy landscape of supercooled liquids: A tool to understand linear and nonlinear response
View Description Hide DescriptionWe study the dynamics of glassforming systems in terms of the statistics of their waiting times. For small glassforming systems their distributions can be obtained from the analysis of the potential energy landscape. The waiting times refer to the times between metabasin transitions. Whereas the dynamics of small systems is very well understood in terms of the potential energy landscape we consider two ways to complicate the dynamics. First, we study the impact of external forces on a single tagged particle. This corresponds to the microrheological case. We study the resulting mean square displacement in the moving coordinate frame. Depending on the underlying waiting time distribution one may observe superdiffusive, diffusive, or subdiffusive behavior for intermediate times. The shorttime and longtime limit can be calculated analytically. Beyond this interesting nonstandard behavior one also observes nonlinear response at large forces as reflected by a reduction of the average waiting time. More generally, the waiting time distribution experiences a systematic shift to shorter times. Furthermore, we relate the realspace trajectory to the actual transitions between metabasins and inherent structures of the potential energy landscape. Second, we discuss the effect of increasing the system size. Again, one observes a significant variation of the waiting time distribution. This effect can be rationalized in terms of the Coupled Landscape Model (CLM). In contrast to the application of an external force the effect of increasing the system size keeps, however, the first moment of the waiting time distribution constant.

Role of prepeaks in glassforming liquids
View Description Hide DescriptionMicrostructural and dynamical properties resulting from the hydrogen bonding interactions between ibuprofen molecules in the liquid state have been investigated by means of molecular dynamics computer simulations. Individual and collective dipole autocorrelation functions were calculated. They reveal that the behavior of the long time collective dipole correlation is dominated by the individual function due to antiparallel dipoles correlations in agreement with a value of the Kirkwood correlation factor significantly smaller than unity. The exact numeration of hydrogenbonding associating structures, their shapes cyclic or linear is a question that we have considered here. The existence of very stable small aggregates such as cyclic dimers and trimers is shown. The presence of these stable cyclic associating structures within homogeneous disordered phase are demonstrated to have a striking influence on the dynamical properties and might be at the origin of the unconventional Debye type process detected in this system. A comparison is made with the Debyetype relaxation found in microstructured monohydroxy alcohols.

Jamming and glass transitions viewed from the mean field pictures
View Description Hide DescriptionWe present several theoretical and numerical results which bolster the meanfield scenario of the glass and jamming transitions. The results of the replica theory, the modecoupling theory, and the simulation results are compared for the hard spheres in high dimensions, the ultrasoft potential fluids, and the jammed systems.

Nonlinear rheological response of colloidal glass
View Description Hide DescriptionI review a first principles approach to the nonlinear rheology of dense colloidal dispersions. Assuming homogeneous flow and neglecting hydrodynamic interactions, a theoretical description of the stresses, microstructure, and particle motion close to a colloidal glass transition are developed. Results for large amplitude oscillatory shearing, stepstrains, and other timedependent transient deformation protocols provide a unifying description of the dispersion properties under general strains including nonstationary situations. Shearthinning, plastic deformation and anelastic behaviour are observed. Adding Brownian dynamics simulations, the shearinduced particle motion provides information on the microscopic transport mechanisms in the dense dispersions.

Spontaneous bond orientational ordering in liquids: An intimate link between glass transition and crystallization
View Description Hide DescriptionThe origin of slow dynamics near glass transition and the mechanism of crystal nucleation are two unsolved fundamental problems associated with the metastable supercooled state of a liquid. So far these phenomena have been considered rather independently, however, we have revealed an intimate link between them. Recently we found that crystallike bond orientational order develops in the supercooled state of (nearly) singlecomponent systems such as spin liquids and weakly polydisperse colloidal liquids. In these liquids, low freeenergy configurations in a supercooled liquid have a link to the rotational symmetry which is going to be broken upon crystallization. We argue that this is a direct consequence of that the same free energy governs both glass transition and crystallization at least in this type of liquids. We found that it is such structural ordering at least in this type of liquids that causes glassy slow dynamics and dynamic heterogeneity. Furthermore, we revealed that such structural order also plays a crucial role in crystal nucleation: Crystallization is a process of the enhancement of spatial coherence of crystallike bond orientational order and ‘not’ driven by translational order at least in the nucleation stage. These results clearly indicate that the theoretical description at the twobody level is not enough to describe these phenomena and it is crucial to take into account many body correlations, particularly, bond orientational correlations. We argue that there is an intrinsic link between glass transition and crystallization if crystallization does not accompany other processes such as phase separation. If crystallization involves phase separation, on the other hand, such a direct link may be lost. We speculate that even in such a case glassy structural order may still be associated with low freeenergy local configurations.

Glass transitions in monolayers of colloidal ellipsoids
View Description Hide DescriptionGlass formers constitute of anisotropic particles was mainly studied by simulations in three dimensions with incomplete phase diagrams. Here we studied the structures and the glassy dynamics for translational and rotational motions in quasitwo dimensional (2D) suspensions of colloidal ellipsoids at the singleparticle level. At high densities, ellipsoids with large aspect ratio formed psuedonematic domains. Video microscopy revealed a twostep glass transition: rotational motion first becomes glassy due to the interdomain freezing, then translational motion become glassy at a higher density due to innerdomain freezing. Between the two transitions, ellipsoids formed an “orientational glass”. Below and near the respective glass transition densities, the rotational and translational fastestmoving particles moved cooperatively and formed clusters with powerlaw size distributions. The mean cluster sizes diverge in power law as approaching the glass transitions. The fast translational particles concentrated in pseudonematic domains and form bandlike clusters while the fast rotational particles mainly located around domain boundaries and form branchlike clusters.

Shear banding instabilities in amorphous solids: Predicting the yield strain
View Description Hide DescriptionWe present a short review of the theory of shear localization which results in shear bands in amorphous solids. As this is the main mechanism for the failure of metallic glasses, understanding the instability is invaluable in finding how to stabilize such materials against the tendency to shear localize. We explain the mechanism for shear localization under external shearstrain, which in 2dimensions is the appearance of highly correlated lines of Eshelbylike quadrupolar singularities which organize the nonaffine plastic flow of the amorphous solid into a shear band. We prove analytically that such highly correlated solutions in which N equidistant quadrupoles are aligned with equal orientations are minimum energy states when the strain is high enough. The line lies at 45 degrees to the compressive stress. We use the theory to first predict the yield strain at zero temperature and quasistatic conditions, but later generalize to the case of finite temperature and finite shear rates, deriving the JohnsonSamwer T ^{2/3} law.
