While traditional dynamic light scattering is useful for following structural relaxation in the liquid, in the glassy domain the technique is limited by the ultimate patience of the experimentalist; i.e., the structural relaxation can not be measured when the experimental time scale is less than the structural relaxation time. Nevertheless, we show how useful information regarding structural relaxation can be accessed from light scattering in the glass using a novel ensemble-averaged technique. Dynamic light scattering (DLS) measurements performed on glass forming orthoterphenyl show an inequality between time and ensemble average correlation functions near and below the calorimetrie glass transition temperature, Tg, and hence demonstrate ergodicity breaking. Our ensemble averaged measurements provide a measure of the so-called non-ergodicity parameter, fq, below Tg. Our DLS results for orthoterphenyl indicate that the functional form for fq is consistent with Mode Coupling theory predictions, but occurs at the glass transition temperature, Tg≈243K, rather than at TC≈290K as observed in neutron scattering studies.

An investigation was conducted of the effects of the advancement of chemical reactions and the prepolymer molecular weight on the reorientational dynamics and intermolecular cooperativity in reactive epoxy-amine systems. Experimental results were obtained by dielectric spectroscopy over a wide range of frequency (1 mHz to 1 GHz) and temperature (−170 to +200 °C). A strong effect of the progress of reaction on reorientational dynamics was noted and, for the first time, an explanation was put forward within the framework of the coupling theory. It was proposed that the molecular-level characteristics of a reactive system that affect its intermolecular cooperativity can be classified into two categories: 1) molecular architecture - determined by molecular symmetry, rigidity and steric hindrance; and 2) dielectric architecture - determined by the type and concentration of all dielectrically active species.

We discuss some aspects of the links between the behaviour and theory of spin glasses and that of structural glasses of the fragile type. We review the present status of the conjecture according to which a certain class of spin glass mean field theories (those with first order transitions) could provide a mean field theory for the glass transition. Recent developments pointing in that direction include the existence of spin glasses without disorder, and the general link between Mode-Coupling Theory (MCT) and the motion of a particle in a random potential. This link enables one to generalize the MCT equations for temperatures below the glass transition, and to describe aging effects. We compare these results with those obtained within more phonomonological ‘trap’ models.

A new model for molecular rearrangements in liquids is proposed. The liquids are regarded as dense ensembles of vibrating molecules satisfying the excluded volume condition. A continuity condition is applied on the molecular scale of such systems and is regarded as controlling rearrangements leading to translations of molecules beyond the range of their vibration amplitude. It results in cooperative rearrangements which are considered as taking place in systems with fluctuating density. Rates of rearrangements are considered as being controlled by thermal activation with activation energy barriers dependent on local density. Various dependencies of the activation energy barriers on local density are examined. It is shown, that the model is able to reproduce the extremal cases of temperature dependencies of relaxation times represented on one edge by the Arrhenius relation and on the other edge by the Vogel-Fulcher-Tamman relation. The model can, however, provide a broad spectrum of other dependencies filling the gap between these extremes. All cases are based on the uniform microscopic picture of cooperative molecular rearrangements resulting from system continuity. The model is implemented as a simulation algorithm (Dynamic Lattice Liquid - DLL algorithm) which is used to simulate dynamic properties of liquids and polymer melts. Simulation results obtained for polymers are compared with experimental results obtained by means of the dynamic mechanical measurements on polyisobutylene samples with various molecular weights.

The temperature dependence of the microstructure and local dynamics in the paramagnetic phase of the d = 2 and d = 3 ± J Ising spin glass model is examined by comparing the equilibrium distributions of local flip-rates and local energies calculated in large-scale Monte Carlo simulations. The emergence in this model of fast processes as the glass transition is approached corresponds with recent experimental results.

We have analyzed a non-randomly frustrated spin model which exhibits behavior remarkably similar to the phenomenology of structural glasses. The high-temperature disordered phase undergoes a strong first-order transition to a long-range ordered structure. Using Monte Carlo simulations, we have studied the behavior of the supercooled state by quenching to temperatures below this transition temperature. For a range of supercooling, the system remains ergodic and exhibits dynamics characteristic of supercooled liquids. Below a certain characteristic temperature, however, the system freezes into a “glassy” phase. In this phase, the system is non-ergodic and evolves through a distribution of traps characterized by a power-law distribution of trapping times. This change in the dynamic behavior is concurrent with the appearance of a shear instability.

We review some recent results on the self-dynamics in deep supercooled (simulated) water, obtained by analyzing very long Molecular Dynamics simulations. We discuss the possibility of interpreting the observed slowing down of the dynamics in terms of Mode Coupling Theory for supercooled liquids and, at the same time, of associating the experimentally observed anomalies of the transport coefficients in water on lowering the temperature to the formation of long living cages. The so-called critical Angeli temperature TA in supercooled water could be interpreted as kinetic glass transition temperature, relaxing the need of a thermodynamic singularity for the explanation of the dynamic anomalies of liquid water. In the end we discuss the possibility that TA acts as cross-over temperature from fragile to strong liquid behavior.

Simulation of soda-lime-silicate (sis) glass has been performed using molecular dynamics (MD). The local structure of each component is analyzed extensively in terms of total radial distribution function and coordination number and found to be insensitive to the composition change. Because of its big size, Na+/Ca2+ shows a behavior rather like O2− instead of Si4+. It is evident that the CN and local structure of Na+ with O2− are similar to those in crystalline a-Na2Si2O5. Finally, the Na+/Ca2+ cluster phenomenon is discussed.

It is shown that the coupling model of relaxation accounts for the main experimental results of the magnetic relaxation in an assembly of interacting fine particles.

The temperature and frequency dependence of thermal dielectric polarization noise was investigated in glycerol and PVC in the vicinity of their glass transitions. Polarization fluctuations were observed via voltage noise which was produced within a sample capacitance cell. The high sensitivity and accuracy of the technique provides a powerful probe of dynamics in low-loss regimes of various materials. Noise spectra had 1/fβ form at lower temperatures just below the glass transition. In glycerol, the spectral exponent decreased smoothly with temperature, extrapolating to 1, i.e. 1/f noise, near T° where relaxation times diverge. The results support the idea that a glassy phase transition occurs in the static limit.

The structure of sodium borate glass was investigated by molecular dynamics simulation using coordination dependent potential model. The simulated alkali borate glass consists of basic units, BO3, triangle, BO4 tetrahedra and structural groups such as boroxol ring and triborate units. The coordination of boron is converted from 3 to 4 by adding alkali oxide.

Fracture in amorphous silica is studied using million-atom molecular dynamics simulations. The dynamics of crack propagation, internal stress fields, and the morphology of fracture surfaces are examined as a function of temperature and strain rate. At 300K and 600K we observe brittle fracture: internal stress increases to a critical value (typically 2 – 3 GPa) and then turns over when the crack reaches a terminal speed on the order of half the Rayleigh wave speed. At 900K crack propagation slows down dramatically due to plastic deformation and the material becomes ductile.

We have investigated the dynamic behavior of liquid crystals (LC), which are not glass formers when in bulk form, confined in porous matrices with randomly oriented, interconnected pores as well as in parallel cylindrical pores with different pore sizes by photon correlation (time range: 20 ns-103s) and dielectric spectroscopies (frequencies: 0.1 Hz-1.5GHz). We observed that in random pores (pore size is 10 nm and 100 nm) LC does not crystallize at temperatures about 25° C below bulk crystallization temperature and the non-Debye relaxational processes studied by both photon correlation and dielectric experiments were found not to be frozen. Slow relaxational process which does not exist in bulk LC and a broad spectrum of relaxation times (10−8 − 10)s appear not only for LC in random pores but in cylindrical pores as well. However in matrices with random pores of 100 Å, glass-like behavior of slow mode (τ > 1ms) was observed. The relaxation time (determined in photon correlation experiment) of this slow process strongly increases when temperature decreases from 300 K up to 270 K varying from 0.2ms to 14 s and it's temperature dependence is described by the Vogel-Fulcher law.

Glass transition and effects of pressure and shear stress on atomic configuration are investigated by means of molecular dynamics simulation. An embedded atom method potential is used for the atomic interaction. A model crystal for Cu is melted and quenched to realize the glass state. Atomic configuration in the glass is examined through the radial distribution function. External stress is applied and displacement of atoms is monitored to investigate the mechanism of mechanical relaxation. Larger displacement of atoms is observed under a shear stress.

We have carried out the molecular dynamics (MD) simulation for a binary soft-sphere system and calculated the self part of the generalized susceptibility χs(q, ω) at various temperatures. At higher temperatures in liquid state, only one peak appears in the imaginary part of Xa, which tends to split into two peaks, the so-called α- and β- peaks, as the temperature is reduced. The temperature dependence of the peak frequency is well described by the Vogel-Fulcher law for the α- peak, and the peak frequency does not change much for the α- peak. We have also measured the trajectory volume of a tagged atom V(t), which is related to the dynamical order parameter, the “generalized capacity”, in structural glass transitions recently proposed by J. F. Douglas. These results show the transition temperature which is in good agreement with that determined by the trapping diffusion model.

A new family of multicomponent metallic alloys exhibits an excellent glass forming ability at moderate cooling rates of about 10K/s and a wide supercooled liquid region. These glasses are eutectic or nearly eutectic, thus far away from the compositions of competing crystalline phases. The nucleation of crystals from the homogeneous amorphous phase requires large thermally activated composition fluctuations for which the time scale is relatively long, even in the supercooled liquid. In the Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy therefore a different pathway to crystallization is observed. The initially homogeneous alloy separates into two amorphous phases. In the decomposed regions, crystallization probability increases and finally polymorphic crystallization occurs. The evolution of decomposition and succeeding primary crystallization in the bulk amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy have been studied by small angle neutron. Samples annealed isothermally in the supercooled liquid and in the solid state exhibit interference peaks indicating quasiperiodic inhomogeneities in the scattering length density. The related wavelengths increase with temperature according to the linear Cahn-Hilliard theory for spinodal decomposition. Also the time evolution of the interference peaks in the early stages is consistent with this theory. At later stages, X-ray diffraction and transmission electron microscopy investigations confirm the formation of nanocrystals in the decomposed regions.

Be diffusivity data in the bulk metallic glass forming alloys Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr46.7Ti8.3Cu7.5Ni10Be27.5 are reported for temperatures between 530K and 710K, extending up to 80K into the supercooled liquid states of the alloys. At the glass transition temperature, Tg, a change in temperature dependence of the data is observed in both alloys, and above Tg the diffusivity increases faster with temperature than below. The data in the supercooled liquid can be described by a modified Arrhenius expression containing the communal entropy of the supercooled liquid and based on a diffusion mechanism suggested earlier. The comparison with viscosity data in the supercooled liquid state of Zr46.7Ti8.3Cu7.5Ni10Be27.5 reveals a breakdown of the Stokes- Einstein relation, whereas D(T) and η(T) follow a relation close to van den Beu-kel's. The breakdown of the Stokes- Einstein relation indicates a cooperative diffusion mechanism in the supercooled liquid state of the ZrTiCuNiBe alloys.

Glasses are generally produced from the highly undercooled liquid state by rapid quenching methods or quasi-statically at slow cooling by the effective control of potent heterogeneous nucleation sites. For metallic systems the latter method recently has led to the development of bulk metallic glass with a complex multicomponent chemistry and advanced engineering properties. With these alloys crystallization can be avoided over a broad temperature / time window. As such, the relevant thermodynamic properties of the metastable glassy and undercooled liquid states can be directly measured below and above the glass transition temperature, respectively. The obtained data give new insight into the nature of the glass transition suggesting that it is not a phase transition in the classical sense but kinetic freezing triggered by an underlying entropie instability to avoid crystallization. Further measurements of the mechanical and wear properties point to the unique engineering properties of these highly disordered materials for technological applications.

Conductivity spectra of crystalline, glassy and molten electrolytes are presented and discussed. The spectra cover fourteen decades on the frequency scale as well as wide temperature ranges. In some crystalline ion conductors, the translational and vibrational contributions to the conductivity are well separated on the frequency scale. This is not observed in glasses and melts. In these cases, the vibrational components can, however, often be removed from the total spectra, yielding the translational component. We find that in crystalline, glassy, and molten electrolytes the conductivity caused by translational motion of the ions exhibits plateaux at both low and high frequencies, with a dispersive regime in between. The dispersive sections of the conductivity isotherms always cover a triangular area in a log-log plot of conductivity times temperature versus frequency. For an interpretation, the jump relaxation model turns out to be appropriate for crystalline electrolytes. The existence of different kinds of site is typical of glasses. For fragile molten electrolytes, a simple semimicroscopic model is presented which explains the experimental findings including the Vogel-Fulcher-Tammann temperature dependence of the dc conductivity.

The motion of structural components in alkali silicates has been studied using molecular dynamic simulations. The relevant time correlation functions have been recorded over periods of up to 0.5 nanoseconds. The van Hove correlation functions reveal that alkali cation diffusion occurs by hopping between rather well defined sites, even at temperatures far above the melting point. The accessibility of such sites is controlled by the relaxation of the surrounding network, and constitutes the mechanism of coupling between the motion of network and modifier elements. The intermediate scattering functions exhibit a stretched exponential behavior, with a wavevector dependent stretching exponent. This is the result of a distribution of residence times at individual cation sites. When the diffusion process is examined on a coarser scale, at which Brownian motion is applicable, this distribution remains undetected. As an alternative to the Kohlrausch function, several mechanistic approaches for describing the relaxation behavior of these structures are discussed.