The Characteristic Cooling Rate and Vitrification of Liquids

Doklady Physics - This work is devoted to analysis and generalization of the kinetic criteria of vitrification using the model of delocalized atoms. The generalized criterion of a...     

Generalized Kinetic Criterion of the Liquid–Glass Transition

Physics of the Solid State - Justification and generalization of the glass transition criterion of Schmelzer is proposed with the involvement of the model of delocalized atoms. Unlike the...     

Relation between elastic modulus and glass softening temperature in the delocalized atom model

The ratio of softening temperature (glass transition temperature) to elastic modulus (T _g /E) is mainly determined by the limiting elastic deformation of an interatomic bond, which characterizes the transition of a structural microregion from an elastic into a viscous-flow state. In silicate glasses, this transition is caused by the limiting deformation of directed ionic-covalent Si-O-Si bonds. In the case of amorphous hydrocarbons, it is related to the relatively weak intermolecular bonds between regions in chain macromolecules, and the T _g /E ratio is significantly higher than in inorganic glasses. In glassy systems of one class, this ratio turns out to be constant (T _g /E ?? const), and a linear correlation is detected between softening temperature and elastic modulus, which can be explained in terms of the delocalized atom model. The values of T _g /E can be used to classify glasses similarly to the well-known Angell classification according to so-called fragility.     

Cooling rate dependency of fluctuations in the melt volume of amorphous materials

Fluctuations in the melt volume of the amorphous materials as a function of cooling rate is established. The observed dependency is similar to the one found for the glass transition temperature (the Bartenev-Ritland equation). The constant ratio of the empirical parameters in the equation is explained in terms of the excited state model.     

Anharmonicity of lattice vibrations and the fluctuation volume of amorphous substances near the glass transition temperature

The fraction of the fluctuation volume (in a model of the excited state) at the glass transition temperature depends linearly on the Gruneisen parameter, i.e., the degree of the anharmonicity of lattice vibrations in amorphous polymers and glasses.     

Grüneisen parameter and propagation velocities of acoustic waves in vitreous solids

A linear correlation has been found between the Grüneisen parameter and the ratio of the propagation velocities of longitudinal and transverse acoustic waves in vitreous solids. The relation between these quantities has been interpreted in terms of the Pineda model.     

Anharmonism of lattice vibrations and of acoustic wave propagation velocity in quasi-isotropic solids

Linear correlation is established in glasses between the Grüneisen parameter and the ratio of propagation velocities of the longitudinal and transverse acoustic waves. An interpretation is given within the Pineda-Kuz’menko model to the relation between the harmonic and anharmonic quantities.     

On the molecular mobility in amorphous polymers, inorganic glasses, and amorphous metal alloys in the glass transition range

The transition of kinetic units (atoms or groups of atoms) in amorphous media from one quasi-equilibrium state to another is determined by fluctuations of both energy and entropy of the system. In the glass transition range of liquids and polymers, the entropic mechanism plays a determining role: the fluctuation of packing of particles turns out to be more important than accumulation of energy. Above the glass transition range, the energy mechanism begins to play a dominant role. The procedure that is currently used to calculate the constant for the Bartenev equation, which relates the relaxation time to the cooling rate at the glass transition temperature, leads to overestimated values. A procedure for the calculation of this parameter was proposed with allowance for the temperature dependence of the entropy of activation in the region of the liquid-glass transition. The use of this equation in the relaxation spectrometry of amorphous polymers, inorganic glasses, and amorphous metal alloys is discussed.     

Elastic moduli and poisson ratio for amorphous polymers and glasses

We propose that the product of the density by the square of the rms velocity of strain waves, which exhibits the features typical of elastic moduli, be referred to as effective (or characteristic) elastic modulus. The ratio of the bulk compression modulus to the effective elastic modulus is a single-valued function of the Poisson ratio not only for crystals and glasses, but also for amorphous organic polymers. The effective elastic modulus may be helpful in analysis of anharmonism of lattice vibrations of deformable bodies.     

On the relaxation theory of glass transition in liquids

A method for calculating the constant in the main equation of glass transition (which relates the relxation time and the cooling rate near the glass transition temperature) with consideration given to the temperature dependence of the activation energy in this region is proposed. A modification of the main glass transition equation is considered. Application of this equation to the relaxation spectrometry of amorphous polymers and inorganic glasses is discussed.