Anharmonicity and the elementary event of plastic deformation of amorphous polymers and glasses

The critical displacement of an excited atom (group of atoms) corresponding to the maximum in the interatomic attraction force plays an important part in the elementary event of plastic deformation of glassy solids. As a result of considerable departure of the excited kinetic unit from the equilibrium position and the nonlinearity of the interatomic interaction force, the microdeformation in the elementary event turns out to be a function of the degree of anharmonicity (Grüneisen parameter).     

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...     

Estimation of the parameter of the main equation of the glass transition of amorphous polymers and other amorphous substances

Parameter C from the main glass-transition equation qτ_g = C according to Nemilov’s theory has the meaning of temperature bandwidth δT_g in which the freezing of the structure of the glass-forming liquid occurs (where q is the cooling rate of a melt and δ_g is the time of structural relaxation at the glass-transition temperature). The currently used method to estimate C results in inflated values, a circumstance that is due to the assumption of the constancy of the activation energy of the glass transition in the derivation of the calculation formula. Methods of estimation of C that are in agreement with the experimental data have been considered. A calculation of the time of structural relaxation, δ_g, on the basis of the values of the parameters of the Williams–Landel–Ferry equation has been proposed.     

Melting temperature and anharmonicity of lattice vibrations in solids

A correlation between melting points and Grüneisen lattice constants was found for a number of glass-forming oxides. It was established that, at the melting point, the mean energy of the thermal motion of a kinetic unit equaled the ultimate strain work of the interatomic bond corresponding to the quasi-elastic force maximum.     

The elementary softening event in glassy systems in terms of the model of the excited state

The pressure dependence of the glass-transition temperature (glass-transition lines) is described through a relationship similar to the Clausius-Clapeyron equation. The criterion for the glass-liquid transition for polymer and other glasses is calculated. According to the proposed speculations, an elementary softening event in glasses is reduced to the critical deformation of interatomic (intermolecular) linkage, which corresponds to the maximum force of attraction between atoms. A glass (an amorphous polymer) softens when the mean energy of the thermal motion of the kinetic units responsible for the viscous flow is ∼3 times higher than the work of the ultimate deformation of the interatomic bond. The nature of structural changes occurring in the course of critical displacement (excitation) of kinetic units in liquids and glasses is discussed.     

Coefficient of transverse deformation and anharmonism of lattice oscillations in quasi-isotropic solids

The dependence of the Grüneisen parameter γ _D on the anharmonism of lattice oscillations is controlled by γ₃ that appears to be a single-value function of the Poisson coefficient. In terms of γ _D -γ₃ relationship, all solids can be grouped into different structural types. Within each group, the above relationship is linear. The nature of correlation between the Grüneisen parameter and the Poisson coefficient is discussed.     

On the Grüneisen parameter for crystals and glasses

Additional data confirming the close relation between the Grüneisen parameter and the Poisson ratio are obtained. The estimate of the Grüneisen parameter based on the Leont’ev formula using the data on density, bulk compression modulus, and velocity of sound is in conformity with the results of calculations based on the Grüneisen and Belomestnykh-Tesleva equations.     

Poisson ratio and plasticity of glasses

Analysis of experimental data reveals a regular relation between Poisson’s ratio and plastic characteristics of inorganic glasses.     

The Grüneisen parameter and Poisson coefficient for glassy organic polymers and inorganic glasses

The Grüneisen lattice parameter has been calculated from the data on the Poisson coefficient for amorphous polymers and glasses. For glassy polymers, the thermodynamic Grüneisen parameter characterizes anharmonicity averaged over intrachain and other vibrational modes, the Grüneisen lattice parameter defines anharmonicity of interchain interactions provided by intermolecular interactions. In the case of alkali silicate glasses, the Grüneisen lattice parameter reflects the anharmonicity of vibrations of ionic sublattice that is formed by alkali-metal ions and nonbridging oxygen atoms.     

Anharmonicity of lattice vibrations and transverse deformation of crystalline and vitreous solids

This paper reports on the additional data confirming the interrelation between the Grüneisen parameter and Poisson’s ratio in crystalline and vitreous solids. The assumption is made that the ratio between the velocities of longitudinal and transverse acoustic waves can depend on the anharmonicity of lattice vibrations.