The instantaneous shear modulus in the shoving model

Abstract

Model for the alpha and beta shear-mechanical properties of supercooled liquids and its comparison to squalane data The Journal of Chemical Physics 146, 154504 (2017) We point out that the instantaneous shear modulus G ∞ of the shoving model for the non-Arrhenius temperature dependence of viscous liquids' relaxation time is the experimentally accessible highfrequency plateau modulus, not the idealized instantaneous affine shear modulus that cannot be measured. Data for a large selection of metallic glasses are compared to three different versions of the shoving model. The original shear-modulus based version shows a slight correlation to the Poisson ratio, which is eliminated by the energy-landscape formulation of the model in which the bulk modulus plays a minor role.

Maxwell relaxation time for nonexponential α‐relaxation phenomena in glassy systems

“…Specific procedures for this measurement technique are detailed in Guerette et al It is worth noting that the experimentally measured shear moduli here are, strictly speaking, the plateau moduli and not the unrelaxed instantaneous shear modulus that appears in the Maxwell relation. However, this should not affect the final outcome owing to the fact that both moduli are the same order of magnitude while the relaxation time changes by several orders of magnitude for a given temperature range . The shear modulus was measured over temperatures ranging between 303 and 1273 K for samples with different fictive temperatures.…”

“…However, this should not affect the final outcome owing to the fact that both moduli are the same order of magnitude while the relaxation time changes by several orders of magnitude for a given temperature range. 38,39 The shear modulus was measured over temperatures ranging between 303 and 1273 K for samples with different fictive…”

Connection between fragility, mean-squared displacement, and shear modulus in two van der Waals bonded glass-forming liquids

“…(6) and (2)). To establish whether a plateau in the real part of the shear modulus is actually reached is not easy 50 , especially for higher temperatures within the frequency range of this setup. However, if a liquid obeys TTS, i.e., the spectral shape does not change with time and temperature, given the Kramers-Kronig relations between the real and imaginary part of the shear modulus, the plateau of the elastic shear modulus is proportional to the maximum loss, G ∞ (T ) ∝ G max (T ), i.e., they have the same temperature dependence 35 .…”

Incremental viscosity by non-equilibrium molecular dynamics and the Eyring model

“…The Newtonian viscosity acts as a coefficient or reference state whose temperature dependence is often assumed to follow an activation energy or Arrhenius dependence although there are a number of alternative assumed flow mechanisms proposed in the literature which also give rise to the same inverse temperature dependence but do not invoke the concept of activated dynamics. Notably there is the so-called "shoving model," [39][40][41][42][43] in which stress relaxation is taken to be caused by elastic deformation and ensuing structural rearrangement of the cage of molecules around an arbitrary molecule. The Arrhenius activation energy in the shoving model is replaced by the product of G p , the plateau modulus (which is slightly lower than the true infinite frequency modulus, G ∞ ), and Ω c , a characteristic volume of order of the molecular volume or smaller.…”