Gruneisen parameter and fluctuation volume of amorphous polymers and glass

Abstract

The Gruneisen parameter of glassy polymers and inorganic glass is a linear function of the fraction of the fluctuation volume that is frozen at the glass transition temperature. The nature of an interrelation between linear and nonlinear properties of solids, in particular, between the Gruneisen parameter and Pois son's ratio is discussed. F F m r 0 0 x m = Δr m x = r -r 0

NVUperspective on simple liquids’ quasiuniversality

“…Thus for viscous simple liquids the quantity a 2 / x 2 identifies Ω and, in this sense, "controls" the relaxation time in the same sense as entropy does. This is an old idea [140][141][142][143][144][145][146][147], which is closely related to the reasoning behind the shoving model and other elastic models for the temperature dependence of viscous liquids' relaxation time [109,[148][149][150]. Note also that, since 1/ x2 identifies Ω, for simple liquids the crossover to activated transitions takes place at a quasiuniversal value of the reduced-unit vibrational displacement x2 , as recently predicted by Lubchenko and coworkers from the random first-order transition theory [151,152].…”

Stress effects on the elastic properties of amorphous polymeric materials

“…On the contrary, the observed increase indicates that, because of the tensile stress, the systems experienced a softening of the elastic moduli. This behavior is in agreement with the positive value of the Grüeneisen parameters for polybutadiene and epoxy resins 31,32 implying markedly nonlinear features, and in particular an increase of the moduli with the increase of density which overcompensates the pure density effect on the sound velocities.…”

Free Volumes and Grüneisen Parameters in Mixed‐Tacticity Polyhydroxybutyrates

“…[ 5 ] The fractional free volumes , Figure 3, are in agreement with values of the fractional thermal atomic fluctuation volume determined for a variety of polymers. [ 13 ] The show a trend toward increasing values with decreasing . Its progression with is similar to that of , since up to K, is caused by thermal expansion, as expressed by Equation ().…”

“…pointed out that, in glasses from the same class of materials, there is a proportionality between the free ('fluctuation') volume and . [ 13 ] In our previous work, the modelled amorphous‐phase elastic moduli decreased from 1.08 GPa to 0.23 GPa from to (Figure 16b in the cited article). [ 7 ] Hence, in this work and due to their manner of calculation via Equation (), the values of for the amorphous phase decreased from 0.4 to 0.1 over the same range.…”

“…In both cases, a prominent delineation is between interchain lattice‐ (low , high ) and intrachain thermodynamic (high , low ) motions. [ 13 ] Curro and Gibbons, respectively, demonstrated that in polymers and at low temperatures, , since translational chain motions (acoustic modes) dominate the heat capacity. [ 14,15 ] At high temperatures, the rotational and vibrational contributions (optic modes) lead to .…”