Thermo-Rheological, Piezo-Rheological, and TV^γ-Rheological Complexities of Viscoelastic Mechanisms in Polymers

Abstract

Experimental evidence are collected together to show in general the viscoelastic mechanisms of low and high molecular weight polymers have different dependences on temperature T, pressure P, and the same scaling product variable, TV γ , where V is the specific volume and γ is a material constant. The viscoelastic mechanisms include the Johari−Goldstein β-relaxation, the segmental α-relaxation, the sub-Rouse modes, the Rouse modes, and the terminal relaxation if the polymer chains are entangled. Appropriately called the thermo-, piezo-, and TV γ -rheological complexity of polymers, these viscoelastic anomalies are fundamental and deserve attention from the polymer physics community. Although we show that the coupling model can rationalize the origin of the complexity and explain some of the data quantitatively, the objective of this paper is to stimulate others to construct a theory that can do even better.

Corroborative evidences of TVγ-scaling of the α-relaxation originating from the primitive relaxation/JG β relaxation

“…[35], and further developed in Ref. [63]. Here we point out from experiment 34 More recently, the property of TV γ -scaling with the same  for different variables is found by molecular dynamics simulation in two very different materials, and again it can be explained by TV γ -scaling originating at the primitive/JG -relaxation level.…”

“…[35], and further developed in Ref. [63]. Here we point out from experiment 34 that, at fixed value of the relaxation time of n(T,P) or   (T,P), the shape of the relaxation peak for either the normal mode or the -relaxation is constant.…”

Exploring the glass transition region: crowding effect, nonergodicity and thermorheological complexity

“…Each simulation box contains 16 chains, each with 20 beads. Each system was then equilibrated for 10 5 MC steps during which several physical quantities were monitored. The production runs comprise another 10 5 MC steps of the equilibrated configurations.…”

“…The unexplained part of the thermorheological complexity and exact quantification of the nonergodicity in influencing the glassy relaxation behavior need further detailed investigations in the near future, as echoed by Ngai and Plazek in their recent paper. 5 Appendix I…”

“…Similarly, both the dynamic moduli G 0 (o) and G 00 (o) can be expressed as analytical functions in terms of the relaxation modulus G(t) and creep compliance J(t). 2 The time-temperature superposition principle [3][4][5] is a general tool for the description of viscoelastic behavior of linear polymers over a wide range of time (or frequency). The temperature dependence of the viscoelastic response of a polymer melt incorporates a short-time (high frequency) and a long-time (low frequency) region.…”