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Thermodynamic scaling of α-relaxation time and viscosity stems from the Johari-Goldstein β-relaxation or the primitive relaxation of the coupling model
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View: Figures


Image of FIG. 1.
FIG. 1.

Logarithm of characteristic time of dielectric loss maximum of DGEBA (diglycidyl ether of bisphenol-A, M w = 380 g/mol, also known as EPON 828) for α-relaxation and JG-relaxation in isobaric condition versus reciprocal temperature (a), in isothermal condition versus pressure (b), and an overall plot of the same data versus ρ γ/T (c). When not shown, error bars are smaller than symbol size. Black asterisks in panel (c) indicate the values for log10(τ 0) at several state points calculated by the coupling model Eq. (10) with the stretch exponent β K  ≡ (1-n) = 0.52 obtained by fitting the frequency dispersion of the α-relaxation by the Fourier transform of the Kohlrasuch-Williams-Watts function, Eq. (9). Relaxation times and density data at 0.1 MPa are from Ref. 63, relaxation times obtained at high pressure from Ref. 64, PVT data are from Ref. 62. Density data in the glassy state have been extrapolated from the values of glass compressibility and expansivity.

Image of FIG. 2.
FIG. 2.

The inset shows the coupling parameter n changes with T and P at constant structural relaxation time τ α. Data obtained for dipropylene glycol. The main figure shows the consequence of breakdown of ρ γ/T-scaling of τ α.

Image of FIG. 3.
FIG. 3.

Shown in the inset is perfect superpositioning of the dielectric loss spectra of a van der Waals glass-former, PDE, at different combinations of P and T for two given values of constant τ α. Consequently, ρ γ/T-scaling of τ α holds as shown in the main figure.

Image of FIG. 4.
FIG. 4.

Upper panel: Potentials of mean force, W ij(r)s, for the cation-cation pair (blue dashed-dotted curve), anion-anion pair (red dashed curve), and cation-anion pair (green solid curve) obtained at 400 K for EMIM-NO3. A fitted curve in the power law form (r −λ with λ = 11 (red dotted curve)) is shown for cation-anion pair. Lower panel: Corresponding pair correlation functions, g ij(r)s. The power law region ends at distance r λ , where W ij(r) ∼ 0 and g ij(r) ∼ 1.

Image of FIG. 5.
FIG. 5.

Self-part of the van Hove function at 400 K for EMIM+ ions at t = 20, 40, 100, 200, 400, and 1000 ps (from left to right). The function at ∼t dif = 400 ps is colored in pink. Inset shows the MSD of the cation at 400 K.

Image of FIG. 6.
FIG. 6.

Fit by x = Fγ/T) = Aexp(Bργ/T) C to three dynamic quantities and plotted against ρ γ /T with γ = 1.8 for NO3 in CKN obtained by simulation at 0.1 MPa, 0.5 GPa, 1.0 GPa, and 2.0 GPa. Data are not shown. (1) Black line is for the relaxation time τ α of the incoherent intermediate scattering function of anions, and the parameters are A = 30.2 ps, B = 202.5, and C = 4.3. (2) Dashed red line is for T/D, and the parameters are A = 584.4 K × 10−8 m2 s−1, B = 487.1, and C = 1.6. (3) Dashed-dotted blue line is for the product of temperature and reorientational relaxation time, r, and the parameters are A = 402.2 K × ps, B = 408.5, and C = 1.4.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Thermodynamic scaling of α-relaxation time and viscosity stems from the Johari-Goldstein β-relaxation or the primitive relaxation of the coupling model