Dynamics of glass-forming liquids. III. Comparing the dielectric α- and β-relaxation of 1-propanol and o-terphenyl

Hansen, C.; Stickel, F.; Berger, T.; Richert, Ranko; Fischer, Erhard W.

doi:10.1063/1.474456

Cited by 405 publications

(428 citation statements)

References 38 publications

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“…39,40 There has been experimental evidence from other studies 21,[41][42][43] that indicate the lack of merit in the arguments presented. 41,42 Moreover, dielectric relaxation of a variety of unbranched monohydric alcohols has also been studied in n-alkane solutions at 298 K and 1 MHz-18 GHz frequency range by Schwerdtfeger, et al 44 and the observed Debye relaxation time has been discussed in terms of the usual wait-and-switch model of relaxation in which hydrogen bonds break and then reform.…”

Section: Structure Of the Liquid And The Relaxation Processesmentioning

confidence: 94%

Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Power¹,

Vij²,

Johari³

2007

The Journal of Chemical Physics

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To gain insight into the effects of liquid-liquid phase separation on molecular relaxation behavior we have studied an apparently homogeneous mixture of 5-methyl-2-hexanol and isoamylbromide by dielectric spectroscopy over a broad temperature range. It shows two relaxation regions, widely separated in frequency and temperature, with the low-frequency relaxation due to the alcohol and the high-frequency relaxation due to the halide. In the mixture, the equilibrium dielectric permittivity s of the alcohol is 41% of the pure state at 155.7 K and s of isoamylbromide is ϳ86% of the pure state at 128.7 K. The difference decreases for the alcohol component with decreasing temperature and increases for the isoamylbromide component. The relaxation time of 5-methyl-2-hexanol in the mixture at 155.7 K is over five orders of magnitude less than in the pure state, and this difference increases with decreasing temperature, but of isoamylbromide in the mixture is marginally higher than in the pure liquid. This shows that the mixture would have two T g 's corresponding to its of 10 3 s, with values of ϳ121 K for its 5-methyl-2-hexanol component and ϳ108 K for its isoamylbromide component. It is concluded that the mixture phase separates in submicron or nanometer-size aggregates of the alcohol in isoamylbromide, without affecting the latter's relaxation kinetics, while its own s and decrease markedly.

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Section: Structure Of the Liquid And The Relaxation Processesmentioning

confidence: 94%

Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Power¹,

Vij²,

Johari³

2007

The Journal of Chemical Physics

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“…I, there is only one relaxation process in the lowviscosity liquid at GHz frequencies. [3][4][5][6][7][8] As the liquid is cooled and its density and viscosity increase, this relaxation process shifts to lower frequencies. After a certain density and viscosity has been reached on supercooling, the ␣-relaxation process emerges from the low-frequency side of the ␤-relaxation peak and rapidly gains strength at the expense of the original relaxation process observed at GHz frequencies, which now becomes the faster relaxation.…”

Section: F the Origin Of The ␤-Relaxation Processmentioning

confidence: 99%

“…11-13͑c͒ Since the relaxation rate of the ␤ process, f m,␤ , has shown an Arrhenius-type temperature dependence, [3][4][5][6][7][8] except for those in the recent studies on three glasses, where the slope of the plot increases on cooling at T near T g , 22,23 we may consider that for at least TϽT g , neither the decrease in the configurational entropy associated with the ␤-relaxation process, S conf,␤ , nor that associated with the unfrozen modes of the ␣-relaxation process, affects the ␤-relaxation kinetics. 13͑c͒ In the entropy theory, a decrease in the net configurational entropy is seen to affect the ␣-relaxation kinetics.…”

Section: Entropy and Localized Molecular Motionsmentioning

confidence: 99%

“…6 Thus, molecular diffusion in a low-viscosity liquid occurs mainly by the mechanism of the ␤-relaxation process, and at high viscosity it occurs by the mechanisms of both the ␤-, and the ␣-relaxation processes. 7,8 In glasses, ␤ relaxation alone is observed in the usual laboratory time scale experiments. Thus, the contribution to permittivity due to orientational polarization in the low-viscosity liquid is only due to the ␤-relaxation process, and in a viscous liquid and glass, it is equal to the sum of the contributions to permittivity from the ␣-, and ␤-relaxation processes, or (⌬⑀ ␣ ϩ⌬⑀ ␤ ), with dielectric relaxation strengths of ⌬⑀ ␣ and ⌬⑀ ␤ , respectively.…”

Section: Introductionmentioning

confidence: 99%

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Localized relaxation in a glass and the minimum in its orientational polarization contribution

Johari

Power

Vij

2002

The Journal of Chemical Physics

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The dielectric permittivity and loss spectra of the glassy state of 5-methyl-2-hexanol obtained by quenching it from the liquid state has been studied. In one experiment, the spectra were studied at different temperatures as the quenched sample was heated at 0.1 K/min from 105.3 to 160.5 K. In the second experiment, the quenched sample was heated from 77 to 131.6 K and kept at that temperature for 14.6 ks. The relaxation rate, f m,␤ , the dielectric relaxation strength, ⌬⑀ ␤ , and the distribution of relaxation time parameters, ␣ and ␤, for the Johari-Goldstein process were determined. The parameter ␤ was found to be equal to 1 and independent of both the temperature and time, ⌬⑀ ␤ initially decreased on increasing the temperature, reached a minimum value at ϳ145.6 K, and then increased. The plot of f m,␤ against the reciprocal temperature decreased in slope and at ϳ140 K became linear. This indicates that f m,␤ increases on structural relaxation. In the course of the annealing at 131.6 K, ⌬⑀ ␤ of the quenched sample decreased with time, approaching a plateau value. It is described by an equation, ⌬⑀ ␤ (t)ϭ⌬⑀ ␤ (t→ϱ)ϩ͓⌬⑀ ␤ (tϭ0)Ϫ⌬⑀ ␤ (t →ϱ)͔exp͓Ϫ(t/ )͔, where t is the time, and ͑ϭ3.5 ks͒ is the characteristic time. It is pointed out that contrary to the earlier finding, o-terphenyl shows a ␤ relaxation in the equilibrium liquid state. A consideration of dielectric permittivity arising from small-angle motions of all molecules, which has been suggested as an alternative mechanism for the localized motions seen as ␤ relaxation, indicates that this mechanism is inconsistent with the known increase in the equilibrium permittivity on cooling.

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“…(iii) Johari-Goldstein type β-process (secondary process in the context of dielectric relaxation) [8,9,10,11,12,13] merges into the α-relaxation around T D , extrapolating the Arrhenius-type temperature dependence below T g of the β-relaxation times [6,14,15,16,17,18,19].…”

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confidence: 99%

Merging of α and slow β relaxation in supercooled liquids

2002

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Dielectric relaxation spectroscopy (1 Hz -20 GHz) has been performed on supercooled glassformers from the temperature of glass transition (Tg) up to that of melting. Precise measurements particularly in the frequencies of MHz-order have revealed that the temperature dependences of secondary β-relaxation times deviate from the Arrhenius relation in well above Tg. Consequently, our results indicate that the β-process merges into the primary α-mode around the melting temperature, and not at the dynamical transition point T ≈ 1.2Tg.PACS numbers: 64.70. Pf, 77.22.Gm, In recent years, much of the focus on glassy dynamics has been shifting to a considerably higher temperature than T g , the glass-transition one [1,2,3,4]. The topical temperature is located around T D ≡ 1.2T g , where the dynamics of supercooled liquids has been found to change fairly. So far, there have been observed the following phenomena:(i) Rössler scaling reveals that, when cooled, the Debye-Stokes-Einstein relation becomes invalid around T D [5,6]. This indicates a change of diffusion mechanism there.(ii) Stickel analysis [7] clarifies that temperature dependence of viscosity changes around T D . Therefore, in order to fit the primary α-relaxation time τ α using the Vogel-Fulcher-Tamman (VFT) relation,the coefficients (τ 0 , C, T 0 ) have to vary at T B ≈ T D . This suggests that the mechanism of slow structural-relaxation makes some alternation there.(iii) Johari-Goldstein type β-process (secondary process in the context of dielectric relaxation) [8,9,10,11,12,13] merges into the α-relaxation around T D , extrapolating the Arrhenius-type temperature dependence below T g of the β-relaxation times [6,14,15,16,17,18,19].Theoretically, the characteristic temperature T D is thought to be comparable to T C where the idealized Mode Coupling Theory (MCT) predicts a dynamical phase transition [20]. Indeed, the above first two phenomena (i, ii) can be regarded as indicators of the dynamical transition at T C . However, the MCT is irrelevant to the third one (iii), the bifurcation of α, β-modes; even the existence of the Johari-Goldstein type β-process cannot be derived.Furthermore, from experimental aspects, while the dynamical transition phenomena (i, ii) have been confirmed from either Rössler or Stickel plot definitely, the bifurcation of (iii) is inferred from the extrapolation. Actually, however, it remains an open problem as to whether the Arrhenius behavior of the β-process persists in higher temperatures near T D : the T D -decoupling of α, β-relaxations is not conclusive.This letter thus aims to investigate the secondary β-mode in high temperatures well above T g , by carrying out precisely the broad-band measurements of dielectric relaxation. Our main result is the following: as will be seen in Figures 2 and 5, the β-relaxation times deviate from the Arrhenius relation, indicating that the β-relaxation merges into the α-mode not at T D but around the Arrhenius-VFT crossover temperature T A (generally close to the melting one) where the temperatu...

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Dynamics of glass-forming liquids. III. Comparing the dielectric α- and β-relaxation of 1-propanol and o-terphenyl

Cited by 405 publications

References 38 publications

Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Localized relaxation in a glass and the minimum in its orientational polarization contribution

Merging of α and slow β relaxation in supercooled liquids

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