Dielectric and shear mechanical alpha and beta relaxations in seven glass-forming liquids

Jakobsen, Bo; Niss, Kristine; Olsen, Niels Boye

doi:10.1063/1.2136887

Cited by 102 publications

(80 citation statements)

References 33 publications

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“…Figure 3(a) shows a minimum-slope evolution with loss peak frequency. It can be seen that it is similar to temperature data at ambient pressure [17,18,33], the high frequency slope of the dielectric dissipation may converge slowly to −1/2 as pressure increases.…”

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Pressure dependence of the dielectric loss minimum slope for ten molecular liquids

Nielsen

Pawlus

Paluch

et al. 2008

Philosophical Magazine

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To cite this version:Albena Ivanova Nielsen, Sebatian Pawlus, Marian Paluch, Jeppe Dyre. Pressure dependence of the dielectric loss minimum slope for ten molecular liquids. Philosophical Magazine, Taylor & Francis, 2008, 88 (33-35) We present a comprehensive study of data for the dielectric relaxation of ten glass-forming organic liquids at high pressure along isotherms, showing that the primary (α) high frequency relaxation is characterized well by the minimum slope and the width of the loss peak. The advantage of these two parameters is that they are model independent. For some materials with β processes in mHz and kHz range the high frequency slope tends to be −1/2 with pressure increase. Besides the two parameters captures the relaxation shape invariance at given relaxation time but different combinations of pressure and time [6].Glass may be regarded as the fourth state of conventional matter, isotropic as the liquid state, but solid as the crystalline state. With the notable exception of helium, any liquid may be turned into glass by cooling it fast enough to avoid crystallization [1][2][3][4][5].Physical systems usually relax following perturbations forced upon them. The relaxation of the systems consists of processes going on different time scales. The dominant and slowest relaxation process of a glass-forming liquid is the so-called α process. The α process defines the liquid relaxation time, an important quantity because the glass transition takes place when the relaxation time significantly exceeds the inverse relative cooling rate. Compression of supercooled liquid slows down the α relaxation (increases the characteristic relaxation time, τ ). On the other hand this effect can be compensated by heating up the liquid. Different combinations of p and T can result in the same relaxation dynamics at same τ or materials obey the temperature-pressure superposition at the same relaxation times (TTPS) [6][7][8][9][10][11]. There are differnet kinds of secondary (β) relaxation including the Johari-Goldstein (JG) and these of intra-molecular motions [11][12][13][14][15][16] or any excess wings.In a paper from 2001 it was shown that the high frequency slope of the dielectric loss for a group of materials tends to be −1/2 as the temperature approaches the glass transition temperature, T → T g , and this was linked to time-temperature superposition (TTS) [17], but there is found a general prevalence of the −0.5 for the slope in highly viscous liquids no matter if TTS is obeyed [18]. In those papers the dielectric scans were taken at ambient pressure. In the following is investigated: if this result holds for dielectric frequency scans for ten liquids along isotherms with increasing pressure (p → p g ) ; and if the used model-independent shape quantities, minimum slope and half loss peak width capture TTPS. The minimum slope, of course, may well be affected by secondary processes, the well expressed in the experimental frequency window as well the underlying low-frequency β relaxation * Corresponding author. Emai...

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confidence: 63%

Pressure dependence of the dielectric loss minimum slope for ten molecular liquids

Nielsen

Pawlus

Paluch

et al. 2008

Philosophical Magazine

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“…4(a) and 4(b). 2E1H is a paradigmatic monoalcohol which is known to exhibit a supra-molecular relaxation clearly seen as distinct slow mode in the mechanical spectra as well as a strong Debye signal in the dielectric spectra [36], while DC704 is a van der Waals liquid with no additional modes and a "simple" behavior in general [50,51]. As observed in Fig.…”

Section: B Spectral Shape and Slow Modementioning

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Slow rheological mode in glycerol and glycerol–water mixtures

Jensen

Gainaru

Alba‐Simionesco

et al. 2018

Phys. Chem. Chem. Phys.

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Glycerol-water mixtures were studied at molar concentrations ranging from x gly = 1 (pure glycerol) to x gly = 0.3 using shear mechanical spectroscopy. We observed a low frequency mode in neat glycerol, similar to what is usually reported for monohydroxy alcohols. This mode has no dielectric counterpart and disappears with increased water concentration. We propose that the hydrogen-bonded network formed between glycerol molecules is responsible for the observed slow mode and that water acts as a plasticizer for the overall dynamics and as a lubricant softening the hydrogen-bonding contribution to the macroscopic viscosity of this binary system.

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“…Samples were prepared by squeezing liquid tetramethyl tetraphenyl trisiloxane (trade name DC704, glass transition temperature [23] T g ≈ 210 K, commonly used as diffusion pump oil) between two optically clear substrates, a generation side substrate which held a 33 nm aluminum transducer film and a detection side substrate. See the inset in Fig.…”

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confidence: 99%

Nonlinear Acoustics at GHz Frequencies in a Viscoelastic Fragile Glass Former

et al. 2015

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Using a picosecond pump-probe ultrasonic technique, we study the propagation of high-amplitude, laser-generated longitudinal coherent acoustic pulses in the viscoelastic fragile glass former DC704. We observe an increase of almost 10% in acoustic pulse propagation speed at the highest optical pump fluence which is a result of the supersonic nature of nonlinear propagation in the viscous medium. From our measurement, we deduce the nonlinear acoustic parameter of the glass former in the gigahertz frequency range across the glass transition temperature. DOI: 10.1103/PhysRevLett.114.065701 PACS numbers: 64.70.P-, 62.50.-p, 62.60.+v The observation of laser-driven shock wave propagation provides direct experimental access to the equations of state of strongly compressed materials. This information is of paramount importance for geophysics, astrophysics [1], and inertial confinement fusion [2]. For many years, measurements of shock velocities have been possible through transit time measurements [3]. Only recently, single-shot optical velocity interferometry [2,4-9] allowed direct access to the dynamics of shock front motion in transparent solids but has been restricted to experimental configurations where the shock transforms the medium into a new, highly reflecting phase. Through this technique, the decay of both plane [4,7] and convergent [9,10] shocks with pressures exceeding tens of GPa have been reported. The propagation of shock waves in soft transparent materials such as polycarbonate and PMMA has been observed by single-shot ultrafast dynamic ellipsometry [11,12], a method allowing the separation of pressureinduced variations in elastic and optical properties. In such materials, characteristic pressures ranged from a few to 10-20 GPa, and acoustic Mach numbers defined as M A ¼ u=v 0 , where u is the particle velocity and v 0 the linear acoustic velocity, were subsonic in the range 0.2 < M A < 0.9. Very recently, the propagation of weak shock waves with Mach numbers M A < 0.1 and pressures below the damage threshold of the sample has been observed in thin sapphire slabs through ultrafast optical reflectivity [13], in a 4:1 methanol-ethanol mixture in a diamond anvil cell by ultrafast velocity interferometry [14], in a piezoelectric thin film through terahertz spectroscopy [15], and in a gold film through ultrafast plasmon interferometry [16] and ultrafast optical imaging [17]. In such weakly nonlinear acoustics experiments [18], no variation of the weak shock wave velocity during propagation has been reported to date. In a different manner, an indication for the nonlinearity of picosecond acoustic pulses with Mach numbers 0.0007 < M A < 0.0018 and their decay within 1-3 mm propagation distances has been observed by classical Brillouin spectroscopy [19] through measurement of the distribution of 22 GHz longitudinal phonons along the acoustic pulse trajectory. In such experiments, information on wide-frequency-band nonlinear waves is obtained from the spatial distribution of a single Brillouin frequency compo...

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Dielectric and shear mechanical alpha and beta relaxations in seven glass-forming liquids

Cited by 102 publications

References 33 publications

Pressure dependence of the dielectric loss minimum slope for ten molecular liquids

Pressure dependence of the dielectric loss minimum slope for ten molecular liquids

Slow rheological mode in glycerol and glycerol–water mixtures

Nonlinear Acoustics at GHz Frequencies in a Viscoelastic Fragile Glass Former

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