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arXiv · 0806.1400

Supercooled Liquid Dynamics Studied via Shear-Mechanical Spectroscopy

Claudio Maggi·Bo Jakobsen·Tage Christensen·N. B. Olsen·Jeppe C. Dyre
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Abstract

We report dynamical shear-modulus measurements for five glass-forming liquids (pentaphenyl trimethyl trisiloxane, diethyl phthalate, dibutyl phthalate, 1,2-propanediol, and m-touluidine). The shear-mechanical spectra are obtained by the piezoelectric shear-modulus gauge (PSG) method. This technique allows one to measure the shear modulus ($10^{5} -10^{10}$ Pa) of the liquid within a frequency range from 1 mHz to 10 kHz. We analyze the frequency-dependent response functions to investigate whether time-temperature superposition (TTS) is obeyed. We also study the shear-modulus loss-peak position and its high-frequency part. It has been suggested that when TTS applies, the high-frequency side of the imaginary part of the dielectric response decreases like a power law of the frequency with an exponent -1/2. This conjecture is analyzed on the basis of the shear mechanical data. We find that TTS is obeyed for pentaphenyl trimethyl trisiloxane and in 1,2-propanediol while in the remaining liquids evidence of a mechanical $β$ process is found. Although the the high-frequency power law behavior $ω^{-α}$ of the shear-loss may approach a limiting value of $α=0.5$ when lowering the temperature, we find that the exponent lies systematically above this value (around 0.4). For the two liquids without beta relaxation (pentaphenyl trimethyl trisiloxane and 1,2-propanediol) we also test the shoving model prediction, according to which the the relaxation-time activation energy is proportional to the instantaneous shear modulus. We find that the data are well described by this model.

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Claudio Maggi, Bo Jakobsen, Tage Christensen, N. B. Olsen, Jeppe C. Dyre. 2008-10-03. Supercooled Liquid Dynamics Studied via Shear-Mechanical Spectroscopy. https://doi.org/10.1021/jp805097r

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