9 research outputs found
Dynamic thermal expansivity of liquids near the glass transition
Based on previous works on polymers by Bauer et al. [Phys, Rev. B (2000)],
this paper describes a capacitative method for measuring the dynamical
expansion coefficient of a viscous liquid. Data are presented for the
glass-forming liquid tetramethyl tetraphenyl trisiloxane (DC704) in the
ultraviscous regime. Compared to the method of Bauer et al. the dynamical range
has been extended by making time-domain experiments and by making very small
and fast temperature steps. The modelling of the experiment presented in this
paper includes the situation where the capacitor is not full because the liquid
contracts when cooling from room temperature down to around the
glass-transition temperature, which is relevant when measuring on a molecular
liquid rather than polymer
Communication:Two measures of isochronal superposition
A liquid obeys isochronal superposition if its dynamics is invariant along
the isochrones in the thermodynamic phase diagram (the curves of constant
relaxation time). This paper introduces two quantitative measures of isochronal
superposition. The measures are used to test the following six liquids for
isochronal superposition: 1,2,6 hexanetriol, glycerol, polyphenyl ether,
diethyl phthalate, tetramethyl tetraphenyl trisiloxane, and dibutyl phthalate.
The latter four van der Waals liquids obey isochronal superposition to a higher
degree than the two hydrogen-bonded liquids. This is a predic- tion of the
isomorph theory, and it confirms findings by other groups.Comment: 14 pages (article 4 pages, supplementary 10 pages), 42 figure
Frequency Dependent Bulk Modulus of a Number of Molecular Liquids Measured Using the Piezo-Electric Bulk Modulus Gauge
The dynamic bulk modulus of three glass-forming liquids
We present dynamic adiabatic bulk modulus data for three organic glass-forming liquids: two van der Waal's liquids, trimethyl-pentaphenyl-trisiloxane (DC705) and dibuthyl phtalate (DBP), and one hydrogen-bonded liquid, 1,2-propanediol (PD). All three liquids are found to obey time-temperature superposition within the uncertainty of the measurement in the adiabatic bulk modulus. The bulk modulus spectra are compared to the shear modulus spectra. The time scales of the two responses were found to be similar. The shapes of the shear and bulk modulus alpha loss peak are nearly identical for DBP and DC705, while the bulk modulus spectrum for PD is significantly broader than that of the shear modulus. The data further suggest that a "bulk modulus version of the shoving model" for the temperature dependence of the activation energy using the bulk modulus relaxation strength, K(T), works well for DC705 and DBP, but not PD, while a formulation of the model using the high-frequency plateau value, K ∞ (T), gave a poor result for all three liquids. © 2014 AIP Publishing LLC. [http://d