Communication: Direct tests of single-parameter aging

This paper presents accurate data for the physical aging of organic glasses just below the glass transition probed by monitoring the following quantities after temperature up and down jumps: the shear-mechanical resonance frequency (around 360 kHz), the dielectric loss at 1 Hz, the real part of the dielectric constant at 10 kHz, and the loss-peak frequency of the dielectric beta process (around 10 kHz). The setup used allows for keeping temperature constant within 100 micro Kelvin and for thermal equilibration within a few seconds after a temperature jump. The data conform to a new simplified version of the classical Tool-Narayanaswamy aging formalism, which makes it possible to calculate one relaxation curve directly from another without any fitting to analytical functions

Rheological model for the alpha relaxation of glass-forming liquids and its comparison to data for DC704 and DC705

Dynamic shear-modulus data are presented for the two silicone oils DC704 and DC705 for frequencies between 1 mHz and 10 kHz at temperatures covering more than five decades of relaxation-time variation. The data are fitted to the alpha part of a phenomenological model previously shown to describe well the dynamic shear modulus of squalane, which has a large beta process [Hecksher \textit{et al.}, J. Chem. Phys. \textbf{146}, 154504 (2017)]; that model is characterized by additivity of the alpha and beta shear compliance and by a high-frequency decay of the alpha process in proportion to $\omega^{-1/2}$ in which $\omega$ is the angular frequency. The fits of the alpha part of this model to the DC704 and DC705 data are compared to fits by a Havriliak-Negami type model, the Barlow-Erginsav-Lamb model, and a Cole-Davidson type model. At all temperatures the best fit is obtained by the alpha part of the squalane model. This strengthens the conjecture that so-called $\sqrt{t}$-relaxation, leading to high-frequency decays proportional to $\omega^{-1/2}$, is a general characteristic of the alpha relaxation of supercooled liquids [Dyre, Phys. Rev. E {\bf 74}, 021502 (2006); Nielsen \textit{et al.}, J. Chem. Phys. \textbf{130}, 154508 (2009); Pabst \textit{et al.}, J. Phys. Chem. Lett. \textbf{12}, 3685 (2021)]

An energy landscape model for glass-forming liquids in three dimensions

We present a three-dimensional lattice-gas model with trivial thermodynamics, but nontrivial dynamics. The model is characterized by each particle having its own random energy landscape. The equilibrium dynamics of the model were investigated by continuous time Monte Carlo simulations at two different densities at several temperatures. At high densities and low temperatures the model captures the important characteristics of viscous liquid dynamics. We thus observe non-exponential relaxation in the self part of the density auto-correlation function, and fragility plots of the self-diffusion constant and relaxation times show non-Arrhenius behavior.Comment: 6 pages, 6 figures, Submitted for proceedings of the 5th IDMRC

Generalized single-parameter aging tests and their application to glycerol

Physical aging of glycerol following temperature jumps is studied by dielectric spectroscopy at temperatures just below the glass transition temperature. The data are analyzed using two single-parameter aging tests developed by Hecksher et al. [J. Chem. Phys. 142, 241103 (2015)]. We generalize these tests to include jumps ending at different temperatures. Moreover, four times larger jumps than previously are studied. The single-parameter aging tests are here for the first time applied to a hydrogen-bonded liquid. We conclude that glycerol obeys single-parameter aging to a good approximation.Comment: 20 pages, 8 figure

A systematic study of the isothermal crystallization of the mono-alcohol n-butanol monitored by dielectric spectroscopy

Isothermal crystallization of the mono-hydroxyl alcohol n-butanol was studied with dielectric spectroscopy in real time. The crystallization was carried out using two different sample cells at 15 temperatures between 120 K and 134 K. For all temperatures, a shift in relaxation times to shorter times was observed during the crystallization process, which is characterized by a drop in relaxation strength. The two different sample environments induced quite different crystallization behaviors, consistent and reproducible over all studied temperatures. An explanation for the difference was proposed on the background of an Avrami and a Maxwell-Wagner analysis. Both types analysis suggest that the morphology of the crystal growth changes at a point during the crystallization. The differences between the cells can be explained by this transition taking place at different times for the two cells

Estimating the density scaling exponent of viscous liquids from specific heat and bulk modulus data

It was recently shown by computer simulations that a large class of liquids exhibits strong correlations in their thermal fluctuations of virial and potential energy [Pedersen et al., Phys. Rev. Lett. 100, 015701 (2008)]. Among organic liquids the class of strongly correlating liquids includes van der Waals liquids, but excludes ionic and hydrogen-bonding liquids. The present note focuses on the density scaling of strongly correlating liquids, i.e., the fact their relaxation time tau at different densities rho and temperatures T collapses to a master curve according to the expression tau propto F(rho^gamma/T) [Schroder et al., arXiv:0803.2199]. We here show how to calculate the exponent gamma from bulk modulus and specific heat data, either measured as functions of frequency in the metastable liquid or extrapolated from the glass and liquid phases to a common temperature (close to the glass transition temperature). Thus an exponent defined from the response to highly nonlinear parameter changes may be determined from linear response measurements

Physical ageing studied by a device allowing for rapid thermal equilibration

Ageing of organic glasses to the equilibrium liquid state is studied by measuring the dielectric loss utilizing a microregulator where temperature is controlled by means of a Peltier element. Compared to conventional equipment the new device adds almost two orders of magnitude to the span of observable ageing times. Data for five organic glass-forming liquids are presented. The existence of an "inner clock" is confirmed by a model-free test showing that the ageing of structure is controlled by the same material time that controls the dielectric properties. At long times relaxation is not stretched, but simple exponential, and there is no "expansion gap" between the limits of the relaxation rates following up and down jumps to the same temperature

Shear and dielectric responses of propylene carbonate, tripropylene glycol, and a mixture of two secondary amides

Propylene carbonate and a mixture of two secondary amides, N-methylformamide and Nethylacetamide, are investigated by means of broadband dielectric and mechanical shear spectroscopy. The similarities between the rheological and the dielectric responses of these liquids and of the previously investigated tripropylene glycol are discussed within a simple approach that employs an electrical circuit for describing the frequency-dependent behavior of viscous materials. The circuit is equivalent to the Gemant-DiMarzio-Bishop model, but allows for a negative capacitive element. The circuit can be used to calculate the dielectric from the mechanical response and vice versa. Using a single parameter for a given system, good agreement between model calculations and experimental data is achieved for the entire relaxation spectra, including secondary relaxations and the Debye-like dielectric peak in the secondary amides. In addition, the predictions of the shoving model are confirmed for the investigated liquids