121 research outputs found
Two-Level Systems and Boson Peak Remain Stable in 110-Million-Year-Old Amber Glass
The two most prominent and ubiquitous features of glasses at low
temperatures, namely the presence of tunneling two-level systems and the
so-called boson peak in the reduced vibrational density of states, are shown to
persist essentially unchanged in highly stabilized glasses, contrary to what
was usually envisaged. Specifically, we have measured the specific heat of 110
million-year-old amber samples from El Soplao (Spain), both at very low
temperatures and around the glass transition Tg. In particular, the amount of
two-level systems, assessed at the lowest temperatures, was surprisingly found
to be exactly the same for the pristine hyperaged amber as for the,
subsequently, partially and fully rejuvenated samples.Comment: 22 pages, 9 figures, 2 tables (including Supplementary Material
Do tunneling states and boson peak persist or disappear in extremely stabilized glasses?
We review and concurrently discuss two recent works conducted by us, which apparently give opposite results.
Specifically, we have investigated how extreme thermal histories in glasses can affect their universal properties
at low temperatures, by studying: (i) amber, the fossilized natural resin, which is a glass which has experienced
a hyperaging process for about one hundred million years; and (ii) ultrastable thin-film glasses of
indomethacin. Specific heat Cp measurements in the temperature range 0.07 K < T < 30 K showed that the
amount of two-level systems, assessed from the linear term at the lowest temperatures, was exactly the same for
the pristine hyperaged amber glass as for the subsequently rejuvenated samples, whereas just a modest increase
of the boson-peak height (in Cp/T³) with increasing rejuvenation was observed, related to a corresponding increase
of the Debye coefficient. On the other hand, we have observed an unexpected suppression of the two-level
systems in the ultrastable glass of indomethacin, whereas conventionally prepared thin films of the same material
exhibit the usual linear term in the specific heat below 1 K ascribed to these universal two-level systems in
glasses. By comparing both highly-stable kinds of glass, we conclude that the disappearance of the tunneling
two-level systems in ultrastable thin films of indomethacin may be due to the quasi-2D and anisotropic behavior
of this glass, what could support the idea of a phonon-mediated interaction between two-level systems
Low-temperature specific heat of hyperaged and ultrastable glasses
Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 18-10-201
Ultrastable glasses : new perspectives for an old problem
Altres ajuts: the ICN2 was funded by the CERCA programme / Generalitat de Catalunya.Ultrastable glasses (mostly prepared from the vapor phase under optimized deposition conditions) represent a unique class of materials with low enthalpies and high kinetic stabilities. These highly stable and dense glasses show unique physicochemical properties, such as high thermal stability, improved mechanical properties or anomalous transitions into the supercooled liquid, offering unprecedented opportunities to understand many aspects of the glassy state. Their improved properties with respect to liquid-cooled glasses also open new prospects to their use in applications where liquid-cooled glasses failed or where not considered as usable materials. In this review article we summarize the state of the art of vapor-deposited (and other) ultrastable glasses with a focus on the mechanism of equilibration, the transformation to the liquid state and the low temperature properties. The review contains information on organic, metallic, polymeric and chalcogenide glasses and an updated list with relevant properties of all materials known today to form a stable glass
Ultrastable glasses portray similar behaviour to ordinary glasses at high pressure
Pressure experiments provide a unique opportunity to unravel new insights into glass-forming liquids by exploring its effect on the dynamics of viscous liquids and on the evolution of the glass transition temperature. Here we compare the pressure dependence of the onset of devitrification, Ton, between two molecular glasses prepared from the same material but with extremely different ambient-pressure kinetic and thermodynamic stabilities. Our data clearly reveal that, while both glasses exhibit different dTon/dP values at low pressures, they evolve towards closer calorimetric devitrification temperature and pressure dependence as pressure increases. We tentatively interpret these results from the different densities of the starting materials at room temperature and pressure. Our data shows that at the probed pressures, the relaxation time of the glass into the supercooled liquid is determined by temperature and pressure similarly to the behaviour of liquids, but using stability-dependent parametersPostprint (published version
Impact of jamming criticality on low-temperature anomalies in structural glasses
We present a novel mechanism for the anomalous behaviour of the specific heat
in low-temperature amorphous solids. The analytic solution of a mean-field
model belonging to the same universality class as high-dimensional glasses, the
spherical perceptron, suggests that there exists a crossover temperature above
which the specific heat scales linearly with temperature while below it a cubic
scaling is displayed. This relies on two crucial features of the phase diagram:
(i) The marginal stability of the free-energy landscape, which induces a
gapless phase responsible for the emergence of a power-law scaling (ii) The
vicinity of the classical jamming critical point, as the crossover temperature
gets lowered when approaching it. This scenario arises from a direct study of
the thermodynamics of the system in the quantum regime, where we show that,
contrary to crystals, the Debye approximation does not hold.Comment: 7 pages + 38 pages SI, 5 figure
Compounds found in Baltic amber and their potential medicinal uses-a URS project
This research was supported by the Undergraduate Research Scholarship (URS). Grant info: "Identification of Bioactive Compounds in Baltic Amber," University of Minnesota College of Pharmacy New Directions Grant (02/08/2016-02/07/2018
Boson peak, elasticity, and glass transition temperature in polymer glasses : Effects of the rigidity of chain bending
UTokyo FOCUS Press releases掲載「プラスチックの硬さに潜むシンプルな性質を世界で初めて明らかに。 ―高分子ガラスにおける分子振動の正体とは?― 」<研究成果> URI: https://www.u-tokyo.ac.jp/focus/ja/press/z0109_00290.htm
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