Molecular Orientation in Stable Glasses of Indomethacin

Dalal, Shakeel S.; Ediger, M. D.

doi:10.1021/jz3003266

Cited by 91 publications

(120 citation statements)

References 31 publications

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“…In fact, some glasses obtained by physical vapor deposition show evidence of molecular anisotropy which is partly due to the growth method of thin films from the vapor phase. In particular, ultrastable IMC glasses exhibit an extra, low-q, peak in wide-angle x-ray scattering (WAXS) spectra [44] and birrefrigence in ellipsometric measurements [45]. In our experiments [9] we have shown that the low-q peak appears indeed in the WAXS pattern of our vapor-deposited ultrastable glass, whereas it is absent in the conventionally prepared glass.…”

Section: Discussionmentioning

confidence: 57%

Do tunneling states and boson peak persist or disappear in extremely stabilized glasses?

Ramos

Pérez-Castañeda

Riobóo

et al. 2015

Low Temperature Physics

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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 C p 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 C p /T 3 ) 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.PACS: 65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.; 64.70.P-Glass transitions of specific systems; 63.50.Lm Glasses and amorphous solids; 81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging.

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Section: Discussionmentioning

confidence: 57%

Do tunneling states and boson peak persist or disappear in extremely stabilized glasses?

Ramos

Pérez-Castañeda

Riobóo

et al. 2015

Low Temperature Physics

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“…In particular, ultrastable IMC glasses exhibit an extra, low-q, peak in wide-angle X-ray scattering (WAXS) spectra (25) and birefringence in ellipsometric measurements (26). Also, computer simulations of "stable" glasses of trehalose revealed a distinct layered structure along the direction normal to the substrate that was absent in the "ordinary" glass (27).…”

Section: Resultsmentioning

confidence: 99%

Suppression of tunneling two-level systems in ultrastable glasses of indomethacin

Pérez-Castañeda

Rodríguez-Tinoco

Rodríguez‐Viejo

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

129

116

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Glasses and other noncrystalline solids exhibit thermal and acoustic properties at low temperatures anomalously different from those found in crystalline solids, and with a remarkable degree of universality. Below a few kelvin, these universal properties have been successfully interpreted using the tunneling model, which has enjoyed (almost) unanimous recognition for decades. Here we present low-temperature specific-heat measurements of ultrastable glasses of indomethacin that clearly show the disappearance of the ubiquitous linear contribution traditionally ascribed to the existence of tunneling twolevel systems (TLS). When the ultrastable thin-film sample is thermally converted into a conventional glass, the material recovers a typical amount of TLS. This remarkable suppression of the TLS found in ultrastable glasses of indomethacin is argued to be due to their particular anisotropic and layered character, which strongly influences the dynamical network and may hinder isotropic interactions among low-energy defects, rather than to the thermodynamic stabilization itself. G lasses or amorphous solids are well known (1, 2) to exhibit thermal and acoustic properties very different from those of their crystalline counterparts. Even more strikingly, many of these properties are very similar for any glass, irrespective of the type of material, chemical bonding, etc. Hence the low-temperature properties of noncrystalline solids are said to exhibit a universal "glassy behavior." In particular, below 1−2 K the specific heat of glasses depends approximately linearly on temperature, C p ∝T, and the thermal conductivity almost quadratically, κ ∝ T 2 , in clear contrast with the cubic dependences successfully predicted by Debye theory for crystals. In addition, a broad maximum in C p /T 3 [originated from the so-called "boson peak" in the reduced vibrational density of states g(ω)/ω 2 ] is also typically observed in glasses around 3−10 K, as well as a universal plateau in the thermal conductivity κ(T) in the same temperature range (1, 2).Very soon after the seminal paper by Zeller and Pohl (1) in 1971, Phillips (3) and Anderson et al. (4) independently introduced the well-known standard tunneling model (TM). The fundamental idea of the TM is the ubiquitous existence of atoms or small groups of atoms in amorphous solids due to the intrinsic atomic disorder, which can perform quantum tunneling between two configurations of very similar energy, usually named twolevel systems (TLS). This simple model was able to account for the abovementioned thermal and acoustic anomalies of glasses below 1−2 K, and soon acquired unanimous recognition. Only very few authors (5) posed then criticisms against the standard TM, pointing out how improbable it was that a random ensemble of independent tunneling states would produce essentially the same universal constant for the thermal conductivity or the acoustic attenuation in any substance. Indeed, significant discrepancies with the TM below ∼100 mK have also been reported (6-9), in particular ...

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“…31 In this context, we established in a previous work 27 that the growth front velocity of a transforming glass of IMC could not be determined considering only its limiting fictive temperature, but two different dependences arose, depending on whether the glass was deposited above or below 0.85T g . According to previous studies, 8,32,33 IMC vapour deposited glasses exhibit certain molecular anisotropy that depends on the deposition conditions. From the correlation between growth front velocity and molecular anisotropy in IMC glassy films, it was inferred that the arrangement of the molecules in the glass can also play a role in the transformation velocity.…”

Section: Introductionmentioning

confidence: 89%

The role of thermodynamic stability in the characteristics of the devitrification front of vapour-deposited glasses of toluene

Ràfols‐Ribé

González-Silveira

Rodríguez-Tinoco

et al. 2017

Phys. Chem. Chem. Phys.

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Physical vapour deposition (PVD) has settled in as an alternative method to prepare glasses with significantly enhanced properties, providing new insights into the understanding of glass transition. One of the striking properties of some PVD glasses is their transformation into liquid via a heterogeneous mechanism that initiates at surfaces/interfaces. Here, we use membrane-based fast-scanning nanocalorimetry (10 4 K s À1) to analyse the variables that govern the transformation mechanism of vapourdeposited toluene glasses with different stabilities. Thin films ranging from 20 to 250 nm were prepared at deposition temperatures between 0.70 and 1.15 times the glass transition temperature. We show how a propagating growth front is the initial transformation mechanism in all the vapour deposited samples, revealing a clear tendency to faster front velocities for less stable samples. Contrary to other glassformers such as indomethacin, toluene shows a one-to-one relationship between limiting fictive temperature and front velocity. We associate this behaviour with the much simpler molecular geometry of toluene, which would prevent the presence of strong preferential molecular arrangements in the glass. However, the propagation distance of the growth front before the homogenous transformation mechanism dominates the transition is found to be dependent on the preparation conditions rather than on the thermal stability of the glass. Understanding the link between the growth variables and the properties of PVD glasses is crucial for finding and developing potential applications of this type of glass.

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Molecular Orientation in Stable Glasses of Indomethacin

Cited by 91 publications

References 31 publications

Do tunneling states and boson peak persist or disappear in extremely stabilized glasses?

Do tunneling states and boson peak persist or disappear in extremely stabilized glasses?

Suppression of tunneling two-level systems in ultrastable glasses of indomethacin

The role of thermodynamic stability in the characteristics of the devitrification front of vapour-deposited glasses of toluene

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