Communication: Effect of density on the physical aging of pressure-densified polymethylmethacrylate

Casalini, R.; Roland, C. M.

doi:10.1063/1.4995567

Cited by 13 publications

(29 citation statements)

References 33 publications

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“…5,[10][11][12] A recent paper reported that the change in the JG b-relaxation time and dielectric strength during physical aging of two PMMA glasses formed at 188 MPa and at 0.1 MPa are the same. 13 Thus, the change of the secondary relaxation with aging is found to be independent of the density, since the glass formed at high pressure of 188 MPa is denser than that formed at 0.1 MPa. To rationalize this observation, the authors of ref.…”

Section: Introductionmentioning

confidence: 91%

“…To rationalize this observation, the authors of ref. 13 suggested that the average density does not govern the dynamics of the glass, but rather the local structure and barriers for thermal fluctuations of density are the main control parameters. All these complicated and uneven observed changes of the secondary relaxation on aging make them inappropriate to distinguish secondary relaxation having connection to the a-relaxation or not.…”

Section: Introductionmentioning

confidence: 99%

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Distinguishing different classes of secondary relaxations from vapour deposited ultrastable glasses

Rodríguez-Tinoco

Ngai

Rams-Baron

et al. 2018

Phys. Chem. Chem. Phys.

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Secondary relaxations persistent in the glassy state after structural arrest are especially relevant for the properties of the glass. A major thrust in research in dynamics of glass-forming liquids is to identify what secondary relaxations exhibit a connection to the structural relaxation and are hence more relevant. Via the Coupling Model, secondary relaxations having such connection have been identified by properties similar to the primitive relaxation of the Coupling Model and are called the Johari-Goldstein (JG) β-relaxations. They involve the motion of the entire molecule and act as the precursor of the structural α-relaxation. The change in dynamics of the secondary relaxation by aging an ordinary glass is one way to understand the connection between the two relaxations, but the results are often equivocal. Ultrastable glasses, formed by physical vapour deposition, exhibit density and enthalpy levels comparable to ordinary glasses aged for thousands of years, as well as some particular molecular arrangement. Thus, ultrastable glasses enable the monitoring of the evolution of secondary processes in case aging does not provide any definitive information. Here, we study the secondary relaxation of several ultrastable glasses to identify different types of secondary relaxations from their different relationship with the structural relaxation. We show the existence of two clearly differentiated groups of relaxations: those becoming slower in the ultrastable state and those becoming faster, with respect to the ordinary unaged glass. We propose ultrastability as a way to distinguish between secondary processes arising from the particular microstructure of the system and those connected in properties to and acting as the precursor of the structural relaxation in the sense of the Coupling Model.

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Distinguishing different classes of secondary relaxations from vapour deposited ultrastable glasses

Rodríguez-Tinoco

Ngai

Rams-Baron

et al. 2018

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

show abstract

“…42 After a comprehensive discussion it was concluded that in these cases the average density does not govern the properties of the glass, but rather the local structure and barriers for thermal fluctuations of density are the main control parameters. 38 We suggest that elastically altered states of glasses would show difference in the strength and dynamics of the JG relaxation. But no such relaxation has been known to occur in sc-C60 or C60-OG.…”

Section: B Thermal Conductivity Features On Cooling and Kinetic Freementioning

confidence: 83%

“…Both features are expected on the phenomenological basis of glass formation. 68 Also, recent dilatometric studies by Casalini and Roland 38 have found that the sub-Tg feature has moved so close to Tg that it is observed as a low-temperature broadening of the Tg. It is possible that our findings indicate a shift so large that the sub-Tog feature became undiscernible.…”

Section: B Thermal Conductivity Features On Cooling and Kinetic Freementioning

confidence: 98%

“…34 It is now of interest for investigating the elastic modulus, 35 the source of the JG relaxation, and of other features of the glassy state. 36,37,38,39 A recent paper 40 formally described the excess free energy of elastically expanded glasses and related it to increase in the solubility of a glass in a given solvent. As mentioned earlier here, in contrast to glasses and the OGs made from other ODICs, orientational disorder of C60 molecules in sc-C60…”

Section: Orientations Rp (= [P]/([h]+[p]mentioning

confidence: 99%

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Instability and thermal conductivity of pressure-densified and elastically altered orientational glass of Buckminsterfullerene

Johari

Andersson

Sundqvist

2018

The Journal of Chemical Physics

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We report on the temperature, pressure, and time (T, p, and t)-dependent features of thermal conductivity, κ, of partially ordered, non-equilibrium state of C60-OG, the orientational glass of Buckminsterfullerene (at T below the orientational freezing temperature Tog) made more unstable (i) by partially depressurizing its high-p formed state to elastically expand it and (ii) by further pressurizing that state to elastically contract it. The sub-Tog effects observed on heating of C60-OG differ from those of glasses because phonon propagation depends on the ratio of two well-defined orientational states of C60 molecules and the density of the solid. A broad peak-like feature appears at T near Tog in the κ-T plots of C60-OG formed at 0.7 GPa, depressurized to 0.2 GPa and heated at 0.2 GPa, which we attribute to partial overlap of the sub-Tog and Tog features. A sub-Tog local minimum appears in the κ-T plots at T well below Tog of C60-OG formed at 0.1 GPa, pressurized to 0.5 GPa and heated at 0.5 GPa and it corresponds to the state of maximum disorder. Although Buckminsterfullerene is regarded as an orientationally disordered crystal, variation of its properties with T and p is qualitatively different from other such crystals. We discuss the findings in terms of the nature of its disorder, sensitivity of its rotational dynamics to temperature, and the absence of the Johari-Goldstein relaxation. All seem to affect the phenomenology of its glass-like transition.

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Main α relaxation and slow β relaxation processes in a La30Ce30Al15Co25 metallic glass

Qiao

Chen

Casalini

et al. 2019

Journal of Materials Science & Technology

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Communication: Effect of density on the physical aging of pressure-densified polymethylmethacrylate

Cited by 13 publications

References 33 publications

Distinguishing different classes of secondary relaxations from vapour deposited ultrastable glasses

Distinguishing different classes of secondary relaxations from vapour deposited ultrastable glasses

Instability and thermal conductivity of pressure-densified and elastically altered orientational glass of Buckminsterfullerene

Main α relaxation and slow β relaxation processes in a La30Ce30Al15Co25 metallic glass

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