Molecular motions in glassy polycarbonate below its glass transition temperature

Arrese-Igor, Silvia; Mitxelena, Olatz; Arbe, Arantxa; Alegría, Ángel; Colmenero, Juan; Frick, B.

doi:10.1016/j.jnoncrysol.2006.02.168

Cited by 8 publications

(5 citation statements)

References 6 publications

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“…QENS measurements by Arrese-Igor and co-workers highlight the complexity of the motions in glassy PCs. They reported that the phenyl rings undergo a multitude of motions that can be described as oscillations, rotations, and flips, which are then coupled to both the methyl group rotations and carbonate group motions. − These motions are all coupled and complicated. Conversely, freely rotating methyl groups, such as those on the phenyl rings of tetramethyl bisphenol-A polycarbonate, do not contribute to toughness.…”

Section: Discussionmentioning

confidence: 99%

Why Enhanced Subnanosecond Relaxations Are Important for Toughness in Polymer Glasses

Soles¹,

Burns²,

Itô³

et al. 2021

Macromolecules

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This manuscript explores the connection between the fast relaxation processes in an undeformed polymer glass and essential trends in the mechanical toughness, a nonlinear mechanical property that is of practical interest for engineering polymers with high impact strength. We quantify the time scale of the molecular relaxations in the subnanosecond regime for a quiescent polycarbonate glass using inelastic and quasi-elastic neutron scattering and then correlate these processes with the macroscopic brittle-to-ductile transition (BDT), which demarcates a change in the dominant mechanism of failure and a marked increase in the material toughness. We show that the macroscopic phenomenon of the BDT corresponds to a change in the dominant dynamical process at the nanoscale. The brittle regime is characterized by collective vibrational modes (the so-called Boson peak) with a characteristic time scale τ ≈ 0.5–0.8 ps, while slower collective relaxations with τ ≈ 3 ps become dominant above the BDT. We further establish that the onset of ductility coincides with the appearance of anharmonicity in the mean-square atomic displacement ⟨u 2⟩ on a picosecond time scale, emphasizing that fast anharmonic molecular motions are important for energy dissipation. This builds upon our previous report correlating toughness with the amplitude of these anharmonic fluctuations across a wide range of polycarbonate glasses. Brillouin light scattering measurements are used to characterize the bulk and shear moduli of the material, revealing a concomitant upturn in Poisson’s ratio in the region of the BDT, a phenomenon that has been reported in metallic and oxide glasses. The ratio of transverse acoustic mode velocity and the Boson peak frequency is used to estimate the length scale for these processes, indicating that the dynamic heterogeneities are collective across 100–1000s of atoms. These length scales are strikingly similar to the activation volume of yield derived from mechanical measurements, suggesting that these fast and collective relaxation processes may be related to the mechanisms of yield.

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Section: Discussionmentioning

confidence: 99%

Why Enhanced Subnanosecond Relaxations Are Important for Toughness in Polymer Glasses

Soles¹,

Burns²,

Itô³

et al. 2021

Macromolecules

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“…Dashed lines in Figure show in detail the effect of orientation on the two components at 200 K. Furthermore, according to our results, the reduction factor hardly depends on temperature, and it is about a 14% (dashed−dotted line in Figure ) reduction for component I and as high as a 35% reduction for component II (dashed line in Figure ). It is also noteworthy that these estimates allow also to account for the measurable effect of chain orientation on the phenylene dynamics as determined by QENS …”

Section: Discussionmentioning

confidence: 99%

On the Molecular Motions Originating from the Dielectric γ-Relaxation of Bisphenol-A Polycarbonate

2006

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We have investigated the molecular motions responsible for the dielectric γ-relaxation of bisphenol A polycarbonate (BPA-PC) by taking advantage of the unbalanced influence of cold-drawing in the dielectric losses. The direct comparison of the dielectric relaxation curves measured on the BPA-PC samples uniaxially stretched below the glass transition temperature with those corresponding to the nonstretched samples allowed us to resolved two main components of the dielectric γ-relaxation. The characteristic times of each of these components nearly coincide with those derived by neutron scattering and deuterium nuclear magnetic resonance for two welldefined jumps of the phenylene rings, evidencing the cooperativity among the motions of the different molecular groups forming the polycarbonate repeating unit. A more detailed analysis of the orientation effects on the dielectric γ-relaxation reveals a weaker third component with characteristic time scales close to those reported in the literature for the fast phenylene ring oscillations. On the basis of these three components we have been able to accurately describe the relaxation behavior of both oriented and nonoriented samples over an extremely wide temperature interval (50-350 K). From these results, we conclude that the low temperature dielectric behavior is mainly driven by the phenylene π-flips, but at temperatures above 200 K, the dielectric relaxation becomes increasingly governed by the concurrent rotation of the carbonate/phenylene units, being these motions those more strongly hindered by chain orientation. Some implications of these finding on the mechanical properties of polycarbonate are discussed.

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“…However, within this range of temperatures, neutron scattering and dielectric spectroscopy show that molecular motions with the characteristic time of 10 −10 to 10 −9 s increase systematically from zero at T β to a high plateau at T g . The vibrations of different molecular groups are coupled (e.g., rotation of the phenyl rings is related to motion of the carbonate and methyl groups) [Arrese-Igor et al, 2006].…”

Section: Glassy State and Physical Agingmentioning

confidence: 99%

Equations of State and Free‐Volume Content

Moulinié

Utracki

2010

Polymer Physics

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Molecular motions in glassy polycarbonate below its glass transition temperature

Cited by 8 publications

References 6 publications

Why Enhanced Subnanosecond Relaxations Are Important for Toughness in Polymer Glasses

Why Enhanced Subnanosecond Relaxations Are Important for Toughness in Polymer Glasses

On the Molecular Motions Originating from the Dielectric γ-Relaxation of Bisphenol-A Polycarbonate

Equations of State and Free‐Volume Content

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