Pressure and molecular-weight dependences of elastic properties of polystyrene polymers studied by Brillouin spectroscopy

Lee, Byoung Wan; Jeong, Minseok; Choi, Jong Sun; Park, Jaehoon; Ko, Young Ho; Kim, Kwang Joo; Ko, Jae‐Hyeon

doi:10.1016/j.cap.2017.08.003

Cited by 5 publications

(1 citation statement)

References 26 publications

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“…In this manuscript, we have only performed QENS and BLS measurements on B 3 t PC. However, estimates of the BP frequency (15–18 cm –1 ) and V TA mode (1500 m/s) for PS can be readily found in the literature. The corresponding room-temperature estimate of V BP for PS is approximately 3.7 nm 3 , indicated by the blue triangle in Figure .…”

Section: Resultsmentioning

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: Resultsmentioning

confidence: 99%

Why Enhanced Subnanosecond Relaxations Are Important for Toughness in Polymer Glasses

Soles¹,

Burns²,

Itô³

et al. 2021

Macromolecules

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Flow‐induced crystallization of polylactide stereocomplex under pressure

Song

Zhao

Yang

et al. 2018

J of Applied Polymer Sci

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Although shear and pressure fields always coexist in practical polymer processing, their combined influence on the crystallization behavior of polylactide stereocomplex (SC) is ambiguous due to the limit of experiment device. In that case, a homemade device was employed to prepare samples under the coexistence of shear and pressure and explore the crystallization behavior of SC. Differential scanning calorimetry and synchrotron radiation were used to investigate the combined effect of shear flow and pressure on SC crystallization. The results show that shear flow was helpful for SC formation. Shear flow promoted the phase mixing of the polymer blends and improved the nucleation efficiency of SC. Pressure had a negative effect on SC formation because of the decrease in free volume. Regard to polylactide homogeneous (HC), pressure played a positive role on HC formation. Pressure suppressed the formation of SC network which could impede HC generation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46378.

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Acoustic properties and density of polyurea at pressure up to 13.5 GPa through Brillouin scattering spectroscopy

Ransom

Ahart

Hemley

et al. 2018

Journal of Applied Physics

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Brillouin scattering was performed on an elastomeric polyurea, an important technological polymer. Being widely used for impact modification, of particular interest is its response to extreme pressure conditions. We applied pressures up to 13.5 GPa using a diamond anvil cell and measured the longitudinal and transverse sound velocities via Brillouin light scattering. From these data, the equation of state, the elastic moduli, and Poisson's ratio were obtained. By comparison with previous dilatometry measurements up to 1 GPa, we show how viscoelastic effects can be accounted for in order to obtain an accurate equation of state. Because of the extreme strain-rate hardening of vitrifying polyurea, the property changes associated with its solidification are more subtle in the high frequency Brillouin data than observed in conventional mechanical testing and dilatometry.

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Pressure and molecular-weight dependences of elastic properties of polystyrene polymers studied by Brillouin spectroscopy

Cited by 5 publications

References 26 publications

Why Enhanced Subnanosecond Relaxations Are Important for Toughness in Polymer Glasses

Why Enhanced Subnanosecond Relaxations Are Important for Toughness in Polymer Glasses

Flow‐induced crystallization of polylactide stereocomplex under pressure

Acoustic properties and density of polyurea at pressure up to 13.5 GPa through Brillouin scattering spectroscopy

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