Physical aging of atactic polystyrene as seen by dielectric relaxational and low-frequency vibrational Raman spectroscopies

Wypych, Aleksandra; Duval, E.; Boiteux, Gisèle; Ulański, Jacek; David, Laurent; Seytre, Gérard; Mermet, A.; Stevenson, Isabelle; Kozanecki, Marcin; Okrasa, Lidia

doi:10.1016/j.jnoncrysol.2005.04.077

Cited by 15 publications

(15 citation statements)

References 21 publications

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“…6, 14, and 15͒ and originates from the hindered rotation of phenyl groups around the C-C bond with the backbone. E a,II exceeds by about 4 kcal/ mol the experimentally 15,16 and theoretically 17,18 determined activation energy E ␤ of 17-18 kcal/ mol for the ␤-relaxation in PS. Despite this discrepancy, which will be discussed in greater detail below, these results elucidate the increase in the friction coefficient from I to II by a transition between two distinctly different dissipation mechanisms of molecular origin.…”

Section: Resultsmentioning

confidence: 78%

“…3͑a͒ reveals a relaxation peak velocity v R of 0.8 m / s. As both IFA and DRS are sensitive to the same relaxation phenomena, relaxation peak frequencies from DRS loss curves can be employed. Thus, DRS frequency data by Wypych et al, 16 i.e., f R = 100 Hz at T R = T ␤ = 263 K, E a = 17.0 kcal/ mol yields for the ␤-relaxation of PS an entropic contribution T R ⌬S ␤ of 4.5 kcal/ mol. This result is in accordance with the excess energy determined above, E a,II − E ␤ .…”

Section: Resultsmentioning

confidence: 89%

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Cooperative and submolecular dissipation mechanisms of sliding friction in complex organic systems

Knorr

Gray

Overney

2008

The Journal of Chemical Physics

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Energy dissipation in single asperity sliding friction was directly linked to submolecular modes of mobility by intrinsic friction analysis, involving time-temperature superposition along with thermodynamic stress and reaction rate models. Thereby, polystyrene served as a representative tribological sample for organic and amorphous complex systems. This study reveals the significance of surface and subsurface (alpha-, beta-, and gamma-) relaxational modes, which couple under appropriate external conditions (load, temperature, and rate) with shear induced disturbances, and thus gives rise to material specific frictional dissipation. At low pressures and temperatures below the glass transition point, the phenyl pendant side groups of polystyrene, known for their preferential orientation at the free surface, were noticed to be the primary channel for dissipation of kinetic sliding-energy. While this process was found to be truly enthalpic (activation energy of 8 kcalmol), energy dissipation was shown to possess both enthalpic and cooperative entropic contributions above the loading capacity of the surface phenyl groups (9.9 kcalmol) or above the glass transition. Apparent Arrhenius activation energies of frictional dissipation of 22 and 90 kcalmol, respectively, and cooperative contributions up to 80% were found. As such, this study highlights issues critical to organic lubricant design, i.e., the intrinsic enthalpic activation barriers of mobile linker groups, the evaluation of cooperative mobility phenomena, and critical tribological parameters to access or avoid coupling between shear disturbances and molecular actuators.

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Section: Resultsmentioning

confidence: 78%

Section: Resultsmentioning

confidence: 89%

Cooperative and submolecular dissipation mechanisms of sliding friction in complex organic systems

Knorr

Gray

Overney

2008

The Journal of Chemical Physics

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“…According to the nano-heterogeneity cohesion model, the decrease of Boson peak in LFRS spectra after aging is attributed to smoothing of the elastic constant contrast at the nanometric scale. The softer zones are believed to become more cohesive after aging, i.e., their elastic constants increase and become close to those inside the nanodomains [14,18,23]. The plot in inset in Fig.…”

Section: Discussionmentioning

confidence: 97%

“…It is due to fast relaxational motions which have a relaxation time in a picosecond range. Since polycarbonate [31], polystyrene [23], PBzMA and its copolymers have common structural element and all exhibit very strong QELS in LFRS at 293 K, the origin of QELS can be connected with fast motions of phenyl groups. Kawaguchi et al, using neutron scattering methods, have confirmed that in atactic polystyrene QELS is due to fast relaxations of the phenyl side rings [32].…”

Section: Discussionmentioning

confidence: 99%

“…In spite of its established influence on macroscopic thermodynamic and molecular mobility parameters in polymers [20][21][22], physical ageing also concerns the polymer structure at the nanometric level [13,14,23]. In case of amorphous homopolymers, aging leads to a more homogeneous structure in term of elasticity constants at a scale of few nanometers [14,18,23], while for the amphiphilic random copolymers, like a copolymers poly(MMA/BzMA), this effect is not established because of the presence of a pre-existing structural heterogeneity. The results obtained from LFRS were analyzed in a frame of the model of heterogeneous nanostructure of glasses proposed by Duval et al [24].…”

Section: Introductionmentioning

confidence: 99%

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Structural changes on nanometric level in copolymers of methyl methacrylate with benzyl methacrylate as investigated by low frequency Raman scattering and small angle X-ray scattering

Wypych¹,

Duval²,

Boiteux³

et al. 2006

Journal of Non-Crystalline Solids

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Polystyrene/calcium phosphate nanocomposites: Morphology, mechanical, and dielectric properties

Selvin

Thomas

Zafeiropoulos

et al. 2011

Polymer Engineering & Sci

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Matrix mediated synthesis of nanoparticles was utilized to prepare calcium phosphate nanoparticles with a size of 10 nm. The particles were characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Nanocomposites of polystyrene and nano‐calcium phosphate were prepared by the melt‐mixing technique. The composites were characterized by TEM to assess the dispersion of the nanoparticles. SAXS measurements of the composites and the fit with Beaucage model described the fractal dimensions of the particles. Mechanical properties of the composites significantly improved with the addition of nanofillers. Dielectric behavior of the nanocomposites was measured with respect to the filler content, temperature, and frequency. The dielectric constant increases with increase in temperature and decreases with increase in frequencies. Dielectric constant increased with filler content in all frequencies; however, lower frequencies showed marked effect. α‐Relaxation of the composites from the dissipation factor of the composites showed higher values for the lower frequencies. Electrical conductivity increased with respect to the filler content and volume resistivity showed the reverse trend. The theoretical prediction of the dielectric constant showed close agreement with the experimental value. POLYM. ENG. SCI. 2012. © 2011 Society of Plastics Engineers

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Physical aging of atactic polystyrene as seen by dielectric relaxational and low-frequency vibrational Raman spectroscopies

Cited by 15 publications

References 21 publications

Cooperative and submolecular dissipation mechanisms of sliding friction in complex organic systems

Cooperative and submolecular dissipation mechanisms of sliding friction in complex organic systems

Structural changes on nanometric level in copolymers of methyl methacrylate with benzyl methacrylate as investigated by low frequency Raman scattering and small angle X-ray scattering

Polystyrene/calcium phosphate nanocomposites: Morphology, mechanical, and dielectric properties

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