Physical aging behavior of the normal force and torque in polymer glasses

Flory, Anny; McKenna, Gregory B.

doi:10.1007/s11043-010-9114-9

Cited by 13 publications

(10 citation statements)

References 10 publications

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“…will vary as a function of the strain at which stress relaxation is initiated, even though the average segmental relaxation time is not changing; this dependence on strain is discussed below. Related considerations in the determination of a mechanical relaxation time have been discussed previously …”

Section: Methodsmentioning

confidence: 99%

Comparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass

Bending

Ediger

2016

J Polym Sci B Polym Phys

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We performed constant strain rate deformation and stress relaxation on a poly(methyl methacrylate) glass at Tg – 19 K, utilizing three strain rates and initiating the stress relaxation over a large range of strain values. Following previous workers, we interpret the initial rate of decay of the stress during the relaxation experiment as a purely mechanical measure of mobility for the system. In our experiments, the mechanical mobility obtained in this manner changes by less than a factor of 3 prior to yield. During these mechanical experiments, we also performed an optical measurement of segmental mobility based on the reorientation of a molecular probe; we observe that the probe mobility increases up to a factor of 100 prior to yield. In the post‐yield regime, in contrast, the mobilities determined mechanically and by probe reorientation are quite similar and show a similar dependence on the strain rate. Dynamic heterogeneity is found to initially decrease during constant strain rate deformation and then remain constant in the post‐yield regime. These combined observations of mechanical mobility, probe mobility, and dynamic heterogeneity present a challenge for theoretical modeling of polymer glass deformation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1957–1967

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Section: Methodsmentioning

confidence: 99%

Comparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass

Bending

Ediger

2016

J Polym Sci B Polym Phys

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“…In and other references, various authors have discussed and proposed several step rate corrections, but the more or less unanimous conclusion was that the effect was only important in materials with significant contribution of relaxation times similar to (or shorter than) the ramp time. In addition, relative errors affecting the relaxation modulus,

E_{r} true(t true)

, were generally small, though the same would not necessarily apply to best‐fit KWW parameters, given their extreme sensitivity to only slight changes in the data.…”

Section: Resultsmentioning

confidence: 99%

Toward the accurate modeling of amorphous nonlinear materials—polymer stress relaxation (I)

Pinto

André

2016

Polymer Engineering & Sci

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We expand our analytical modeling strategy for polymer non-linear stress relaxation (A) to specify the remaining steps to accurately deal with the nonaffine nature of the materials' local strains and stresses relative to their average overall values, and (B) to make it consistent with a new cooperative theory of amorphous materials dynamics, providing a model of tunable fragility that sheds light to most aspects of the behavior, including the glass transition. The stress relaxation models (1) describe a nonlinear (straindependent) behavior that becomes linear at very low strains, (2) quantify the effect of temperature, (3) may quantify the effects of changes in free volume, and (4) ensure very fast computations of the materials' response irrespective of the experimental time scale. The models are sensitive to the influence of different initial states of the material, as may result from varying degrees of molecular orientation and aging levels, and are able to predict from experimental stress relaxation moduli (for a poly (methylmethacrylate)-PMMA and a bis-phenol-A polycarbonate-PC) the values of the crossover frequency, m c , crossover temperature, T c , and the minimum activation energy, in addition to the initial and long-time plateau moduli, in agreement with independently measured values. POLYM.ENG. SCI., 56:348-360,

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“…The relaxation time t r included a correction for the loading time t l following the Zapas–Craft approach: t r = t − t l /2, where t is the time with origin t = 0 at the onset of loading. This correction enabled accounting for the relaxation, which occurred during loading . Tests were carried out both at 30 °C (10, 40, 50, 60, 70, 80, and 90% RH) and at 50 °C (50 and 90% RH).…”

Section: Methodsmentioning

confidence: 99%

Viscoelastic phase diagram of fluorinated and grafted polymer films and proton‐exchange membranes for fuel cell applications

Leterrier

Thivolle

Oliveira

et al. 2013

J Polym Sci B Polym Phys

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The influence of temperature and moisture activity on the viscoelastic behavior of fluorinated membranes for fuel cell applications was investigated. Uncrosslinked and crosslinked ethylene tetrafluoroethylene (ETFE)-based proton-conducting membranes were prepared by radiation grafting and subsequent sulfonation and their behavior was compared with ETFE base film and commercial Nafion V R NR212 membrane. Uniaxial tensile tests and stress relaxation tests at controlled temperature and relative humidity (RH) were carried out at 30 and 50 C for 10% < RH < 90%. Grafted films were stiffer and exhibited stronger strain hardening when compared with ETFE. Similarly, both uncrosslinked and crosslinked membranes were stiffer and stronger than Nafion V R . Yield stress was found to decrease and moisture sensitivity to increase on sulfonation. The viscoelastic relaxation of the grafted films was found to obey a power-law behavior with exponent equal to 20.04 6 0.01, a factor of almost 2 lower than ETFE, weakly influenced by moisture and temperature. Moreover, the grafted films presented a higher hygrothermal stability when compared with their membranes counterparts. In the case of membranes, a power-law behavior at RH < 60% was also observed. However, a markedly different behavior was evident at RH > 60%, with an almost single relaxation time exponential. An exponential decrease of relaxation time with RH from 60 s to 10 s was obtained at RH 70% and 30 C. The general behavior of grafted films observed at 30 C was also obtained at 50 C. However, an anomalous result was noticed for the membranes, with a higher modulus at 50 C when compared with 30 C. This behavior was explained by solvation of the sulfonic acid groups by water absorption creating hydrogen bonding within the clusters. A viscoelastic phase diagram was elaborated to map critical conditions (temperature and RH) for transitions in time-dependent behavior, from power-law scaling to exponential scaling.

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Physical aging behavior of the normal force and torque in polymer glasses

Cited by 13 publications

References 10 publications

Comparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass

Comparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass

Toward the accurate modeling of amorphous nonlinear materials—polymer stress relaxation (I)

Viscoelastic phase diagram of fluorinated and grafted polymer films and proton‐exchange membranes for fuel cell applications

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