Free volume changes in polyvinyl acetate measured by fluorescence spectroscopy

Meyer, Edwin F.; Jamieson, A. M.; Simha, Robert; Palmen, J. H. M.; Booij, H. C.; Maurer, Frans H.J.

doi:10.1016/0032-3861(90)90113-d

Cited by 56 publications

(28 citation statements)

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“…Particularly, it is worth noting that the behavior of this aging process can be expressed by a master curve as illustrated in Figure 7 where the strain " normalized to its maximum " max was plotted versus the non-dimensionalized elapse time defined as ðt e Â k a Þ. Here, t e is the elapse time in the experiment and k a is the rate constant of the aging process obtained by fitting the data to eq (9). These results clearly indicate that the aging kinetics of PEA can be expressed by a master curve.…”

Section: Kinetics Of Physical Aging Observed By Mach-zehnder Interfermentioning

confidence: 99%

“…[6][7][8] Recently, fluorescence method using probe molecules with the internal rotations sensitive to viscosity was also utilized to examine the aging phenomena of polymers. 9 Furthermore, an X-ray diffraction method was recently proposed for monitoring the strain distribution in amorphous materials, 10 which would be able to provide a potential tool for studies on physical aging.…”

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Physical Aging of Photo-Crosslinked Poly(ethyl acrylate) Observed in the Nanometer Scales by Mach-Zehnder Interferometry

et al. 2009

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Deformation in the nanometer scales of photo-crosslinked poly(ethyl acrylate) (PEA) was in situ monitored by MachZehnder interferometry (MZI). Upon irradiation with 365 nm, anthracene labeled on the PEA chains undergoes photodimerization, generating the PEA networks. The cross-link kinetics induced by different light intensities was monitored by using a UV-visible spectrometer. On the other hand, the deformation in the nanometer scales of the photocross-linked polymer was measured in situ by using a Mach-Zehnder interferometer (MZI) under the same experimental conditions. The aging data observed by ceasing irradiation at different stages of the photocuring process reveal a general relationship for the kinetics of aging under different cross-link densities. Upon approaching the glassy region, mobility of polymer quickly decreases and eventually almost vanishes as the polymer is vitrified. This phenomenon is often observed in polymers under cooling, thermally curing or photocuring. A number of interesting physical phenomena such as the Kohlrausch-Williams-Watts (KWW) relaxation behavior 1,2 have been observed in the vicinity of this vitrification process. For this particular case, diffusion becomes size-dependent and the kinetics is no longer expressible by a simple exponential function of time.3 As the cross-link reaction proceeds to a certain point, the polymer enters the glassy state and falls out of equilibrium, exhibiting the so-called physical aging phenomena whose time-evolution is much slower than the time scales of observation.4 It is well known that photochemical reactions in the bulk state of polymers often proceed non-uniformly due to the inhomogeneity of the local environments.5 This inhomogeneous reaction kinetics, particularly for the case of cross-link, could generate a local transient strain field in these reacting polymers. Depending upon the relative distance from the glass transition temperature (T g ), this local strain field can either completely relax or persist for a long time inside the sample during the course of the reaction. The latter case would be enhanced by the glassy state where the relaxation of the reaction-induced strain becomes extremely slow.Physical aging of polymer has been extensively investigated by a number of experimental methods. Among them, dilatometry has been widely used to monitor the changes in volume of polymers at different temperatures in the glassy state. [6][7][8] Recently, fluorescence method using probe molecules with the internal rotations sensitive to viscosity was also utilized to examine the aging phenomena of polymers.9 Furthermore, an X-ray diffraction method was recently proposed for monitoring the strain distribution in amorphous materials, 10 which would be able to provide a potential tool for studies on physical aging.Recently, we have developed a Mach-Zehnder interferometer (MZI) equipped with a high-pressure Mercury lamp (350 W, Moritex, Japan) to in situ monitor the time-evolution process of the strain in photoreactive polymers.11 In this study,...

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Section: Kinetics Of Physical Aging Observed By Mach-zehnder Interfermentioning

confidence: 99%

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confidence: 99%

Physical Aging of Photo-Crosslinked Poly(ethyl acrylate) Observed in the Nanometer Scales by Mach-Zehnder Interferometry

et al. 2009

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“…The free volume concept has been extensively used to interpret various macroscopic physical properties 1 -7 of polymers such as viscosity, elasticity, glass transition, and structural relaxation, all of which are important from the view point of controlling mechanical properties of polymers, The data obtained by such microscopic techniques as fluorescence, 8 photochemical hole burning,9 and nuclear magnetic resonance 10 are often discussed in relation to the predictions of the free volume theory. Another empirical technique, which can sensitively probe the local structure of the polymers, is positron annihilation.…”

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Positronium Diffusion in Polystyrene at Low Temperatures

Ito

Ujihira

1998

Polym J

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ABSTRACT:Diffusion of ortho-positronium (o-Ps) in polystyrene (PS) at low temperatures (20-300 K) was studied by means of the positron annihilation lifetime technique. 2,2'-Dinitrobiphenyl was added to PS as a Ps quencher, and the diffusion coefficients were determined from the measured Ps quenching rate constants, assuming that the reaction between Ps and the quencher is entirely diffusion-controlled. The determined diffusion coefficient increases with increasing temperature, and is significantly influenced by such structural relaxation of PS as i5 and fl transitions. The estimated diffusion length of o-Ps, 1.5-2.5 nm, is only a few times larger than the Ps cavity size, indicating that the effect of the Ps diffusion on the Ps lifetime distribution is almost insignificant in PS at low temperatures. The size distributions of free volume in pure PS were obtained from the lifetime distributions of o-Ps without taking an effect of the diffusivity of o-Ps into consideration. Peculiar broadening of the size distribution of free volume for PS, which is induced by an inhomogeneous local structure, is observed at the transition temperatures, T0 and Tp. KEY WORDSPolystyrene/ Diffusion Coefficient/ Free Volume/ Positronium / Positron Annihilation / Structural Relaxation / The free volume concept has been extensively used to interpret various macroscopic physical properties 1 -7 of polymers such as viscosity, elasticity, glass transition, and structural relaxation, all of which are important from the view point of controlling mechanical properties of polymers, The data obtained by such microscopic techniques as fluorescence, 8 photochemical hole burning,9 and nuclear magnetic resonance 10 are often discussed in relation to the predictions of the free volume theory. Another empirical technique, which can sensitively probe the local structure of the polymers, is positron annihilation.The observed decay curve of positrons annihilating in a polymer contains a long-lived component with an average lifetime of 1-5 ns. The component is attributed to "pick-off" annihilation of ortho-positronium (o-Ps: the spin-parallel bound state between a positron and an electron) localized in a sub-nanometer size hole. A relation between the pick-off annihilation lifetime and the cavity size was derived based on a simple quantum mechanical model initially proposed by Tao 11 and later developed by Eldrup et al.,12 and Nakanishi et al. 13 • 14 Several empirical correlations between the average Ps cavity size estimated from the relation and free volume properties of polymers were reported. 15 · 16 In addition to this, attempts have been made to deduce the size distribution of the Ps cavity by inverse Laplace transformation of the positron lifetime data. This paper concerns diffusion of Ps in a polymer at low temperatures. Following Hirata et al. 1 7 and Kobayashi et al., 18 2,2' -dinitrobiphenyl (DNB) was added to polystyrene (PS) as a Ps quencher, and the diffusion coefficients were determined from the measured Ps quenching rate constants, assum...

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“…In addition to PALS, other spectroscopic techniques that have been used to inves tigate physical aging are electron spin resonance spectroscopy (ESR) [83], fluores cence spectroscopy [84][85][86], dielectric spectroscopy [87], and Fourier-transform infrared spectroscopy (FTIR) [88].…”

Section: Other Spectroscopic Techniquesmentioning

confidence: 99%

Physical Aging of Polymer Blends

Cowie

Arrighi

2010

Encyclopedia of Polymer Blends

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Introduction to Physical AgingWhen a polymeric material is processed, fabricated, and placed in its working environment it cannot be regarded, automatically, as being stable, as it is subject to a wide range of possible changes, collectively known as aging processes. The polymer can react with its environment (light, oxygen, water, etc.) and undergo several non-reversible chemical reactions. These lead to changes in the polymer structure such as chain scission, oxidation, decarboxylation, hydrolysis, dehalogena tion, crosslinking, and so on, leading to degeneration of the polymer physical properties, for example, discoloration, brittleness, or loss of tensile strength. This type of aging will not be considered here.More subtle changes can also take place that do not involve chemical modification. These are a consequence of small-scale relaxation events that take place predomi nantly in the amorphous regions of glassy polymers, at temperatures below the glass transition temperature, g . The resulting effects are referred to as physical aging and, unlike chemical aging, are reversible.In physical aging the chemical structure of the polymer chain remains unchanged but the local packing of the chains alters over a period of time, leading to changes in the bulk properties of the material [1].When an amorphous, or semi-amorphous, polymer is quenched from the melt to a temperature a , below g , there is insufficient time for the chains to relax fully to their lowest energy configurations and a vitreous state is formed that is not in equilibrium with its surroundings. Such a state will have an excess enthalpy, entropy, and volume, and if the material is held at that temperature it will attempt to move towards a state of thermodynamic equilibrium by losing those excess quantities over a period of time. This is achieved through a series of localized molecular relaxation processes that is termed physical aging and is manifest as the time dependent alteration in polymer properties (density, modulus, compliance, g , material dimensions, and fracture toughness) at zero stress and constant temperature. Clearly, such changes will have an impact on the use and long-term stability of materials like high-performance thermoplastics and composites that are manufactured using techniques involving Edited by Avraam I. Isayev

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Free volume changes in polyvinyl acetate measured by fluorescence spectroscopy

Cited by 56 publications

References 20 publications

Physical Aging of Photo-Crosslinked Poly(ethyl acrylate) Observed in the Nanometer Scales by Mach-Zehnder Interferometry

Physical Aging of Photo-Crosslinked Poly(ethyl acrylate) Observed in the Nanometer Scales by Mach-Zehnder Interferometry

Positronium Diffusion in Polystyrene at Low Temperatures

Physical Aging of Polymer Blends

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