Positron Annihilation Lifetime Spectroscopy of Poly(ethylene terephthalate):  Contributions from Rigid and Mobile Amorphous Fractions

Olson, Brian G.; Lin, Jun; Nazarenko, Sergei; Jamieson, A. M.

doi:10.1021/ma034813u

Cited by 63 publications

(83 citation statements)

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“…Conceptually, it seems the dominant contribution will derive from the last source, often termed the rigid amorphous fraction, since the chains have constrained molecular mobility [Wunderlich, 2003]. Attempts have been made to probe the free-volume contributions associated with the rigid and normal or mobile amorphous fractions (RAF and MAF, respectively) [Kilburn et al, 2002;Olson et al, 2003;Dlubek et al, 2005a]. Kilburn et al [2002] carried out a PALS study of free volume in semicrystalline poly(ethylene-co-1-octene) (PO) copolymers as well as high-density polyethylene (HDPE).…”

Section: Pals As a Probe For Free Volume In Semicrystalline Polymersmentioning

confidence: 99%

“…The resulting mass fractions of the three phases, w MAF , w RAF , and X c , are plotted in Figure 12.4 as a function of the 1-octene content [Kilburn et al, 2002]. Olson et al [2003] carried out PALS studies of 22 poly(ethylene terephthalate) (PET) specimens with varying degrees of crystallinity; 11 specimens were meltcrystallized at 210 • C; and 11 were made via cold crystallization at 110 • C. Each sample was characterized thoroughly by DSC and WAXD in terms of T g , T m , and X c , and, in fact, prior to the PALS investigation, were employed in a study of oxygen permeability at room temperature, which demonstrated that the O 2 solubility in the melt-crystallized PET is higher than in the cold-crystallized PET [Lin et al, 2002]. This earlier work further established that the observed decreases in solubility and diffusion coefficient of oxygen in semicrystalline PET could be explained by the three-phase model of semicrystalline polymers, in which the RAF is considered in addition to the crystalline phase and the MAF.…”

Section: Raf (1237)mentioning

confidence: 99%

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Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

2010

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474 POSITRON ANNIHILATION LIFETIME STUDIES INTRODUCTIONThe theoretical and experimental background related to the positron annihilation lifetime spectroscopy (PALS) technique and its application as a quantitative probe for free volume in polymeric materials have been discussed extensively in Chapters 10 and 11, so we limit ourselves to a brief overview of these issues by way of introduction and commentary. Our principal focus here is to review what evidence has been generated using the PALS technique to provide insight into three topics of current interest, each of which involves probing specific heterogeneities in the amorphous polymeric phase. The first relates to the existence of concentration fluctuations in miscible polymer blends and their effect on materials properties, such as broadening of the glass transition region. The second concerns the fact that to interpret accurately the properties of certain semicrystalline polymers, such as gas transport, it is necessary to invoke a rigid amorphous phase, believed to involve the disordered chain segments that link crystalline lamellae, whose behavior differs from the usual (mobile) amorphous phase that exists far from the crystalline surface. The third topic involves evidence that a similarly rigid amorphous phase exists in polymeric nanocomposites, associated with polymer chains that lie near the surface of the inorganic particles. PALS AS A PROBE FOR FREE VOLUME IN POLYMERSA PALS experiment involves bringing a polymer sample into contact with a source of positrons, typically 22 Na. Energetic positrons emitted into the polymer by the source are slowed through collisions with atoms, creating an ionized radiation track (positron spur). In the last portion of the spur, referred to as the blob, the positron thermalizes, and either annihilates or finds a secondary electron created by the ionization to form a localized positronium atom Byakov, 2003, 2007;Stepanov et al., 2005a Stepanov et al., ,b, 2007. The spin 1 atom, called ortho-positronium (o-Ps), is three times more likely to form than is the spin 0 atom [para-positronium (p-Ps)] and is more stable than the latter, which annihilates within 125 ps. o-Ps has a long lifetime (140 ns in vacuum), which lifetime is determined by interactions with the medium. Typically, o-Ps annihilates via a pickoff mechanism, with the positron "picked off" by an electron of the medium that has opposite spin. Since o-Ps is easily polarizable, and therefore strongly repelled by the medium, it tends to localize in regions of low electron density (holes or free volume). The lifetime of o-Ps is then determined by the electron density and physical size of the hole in which it finds itself, and normally falls in the range of a few nanoseconds.Typically, therefore, a PALS spectrum consists of a minimum of three components: the short-lived p-Ps component with intensity I 1 and lifetime τ 1 = 125 ps; a free positron annihilation component, with intensity I 2 and lifetime τ 2 ; and the o-Ps component, with intensity I 3 and lifetime τ 3 . ...

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Section: Pals As a Probe For Free Volume In Semicrystalline Polymersmentioning

confidence: 99%

Section: Raf (1237)mentioning

confidence: 99%

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

2010

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“…This portion of the amorphous phase is frequently denoted as rigid amorphous fraction (RAF). [88][89][90] A strong heterogeneity in the mobility of chains in semicrystalline PDMS which is larger than the usual dynamic heterogeneity in amorphous polymers has been observed in various deuterium NMR experiments. [87,91,92] The extra heterogeneity disappears during melting.…”

Section: Size Of Holesmentioning

confidence: 99%

Temperature Dependence of Free Volume in Pure and Silica‐Filled Poly(dimethyl siloxane) from Positron Lifetime and PVT Experiments

Dlubek

Pionteck

et al. 2005

Macro Chemistry & Physics

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Summary:The microstructure of the free volume and its temperature dependence in two poly(dimethyl siloxane)s (PDMS), one in the pure state and the other filled with 35 wt.‐% of an in situ hydrophobized fumed silica with a specific surface area of 200–300 m2 · g−1, were studied by pressure‐volume‐temperature experiments (PVT, T = 22–156 °C, P = 10–200 MPa) and positron annihilation lifetime spectroscopy (PALS, T = −173–100 °C, P = 10−5 MPa). The Simha‐Somcynsky equation of state was used to estimate the hole free volume fraction, h, and free and occupied volumes, Vf = hV and Vocc = (1 − h)V, from the specific total volume, V. The PALS spectra were analyzed with the routine LT9.0, which allowed for a dispersion, σi, in all three of the lifetimes: the para‐positronium (p‐Ps, τ1), positron (e+, τ2), and ortho‐positronium (o‐Ps) lifetime (τ3). This kind of analysis delivered correct p‐Ps lifetime parameters, τ1, σ1, and I1. It was speculated that e+, like o‐Ps, undergoes Anderson localization at empty sites of the, static or dynamic, disordered structure. The hole size distribution, its mean value, 〈vh〉, and dispersion, σh, were calculated from the o‐Ps lifetimes. A comparison of 〈vh〉 with Vf was used to estimate the specific hole number, $N'_{\rm h}$. During melting of the semicrystalline samples at−38 °C (Tm), 〈vh〉 increased abruptly, and σh suddenly decreased. Both effects are explained by the disappearance of the rigid‐amorphous fraction (RAF) and, thus, a reduction in the dynamic heterogeneity. The following leveling‐off in 〈vh〉 and the low value of σh are attributed to the fast segmental relaxation in the PDMS melts which leads to a smearing of the molecule density distribution around a hole during the o‐Ps lifetime. magnified image

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“…In the determination of free volume by PALS, holes smaller than the Ps volume cannot be revealed; nevertheless, we note that such empty spaces are too small to be occupied by atoms, since the Ps volume is equal to the volume of a hydrogen atom. Therefore, as a holes probe, Ps should not suffer from a significant low threshold in the sizes of holes detected unless the number of holes undetectable by Ps is very large; in this case, these holes may provide a contribution to the free volume [McCullagh et al, 1995;Olson et al, 2003].…”

Section: Introductionmentioning

confidence: 99%

Morphology of Free‐Volume Holes in Amorphous Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Consolati

Quasso

2010

Polymer Physics

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Positron Annihilation Lifetime Spectroscopy of Poly(ethylene terephthalate): Contributions from Rigid and Mobile Amorphous Fractions

Cited by 63 publications

References 35 publications

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

Temperature Dependence of Free Volume in Pure and Silica‐Filled Poly(dimethyl siloxane) from Positron Lifetime and PVT Experiments

Morphology of Free‐Volume Holes in Amorphous Polymers by Means of Positron Annihilation Lifetime Spectroscopy

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