The free volume in two untreated, pressure-densified, and CO2 gas exposed polymers from positron lifetime and pressure-volume-temperature experiments

Dlubek, G.; Pionteck, Jürgen; Shaikh, Muhamad Qasim; Häußler, Liane; Thränert, Stefan; Hassan, E.M.; Krause‐Rehberg, R.

doi:10.1515/epoly.2007.7.1.1244

Cited by 17 publications

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“…As an example, Figure 11.9 shows the thermal expansion of the specific total volume V of polycarbonate (PC) at ambient pressure from PVT experiments using a fully automated Gnomix high-pressure (mercury) dilatometer [Dlubek et al, 2007d]. With the help of the S-S equation of state, the specific occupied volume, V occ = yV = (1 − h)V and the specific hole free volume, V fh = hV = V − V occ , were estimated.…”

Section: Comparison Of Pals Results With Those From the Simha-somcynsmentioning

confidence: 99%

“…Open symbols, experimental data; dots, S-S equation of state fits to the volume in the temperature range T > T g ; stars, free volume calculated from V f = N h v h , where v h is the mean hole volume from PALS and N h is the specific hole density, assumed to be constant at N h = 0.67 × 10 21 g −1 (corresponding to 0.81 nm −3 at 300 K). (Adapted from Dlubek et al, [2007d].) 1.…”

Section: Comparison Of Pals Results With Those From the Simha-somcynsmentioning

confidence: 99%

“…The opposite effect usually occurs when exposing a polymer glass to a gas atmosphere at high pressure [Hong et al, 1996]. We have studied the change in the free volume as a consequence of these treatments for COP and PC [Dlubek et al, 2007d]. Figure 11.13 shows the results of our study for COP plotting V f from the S-S equation-of-state analysis of PVT experiments, and v h and σ h from PALS , and CO 2 gas-exposed and degassed (diamonds).…”

Section: Comparison Of Pals Results With Those From the Simha-somcynsmentioning

confidence: 99%

“…Shown are the data for hydrogen polymers (PIB , PS [Dlubek et al, 2004c], COP [Dlubek et al, 2007d], open symbols), PMPhS ( [Dlubek et al, 2007a], crosses), DGEBA (oligomer with six units [Dlubek et al, 2007b], stars), and fluoropolymers (PFE [Dlubek et al, 2004e], CYTOP [Dlubek et al, 2007c], amorphous Teflon AF1600 and AF2400 [Dlubek et al, 2008a;Rudel et al, 2008], all by filled symbols).…”

Section: Temperature Dependence Of the Free-volume Hole Sizementioning

confidence: 99%

“…Shown are the data for conventional polymers and fluoropolymers (VDF/HFP 22, a copolymer of vinylidene fluoride (78 mol%) and hexafluoropropylene (22 mol%) [Dlubek et al, 2004e], PFE, CYTOP, Teflon AF16000 and AF2400, crosses). As conventional polymers we consider here hydrogen polymers (aPP, an atactic polypropylene , PIB, PS, COP, open circles), siloxanes (PDMS, PMPhS, filled circles), poly(alkyl methacrylates) (PMMA, PEMA, PPMA, PBMA , filled up-triangles), monomeric and oligomeric DGEBA (filled stars), and further polymers (PC, polycarbonate [Dlubek et al, 2007d], SAN35, -a poly(styrene-co-acrylonitrile) with 35 mol% AN [Dlubek et al, 2004b], SMA50, a poly(styrene-co-maleic anhydride) with 50 mol% MA [Kilburn et al, 2005], PVC, poly(vinyl chloride) [Dlubek et al, 2003a], filled down-triangles) (abbreviations and references for other polymers as for Figure 11.5). The straight lines are linear fits to the data of conventional polymers constrained to intersect the origin.…”

Section: Temperature Dependence Of the Free-volume Hole Sizementioning

confidence: 99%

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Local Free‐Volume Distribution from PALS and Dynamics of Polymers

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Section: Comparison Of Pals Results With Those From the Simha-somcynsmentioning

confidence: 99%

Section: Comparison Of Pals Results With Those From the Simha-somcynsmentioning

confidence: 99%

Section: Comparison Of Pals Results With Those From the Simha-somcynsmentioning

confidence: 99%

Section: Temperature Dependence Of the Free-volume Hole Sizementioning

confidence: 99%

Section: Temperature Dependence Of the Free-volume Hole Sizementioning

confidence: 99%

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Local Free‐Volume Distribution from PALS and Dynamics of Polymers

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Positron Annihilation Spectroscopy

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FundamentalsThe positron is the antiparticle of the electron, ie, it has the opposite charge but otherwise the same properties. In matter, a positron may be created either by the β + decay of an unstable nucleus or from a high-energy γ-photon via e + -e − pair production. If the positron encounters an electron, both particles annihilate, ie, they are transformed into photons of an energy, which is given by the famous Einstein equation, E = 2mc 2 . Here, m is the mass of the electron, c the speed of light in vacuum, and for particles at rest E = 2 × 0.511 MeV. The selection rules for the γ-photon emission are derived from the conservation laws of energy and momentum and parity considerations. Free positrons annihilate mainly into two γ-photons of energy 0.511 MeV emitted in almost collinear directions, or with much less probability into three photons of an overall energy of 1.022 MeV (16,24,25).In nonconducting materials, such as polymers, positrons can exist as free particles (e + ) or as positronium (Ps, e + e − ), which is a positron-electron bound state. Ps was experimentally discovered by DeBenedetti and Richings in 1952 (26). The "chemical" symbol Ps for positronium appears to have been introduced by McGervey and DeBenedetti in 1959 (27). Its properties and interaction with matter were reviewed in several articles (25-30). Ps is a particle of the size of a hydrogen atom, r Ps = 0.53Å, but only the mass of two electrons, and a binding energy of 6.8 eV, that is half of the ionization energy of hydrogen. The lifetime of a Ps atom depends on the relative spin orientation of positron and electron. The para-Ps (p-Ps, singlet state, spins antiparallel) decays into two photons with a mean intrinsic lifetime (self-annihilation in a vacuum) of τ pPs 0 = 0.125 ns. The ortho-Ps (o-Ps, triplet state, spins parallel) can decay only into three photons, a much slower process than two-photon emission. Therefore, o-Ps has an intrinsic lifetime of τ oPs 0 = 142 ns. The formation probabilities of the p-Ps and o-Ps states are 0.25 and 0.75 of the total Ps yield (16,25).In condensed matter studies, 22 Na is usually used as the positron source. This isotope has a half-life of 2.6 years and emits positrons with an energy distribution that has its maximum at 0.20 MeV and ranges up to 0.54 MeV (10,16). The stopping profile of positrons is a decreasing exponential function. In materials with a density of 1 g/cm 3 50%, 90%, and 99% of positrons are stopped within a thickness of 0.170, 0.60, and 1.20 mm, respectively. The energetic positrons lose their energy rapidly via ionization and excitation of electrons and finally phonons. After a few picoseconds, the positrons are in thermal equilibrium with the ambient material. In defect-free molecular crystals, positrons migrate over a mean distance of typically 100 nm before annihilating. In defected crystals and in amorphous matter, positrons may annihilate from local free volumes. The mean positron lifetimes are typically τ e+ = 200-400 ps.

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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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The free volume in two untreated, pressure-densified, and CO2 gas exposed polymers from positron lifetime and pressure-volume-temperature experiments

Cited by 17 publications

References 0 publications

Local Free‐Volume Distribution from PALS and Dynamics of Polymers

Local Free‐Volume Distribution from PALS and Dynamics of Polymers

Positron Annihilation Spectroscopy

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

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