Free-volume microstructure of amorphous polycarbonate at low temperatures determined by positron-annihilation-lifetime spectroscopy

Krištiak, J.; Bartoš, Josef; Krištiaková, K.; Šauša, O.; Bandžuch, P.

doi:10.1103/physrevb.49.6601

Cited by 68 publications

(49 citation statements)

References 24 publications

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“…Higuchi and Simha [1996] have tested Eq. (12.14) at low temperatures (50 K < T < 350 K) in the glassy state of polycarbonate, using I 3 and v h data of Kristiak et al [1994] and V-T data of Roe et al Roe, 1973;Roe and Simha, 1974]. Excellent agreement between the two quantities was found at temperatures down to 130 K, with a value V occ , which is numerically in excellent agreement with the S-S value calculated via Eq.…”

Section: The Simha-somcynsky Equation-of-state Theorysupporting

confidence: 74%

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: The Simha-somcynsky Equation-of-state Theorysupporting

confidence: 74%

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

2010

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“…[45,47,61 -65] Since a occ is usually not known, several authors use the approximation a occ ¼ a g . [47,[61][62][63][64][65] Other groups have assumed a occ ¼ 0. [45] As our results from Figure 2.…”

Section: Hole Density From the Comparison Of Pals And Pvt Resultsmentioning

confidence: 99%

The Structure of the Free Volume in Poly(styrene‐co‐acrylonitrile) from Positron Lifetime and Pressure Volume Temperature (PVT) Experiments

Dlubek

Бондаренко

Al-Qaradawi

et al. 2004

Macro Chemistry & Physics

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Summary: The structure of the free volume and its temperature dependence between 25 and 190 °C of copolymers of styrene with acrylonitrile, SAN (0 to 50 mol‐% AN), is studied by pressure volume temperature (PVT) experiments and positron annihilation lifetime spectroscopy (PALS). In this second part of the work, PALS data are reported from which the temperature dependence of the mean size and size distribution of local free volumes (subnanometer size holes) is analysed. The mean hole volume, vh, varies in PS between 105 Å3 (27 °C) and 220 Å3 (190 °C), and shows a systematic decrease with increasing AN content, at Tg from 121 Å3 for PS to 102 (±2) Å3 for SAN50. The specific number of holes, $N_{\rm h} '$, estimated from a comparison of PVT and PALS results, is independent on the temperature and the composition of SAN, $N_{\rm h} '$ = (0.56 ± 0.02) × 1021 g−1 which corresponds to Nh(Tg) = $N_{\rm h} '$/V(Tg) = 0.59 nm−3 and 1/Nh(Tg) = 1.7 nm3 for the volume which contains one hole. The analysed size distributions of the holes above Tg follow the compressibility of the free volume as it is predicted by the theory of thermal volume fluctuation. Moreover, we showed that the bulk elasticity modulus follows mastercurves as a function of vh above and below Tg.Free volume hole radius distribution n(rh) in PS for three different temperatures.magnified imageFree volume hole radius distribution n(rh) in PS for three different temperatures.

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“…Measurements at higher temperatures above room temperature up to 350 K were performed in a chamber without vacuum. The stability of the temperature was about 1 K. 49 The positron lifetime spectra were analyzed using the well-known PATFIT-88 software package 50 in terms of a short-term component from the annihilation of parapositronium p-Ps, τ 1 , an intermediate one attributed to "free" positron annihilation, τ 2 , and a long-term one related to free volume due to the pick-of annihilation of orthopositronium o-Ps, τ 3 . The acquisition time was at least 2 h for each temperature.…”

Section: B Pals Methodsmentioning

confidence: 99%

Positron annihilation and relaxation dynamics from dielectric spectroscopy and nuclear magnetic resonance: Cis–trans-1,4-poly(butadiene)

Bartoš

Šauša²,

Schwartz

et al. 2011

The Journal of Chemical Physics

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The electronic spectrum of SiH4: Jahn-Teller Rydberg series J. Chem. Phys. 135, 214304 (2011) Electronic states of tetrahydrofuran molecules studied by electron collisions J. Chem. Phys. 135, 134317 (2011) Dyson orbitals of N2O: Electron momentum spectroscopy and symmetry adapted cluster-configuration interaction calculations J. Chem. Phys. 134, 204304 (2011) Electronic excitations of potassium intercalated manganese phthalocyanine investigated by electron energy-loss spectroscopy J. Chem. Phys. 134, 194504 (2011) Experimental and theoretical study on generalized oscillator strengths of the valence-shell electronic excitations in CF4 J. Chem. Phys. 134, 064307 (2011) Additional information on J. Chem. Phys. We report a joint analysis of positron annihilation lifetime spectroscopy (PALS), dielectric spectroscopy (BDS), and nuclear magnetic resonance (NMR) on cis-trans-1,4-poly(butadiene) (c-t-1, 4-PBD). Phenomenological analysis of the orthopositronium lifetime τ 3 − T dependence by linear fitting reveals four characteristic PALS temperatures:. Slight bend effects in the glassy and supercooled liquid states are related to the fast or slow secondary β process, from neutron scattering, respectively, the latter being connected with the trans-isomers. In addition, the first bend effect in the supercooled liquid coincides with a deviation of the slow effective secondary β eff relaxation related to the cis-isomers from low-T Arrhenius behavior to non-Arrhenius one and correlates with the onset of the primary α process from BDS. The second plateau effect in the liquid state occurs when τ 3 becomes commensurable with the structural relaxation time τ α (T b2 ). It is also approximately related to its crossover from non-Arrhenius to Arrhenius regime in the combined BDS and NMR data. Finally, the combined BDS and NMR structural relaxation data, when analyzed in terms of the two-order parameter (TOP) model, suggest the influence of solidlike domains on both the annihilation behavior and the local and segmental chain mobility in the supercooled liquid. All these findings indicate the influence of the dynamic heterogeneity in both the primary and secondary relaxations due to the cis-trans isomerism in c-t-1,4-PBD and their impact into the PALS response.

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Free-volume microstructure of amorphous polycarbonate at low temperatures determined by positron-annihilation-lifetime spectroscopy

Cited by 68 publications

References 24 publications

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

The Structure of the Free Volume in Poly(styrene‐co‐acrylonitrile) from Positron Lifetime and Pressure Volume Temperature (PVT) Experiments

Positron annihilation and relaxation dynamics from dielectric spectroscopy and nuclear magnetic resonance: Cis–trans-1,4-poly(butadiene)

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