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A Simplified Method for the Estimation of Hole Free Volume Fraction from the Specific Volume

100%
Dlubek G., Pionteck J.
|
EN
A brief introduction in the equation of state of the Simha-Somcynsky hole theory is presented. This theory allows to calculate the volume fraction h of free volume holes from pressure-volume-temperature experiments. These holes are detected by ortho-positronium and from the value of h and the mean ortho-positronium hole size the hole density may be calculated. We discuss a simplified method to estimate h which makes use of the relation V* = 1.52V_W between the scaling volume V* of the Simha-Somcynsky hole theory equation of state and the van der Waals volume V_W. Moreover, we present a new simplified method for the estimation of h which starts with the Schottky (Arrhenius) equation for the concentration of thermal vacancies and makes use of a linear relation between the scaling temperature T* and the hole formation enthalpy H_h, H_h(kJ/mol)=6.54×10^{-4}T*(K).
2
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Gas Pressure Induced Porosity of CYTOP Polymer. A~Positron Study

71%
Zgardzińska B., Goworek T., Śniegocka M., Zaleski R., Dlubek G.
Acta Physica Polonica A
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2014
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vol. 125
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issue 3
782-784
EN
The pore formation in CYTOP polymer under high pressure of argon or nitrogen gases was investigated by positron annihilation spectroscopy. In the range 0-70 MPa, formation of large open pores was observed. After reduction of pressure to normal one, the free volumes inside the polymer structure remained enlarged. The structure of CYTOP can be restored by applying the temperature over 470 K at normal pressure.
3
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Relations Between Hole Volume and Macroscopic Volume in Various Polymers

71%
Dlubek G., Alam M., Saarinen K., Stejny J., Fretwell H.
Acta Physica Polonica A
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1999
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vol. 95
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issue 4
521-526
EN
Different definitions of the free volumes are discussed and related to the total specific volume and to the local free (hole) volume. Positron lifetime measurements are reported for polyethylene, polytetrafluoroethylene, and CR39-copolymers. Two long-lived components appear in polyethylene and polytetrafluoroethylene, which were attributed to o-Ps annihilations in crystalline regions and in holes of the amorphous phase. From a relation between the coefficients of the thermal expansion of macroscopic and hole volume, the fractional hole volume h and from this the number of holes, N, is estimated. Values of T_{g}=195 K, h_{g}=4.5% (polyethylene) and 5.7% (polytetrafluoroethylene) and N_{g}=0.73 nm^{-3} (polyethylene) and 0.36 nm^{-3} (polytetrafluoroethylene) were obtained. In semicrystalline polymers these values agree with estimates obtained from the densities of the crystalline and amorphous phases. The effect of cross-linking on the free-volume properties of CR39-copolymer networks was studied. The comparison of the hole volume with the specific volume allowed us to estimate the number density of holes to ≈1 nm^{-3}.
4
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The Temperature and Pressure Dependence of the Free Volume in Fluoroelastomers from PALS and PVT Experiments

52%
Dlubek G., Sen Gupta A., Wawryszczuk J., Kilburn D., Pionteck J., Krause-Rehberg R., Goworek T., Alam M., Kaspar H., Lochhaas K.
Acta Physica Polonica A
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2005
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vol. 107
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issue 4
685-689
EN
Positron lifetime and pressure-volume-temperature experiments were performed as function of T (100-485 K) and P (10^{-5} Pa-500 MPa) on a fluoroelastomer. From positron annihilation lifetime spectroscopy, analyzed with LT9.0 assuming a dispersion in the e^+ (τ_2) and o-Ps (τ_3) lifetime, the mean, 〈v_h〉, and the width (standard deviation), σ_h, of the hole size distribution were calculated. The pressure-volume-temperature data were analyzed using the Simha-Somcynsky hole-lattice theory to estimate the specific hole free volume V_f. From a comparison of V_f with 〈v_h〉 the specific hole number, N'_h, is estimated. The data from thermal expansion and pressure experiments show complete agreement when taking into account the compressibility of the occupied volume.
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