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Authors
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Dlubek, G. ; Supej, M. ; Bondarenko, V. ; Pionteck, J. ; Krause-Rehberg, R.
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Title
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Ortho-Positronium Lifetime Distribution Analyzed with MELT and LT and Free Volume in Poly(e-caprolactone during Glass Transition, Melting, and Crystallization
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Date
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31.12.2003
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Number
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10629
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Abstract
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Positron annihilation lifetime spectroscopy (PALS) was used to study the free volume behavior in the temperature range between 100 and 370 K in semicrystalline poly(<IMGSRC="/giflibrary/12/epsiv.gif"BORDER="0">-caprolactone) (PCL). For the analysis of the spectra we used the well-known routine MELT as well as the new program LT8.0, which allows both discrete and log-normal distributed annihilation rates. From experiments, confirmed by the analysis of simulated spectra, we found that MELT returns too large values for the <I>o</I>-Ps lifetime <IMGSRC="/giflibrary/12/tau.gif"BORDER="0"><SUB>3</SUB> associated with too small intensities <I>I</I><SUB>3</SUB>. This is due to the underestimation of the width of <I>o</I>-Ps lifetime distribution in MELT (the spectra analyzed contained 3 million counts). The same effects were observed in the parameters obtained from the discrete term analysis. LT, however, returns, when allowing the <I>o</I>-Ps lifetime to be distributed, rather accurate values for <IMGSRC="/giflibrary/12/tau.gif"BORDER="0"><SUB>3</SUB>, <I>I</I><SUB>3</SUB>, and th<br />e width (standard deviation <IMGSRC="/giflibrary/12/sigma.gif"BORDER="0"><SUB>3</SUB>) of the <I>o</I>-Ps lifetime distribution. The effect of the glass transition, melting, and crystallization on the annihilation parameters was observed. These results were compared with differential scanning calorimetry (DSC) and pressure-volume-temperature (PVT) experiments. From this comparison, the number density of holes and the fractional free (hole) volume have been estimated. At a <IMGSRC="/giflibrary/12/ldquo.gif"BORDER="0">knee<IMGSRC="/giflibrary/12/rdquo.gif"BORDER="0"> temperature <I>T</I><SUB><I>k</I></SUB> <IMGSRC="/giflibrary/12/ap.gif"BORDER="0"> 1.5 <I>T</I><SUB><I>g</I></SUB>, a leveling off of the <I>o</I>-Ps lifetime <IMGSRC="/giflibrary/12/tau.gif"BORDER="0"><SUB>3</SUB> and a distinct decrease in the width, <IMGSRC="/giflibrary/12/sigma.gif"BORDER="0"><SUB>3</SUB>, of its distribution was observed; the latter effect was detected for the first time. Fast motional processes and/or the disappearance of the dynamic heterogeneity of the glass and the transition to a homogeneous liquid are discussed as possible reasons for these effects. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3077-3088, 2003
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Publisher
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Journal of Polymer Science: Part B: Polymer Physics
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Wikidata
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Citation
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Journal of Polymer Science: Part B: Polymer Physics 41 (2003) 3077-3088
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DOI
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https://doi.org/10.1002/polb.10622
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