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Authors
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Kilburn, D. ; Dlubek, G. ; Pionteck, J. ; Häßler, R. ; Alam, M. A.
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Title
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Temperature and Pressure Dependence of the Free Volume in Polyisobutylene from Positron Lifetime and Pressure-Volume-Temperature Experiments
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Date
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08.05.2006
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Number
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13604
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Abstract
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<B>Summary:</B> The microstructure of the free volume and its temperature and pressure dependence in PIB were studied by PVT experiments and PALS. Employing the Simha-Somcynsky equation of state, the hole-free volume fraction <I>h</I> and the specific free and occupied volumes, <I>V</I><SUB>f</SUB> = <I>hV</I> and <I>V</I><SUB>occ</SUB> = (1 - <I>h</I>)<I>V</I>, respectively, and their expansivity and compressibility were calculated. From the PALS spectra analyzed using the LT9.0 software, the hole size distribution, the mean hole size <IMGSRC="/giflibrary/12/lang.gif"BORDER="0"><I>v</I><SUB>h</SUB><IMGSRC="/giflibrary/12/rang.gif"BORDER="0"> and mean dispersion <I><IMGSRC="/giflibrary/12/sigma.gif"BORDER="0"></I><SUB>h</SUB> were calculated. From a comparison of <IMGSRC="/giflibrary/12/lang.gif"BORDER="0"><I>v</I><SUB>h</SUB><IMGSRC="/giflibrary/12/rang.gif"BORDER="0"> with <I>V</I><SUB>f</SUB>, the hole density <IMGBORDER="0"ALIGN="ABSMIDDLE"SRC="http://www3.interscience.wiley.com/cgi-bin/TeX2gif.pl?%24N'_%7B%5Crm%20h%7D%24"> was obtained. It was found that PIB shows an unusual thermal expansion with glass-like transitions at 210 K and 290 K (at 0 MPa). A similar behavior is observed for tan <I><IMGSRC="/giflibrary/12/delta.gif"BORDER="0<br />"></I>. It was found that at 296 K, <IMGSRC="/giflibrary/12/lang.gif"BORDER="0"><I>v</I><SUB>h</SUB><IMGSRC="/giflibrary/12/rang.gif"BORDER="0"> decreases exponentially from 80 Å<SUP>3</SUP> at 0.1 MPa to the extremely low value of 10 Å<SUP>3</SUP> at 1 300 MPa. Starting from a fluctuation approach, the free-volume fluctuations and the characteristic length scale (<I><IMGSRC="/giflibrary/12/xi.gif"BORDER="0"></I>) of dynamic heterogeneity of structural relaxation were estimated from <I><IMGSRC="/giflibrary/12/sigma.gif"BORDER="0"></I><SUB>h</SUB>. It was found that <I><IMGSRC="/giflibrary/12/xi.gif"BORDER="0"></I> increases from <IMGSRC="/giflibrary/12/ap.gif"BORDER="0">1.5 nm to <IMGSRC="/giflibrary/12/ap.gif"BORDER="0">1.9 nm when the temperature decreases from 293 K to the glass transition temperature <I>T</I><SUB>g</SUB> = 207 K (at 0 MPa) or the pressure increases from 0.1 MPa to 200 MPa (at 296 K).
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Publisher
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Macromolecular Chemistry and Physics
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Wikidata
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Citation
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Macromolecular Chemistry and Physics 207 (2006) 721-734
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DOI
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https://doi.org/10.1002/macp.200600013
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Tags
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