Papers by Author: Günter Dlubek

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Authors: Yang Yu, Günter Dlubek, Reinhard Krause-Rehberg, Mario Beiner, Elke Hempel
Abstract: Positron lifetime annihilation spectroscopy (PALS) was used to study the temperature- dependence of sub-nanometer size local free volumes in two atactic poly(n-octadecyl methacrylate)s (PODMA) with different molecular weight. These materials exhibit short range layered structure with a self-assembly and crystallization of side chains. From the ortho-positronium (o-Ps) lifetime the size of free volume holes and its distribution are calculated. At a temperature Tm=311 ± 5 K, the mean hole volume shows an abrupt and strong increase from 0.15 nm3 to 0.2 nm3, which comes from the melting of side-chains. The reverse effect, attributed to side chain crystallization, was observed during cooling the samples at slightly lower temperatures. The lifetime result of PODMA is compared with semifluorinated polyesters in which the side chain has an oxydecylperfluorodecyl structure (-O-(CH2)10-(CF2)9-CF3). Long chain polymers without side-chains such as polyethylene and short side-chain poly(n-alkyl methacrylate)s: poly(methyl methacrylate) (PMMA) and poly(n-hexyl methacrylate) (PHMA) are also compared with these polymers.
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Authors: Yang Yu, Günter Dlubek, Josef Bartoš, Helena Švajdlenková, Reinhard Krause-Rehberg
Abstract: In this work positron annihilation lifetime spectroscopy (PALS) is employed to study the ortho-Positronium lifetime parameters τ3>, σ3 and I3 in two structurally simple amorphous polymers 1,2-poly(butadiene) and cis-1,4-poly(isoprene). The ortho-Positronium mean lifetime parameter τ3> is compared with dynamics data from broadband dielectric spectroscopy (BDS) and electron spin resonance (ESR) experiments. Coincidences of characteristic temperatures from PALS with BDS and ESR experiments show close relationships between positron lifetime and dynamics of polymers.
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