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PO: Polymerphysik
PO 10: Poster: Mechanische Eigenschaften und Bruchverhalten
PO 10.7: Poster
Montag, 17. März 1997, 15:30–17:30, Gg
A high-pressure ramanspektroscopic study of the phase behavior of alkanes, cycloalkanes and semifluorinated alkanes with respect to the phase behavior of PE and PTFE — •J. M"uller, K. Weishaupt, and M. Pietralla — Universit"at Ulm, Abt. Experimentelle Physik
Raman spectra were obtained under hydrostatic pressure up to 15 kbar and from room temperature up to the melt. In these studies a sapphire pressure cell similar to a diamond anvil cell was used. It is well known, that the solid- solid phase transitions of the cycloalkanes C22H44 and C24H48 which are appearing at normal presssure a few degrees below melting, is a phase transition to the conformational disordered (Condis) phase. It is shown in this work, that the temperature range where the condis phase existes, increases with pressure. For longer cycloalkanes we have been able to show, that a Condis phase exists at elevated pressure. The phase diagram lookes similar to that of PE. From previos ramanspectroscopic studies it is know, that the solid- solid phase transition of the semifluorinated alkanes CF3(CF2)11(CH2)nCH3 with 4<n<14 at normal pressure is a transition to liquid cristall (smectic A), where the hydrogenated part of the molecule is conformational disordered. It was possible to show, that for the molecules with longer hydrogenated parts, the melting process splits in to transitions under elevated pressure. We also made raman measurements at high-pressure from the normal alkanes C10H22 to C14H30 with respect to their phase behavior.