Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 14: Poster: Glasses I (jointly with DY)

CPP 14.2: Poster

Tuesday, March 27, 2012, 18:15–20:15, Poster A

Segmental and chain dynamics of polyisoprene confined in thin layers — •Emmanuel Urandu Mapesa, Martin Tress, and Friedrich Kremer — Institute for Experimental Physics I, University of Leipzig, 04103 Leipzig, Germany

Broadband Dielectric Spectroscopy (BDS) - in combination with a nanostructured electrode arrangement - is used to study thin layers of cis-1,4-polyisoprene (cis-PI). cis-PI belongs to a special type of polymers because a part of its molecular dipole moment attached to each monomer unit is aligned along the main chain. This fraction adds up to one dipole moment of the whole polymer chain corresponding to the end-to-end vector of the molecule. Consequently, the investigation of two distinct relaxation modes taking place at two different length scales is possible: the segmental motion which involves structures of about one nanometer in size, and the normal mode which represents the dynamics of the whole macromolecule. In the current study, where highly insulating silica nanostructures are used as spacers, the need to evaporate a counter-electrode is circumvented. The spin-cast samples are checked before and after dielectric measurement so as to exclude the possibility of dewetting affecting the measured dynamics. Down to 7 nm, for three molecular weights (44.5, 53 and 75 kg/mol), it is observed that: (i) the segmental mode (and hence the dynamic glass transition) is unaffected by 1-D confinement, and (ii) the normal mode becomes faster with decreasing layer thickness in dependence on molecular weight.