Dresden 2003 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 13: Dünne Polymerfilme

CPP 13.3: Talk

Thursday, March 27, 2003, 10:45–11:00, ZEU/118

A novel confinement-induced relaxation process in thin films of cis-polyisoprene — •Anatoli Serghei and Friedrich Kremer — Institute for Experimental Physics I, Linnestrasse 5, 04103 Leipzig

Broadband Dielectric Spectroscopy is employed to investigate the molecular dynamics of thin layers of cis-1,4-polyisoprene (PI) down to film thicknesses smaller than the end-to-end distance of the PI chains. Two relaxation processes are observed in the bulk, which take place on two different length scales: the segmental mode (corresponding to the dynamic glass transition) and the normal mode, which originates from the relaxation of the end-to-end vector of the chain. With decreasing film thickness a novel confinement-induced mode is observed between the segmental and the normal relaxation process. It becomes faster with increasing confinement and does not show a molecular weight dependence. It is assigned to fluctuations of terminal subchains which are formed due to the immobilization of chain segments at an interface. In contrast, the segmental and the normal mode are not affected in their relaxation rate down to thicknesses of 2 Ree, but the dielectric strength of the normal mode shows a steep decline with decreasing thickness. Simulations of the chains as ideal random walkers reveal the existence of a confinement-induced and thickness dependent distribution for the terminal subchains, which arises from chains immobilized at one interface and reflected at the other one. It is shifted to shorter values with increasing confinement and does not show a molecular weight dependence, in full agreement with the experiment.