Broadband dielectric spectroscopy on miscible polymer blends in the bulk and in nanometer thick films - Comparison of the different confinement situations*

Broadband dielectric spectroscopy in the frequency range from 10^-1 to 10⁹ Hz is employed to revisit the segmental dynamics of the miscible blend system of poly(vinyl methyl ether)/polystyrene (PVME/PS) in dependence on the composition first in the bulk state. Here, the case of high polystyrene concentrations is considered especially. It is important to note that the dipole moment of polystyrene is negligible, thus only the molecular dynamics of PVME segments, as affected by PS, is observed. Three relaxation processes are found, which are due to fluctuations of differently constrained or confined PVME segments. The degree of the confinement of PVME segments due to PS is discussed in dependence on the composition.
Secondly, a spatial confinement is considered by investigating thin films of the PVME/PS blend, where the film thickness varies from 100 nm down to 5 nm. Two concentrations of PVME/PS (50/50 wt% and 25/75 wt%) are investigated. To measure nanometer thick films a novel electrode system based on nanostructured electrodes was employed. Nanostructured electrodes can be considered as a cut-edge technology in dielectric spectroscopy. The relaxation spectra of the films showed multiple processes, which are discussed in dependence on the film thickness.