Confinement and localization effects revealed for thin films of the miscible blend poly(vinyl methyl ether)/polystyrene with a composition of 25/75 wt%⋆
Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205, Berlin, Germany
* e-mail: Andreas.Schoenhals@bam.de
Accepted: 16 July 2019
Published online: 12 August 2019
Thin films (200-7nm) of the asymmetric polymer blend poly(vinyl methyl ether) (PVME)/polystyrene (PS) (25/75wt%) were investigated by broadband dielectric spectroscopy (BDS). Thicker samples (37 nm) were measured by crossed electrode capacitors (CEC), where the film is capped between Al-electrodes. For thinner films (37 nm) nanostructured capacitors (NSC) were employed, allowing one free surface in the film. The dielectric spectra of the thick films showed three relaxation processes ( -, - and -relaxation), like the bulk, related to PVME fluctuations in local spatial regions with different PS concentrations. The thickness dependence of the -process for films measured by CECs proved a spatially heterogeneous structure across the film with a PS-adsorption at the Al-electrodes. On the contrary, for the films measured by NSCs a PVME segregation at the free surface was found, resulting in faster dynamics, compared to the CECs. Moreover, for the thinnest films (26 nm) an additional relaxation process was detected. It was assigned to restricted fluctuations of PVME segments within the loosely bounded part of the adsorbed layer, proving that for NSCs a PVME enrichment takes place also at the polymer/substrate interface.
Key words: Topical issue: Dielectric Spectroscopy Applied to Soft Matter
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature, 2019