Unveiling the Dynamics of Self-Assembled Layers of Thin Films of Poly(vinyl methyl ether) (PVME) by Nanosized Relaxation Spectroscopy.
A combination of nanosized dielectric relaxation (BDS) and thermal spectroscopy (SHS) was utilized to characterize the dynamics of thin films of poly(vinyl methyl ether) (PVME) (thicknesses: 7-160 nm). For the BDS measurements, a recently designed nanostructured electrode system is employed. A thin film is spin-coated on an ultraflat highly conductive silicon wafer serving as the bottom electrode. As top electrode, a highly conductive wafer with nonconducting nanostructured SiO2nanospacers with heights of 35 or 70 nm is assembled on the bottom electrode. This procedure results in thin supported films with a free polymer/air interface. The BDS measurements show two relaxation processes, which are analyzed unambiguously for thicknesses smaller than 50 nm. The relaxation rates of both processes have different temperature dependencies. One process coincides in its position and temperature dependence with the glassy dynamics of bulk PVME and is ascribed to the dynamic glass transition of a bulk-like layer in the middle of the film. The relaxation rates were found to be thickness independent as confirmed by SHS. Unexpectedly, the relaxation rates of the second process obey an Arrhenius-like temperature dependence. This process was not observed by SHS and was related to the constrained fluctuations in a layer, which is irreversibly adsorbed at the substrate with a heterogeneous structure. Its molecular fluctuations undergo a confinement effect resulting in the localization of the segmental dynamics. To our knowledge, this is the first report on the molecular dynamics of an adsorbed layer in thin films.
Bundesanstalt für Materialforschung und Prüfung (BAM) , Unter den Eichen 87, 12205 Berlin, Germany.
Sherif
S
Madkour
Bundesanstalt für Materialforschung und Prüfung (BAM) , Unter den Eichen 87, 12205 Berlin, Germany.
Paulina
P
Szymoniak
Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin , Straße des 17, Juni 124, 10623 Berlin, Germany.
Mojdeh
M
Heidari
Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin , Straße des 17, Juni 124, 10623 Berlin, Germany.
Regine
R
von Klitzing
Bundesanstalt für Materialforschung und Prüfung (BAM) , Unter den Eichen 87, 12205 Berlin, Germany.
Andreas
http://orcid.org/0000-0003-4330-9107
A
Schönhals
AC-nanochip calorimetry; adsorbed layer dynamics; broadband dielectric spectroscopy; dynamic glass transition; nanostructured capacitors; poly(vinyl methyl ether); thin films