Due to its extraordinary wide dynamic range, covering more 15 decades in time or frequency, broadband dielectric spectroscopy (BDS) has been widely used to characterize the molecular dynamics in polymers, organic liquids and solids. Since dielectric relaxation processes sense fluctuations of molecular dipoles driven by molecular motions on various length scales, BDS can provide deep insights in molecular dynamic processes involving simple bond rotations, segmental dynamics (the dynamic glass transition) or even whole molecule reorientations. A prerequisite for the application of BDS is the presence of dipoles, which provides the link between molecular motions and the interactions with an external electrical field. Though most of the polymer systems contain at least weakly polar groups in either the main or the side chains, a substantial class of nonpolar polymers, for example polyolefins, do not. A successful strategy to make molecular relaxation “visible” to BDS is the addition of rigid molecules acting as “dielectric probes” in analogy to the well-established fluorescent probe techniques. Our approach, developed and refined in the past 15 years, relies on the fact that the strength of a dielectric relaxation Δε scales according to Δε∝μ2 , i.e. depends on the concentration n and the square of the molecular dipole moment μ2. Because of this scaling, a substantial enhancement of the dielectric α-relaxation already at “doping” levels less than 1wt% using the highly polar probe molecule E-4,4’-N,N-dibutylamino-nitro-stilbene (DBANS) could be achieved as demonstrated for isotactic polypropylene (iPP), polyethylene (LDPE) and polystyrene (PS). This presentation will give an introduction into probe-enhanced BDS and will then focus on various specific applications of dielectric probes: - Study of glass transition dynamics in nonpolar systems, - Probe response in relation to dynamic heterogeneities, - Spatially resolved dynamic information in ultrathin polymer films, and - Tracer diffusion studied by dielectric probes in multi-layer systems.

Dielectric probes: Versatile tool for the study of molecular dynamics in polymers

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.