Irreversibly adsorbed polymer layers represent an intriguing class of novel nanomaterials with unexpected properties, strongly deviating from what observed in unbounded polymer melts. These extremely thin films are obtained via a small number of successive steps, easily reproducible: a polymer melt is placed in contact with an adsorbing substrate and nonadsorbed chains are washed away in a good solvent. Importantly, tuning the thickness of the adsorbed layer, an operational parameter equivalent to the number of chains adsorbed on a unit surface, allows modifying interfacial density and, hence, the performance of polymer coatings without affecting the interfacial chemistry.<br/>Here, we discuss on how broadband dielectric spectroscopy can be employed to investigate how adsorbed layers affect the dynamics of thin polymer melts. Due to the sensitivity of the technique to immobilization and orientational order, we study the impact of adsorption on the segmental mobility. We show that simple reasoning based on equilibrium approaches cannot explain the current experimental findings. In particular, the enhanced segmental motion commonly observed in spin cast thin polymer films is a nonequilibrium phenomenon. In the presence of nonrepulsive interfaces, prolonged annealing in the liquid state allows, in fact, recovering bulk segmental mobility. Our measurements prove that, while the fraction of unrelaxed chains increases upon nanoconfinement, the dynamics of equilibration is almost unaffected by the film thickness. We demonstrate that that the equilibration of the thin polymer melts is driven by the slow relaxation of interfacial chains upon irreversible adsorption on the confining walls.<br/>Our recent work verifies that the segmental relaxation of thin polymer coatings, adequately processed in nonequilibrium conditions, gets enhanced in proximity of rough substrates. This trend is in contrast to existing treatments of roughness which conclude it is a source of slower dynamics. Our experimental evidence indicates the faster interfacial dynamics originate from a reduction in interfacial density, due to the non-complete filling of substrate asperities. Importantly, our results agree with the same scaling that describes the density dependence of bulk materials, correlating segmental mobility to an exponential term of the specific volume.

Using dielectric spectroscopy to investigate the impact of irreversible adsorption on the dynamics of thin polymer melts

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

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