期刊
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
卷 12, 期 1, 页码 117-125出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.0c03211
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资金
- National Science Foundation, Division of Materials Research, Polymers Program [DMR-1905597]
- Chancellor's Fellowship, UTK
- German Research Foundation via the Transregional Center for Collaborative Research within the project, Polymers under multiple constraints: restricted and controlled molecular order and mobility [SFB TRR 102]
Experimental and simulation results demonstrate that molecular dynamics in ultrathin layers are influenced by interfacial regions with thicknesses very close to the glass transition temperature, which are relevant for applications of polymers in adhesion, coatings, and polymer nanocomposites.
Molecular dynamics in ultrathin layers is investigated using nanostructured electrodes to perform broadband dielectric spectroscopy measurements, and by atomistic molecular dynamics simulations. Using poly(vinyl acetate) as the model system and taking advantage of access to the distribution of relaxation times in an extended temperature range above the glass transition temperature, T-g, we demonstrate that while the mean rates of the segmental relaxation remain bulklike down to 12 nm film thickness, modified molecular mobilities arise in the interfacial zones. Combining results from simulations and experiments, we show unambiguously that both the slow relaxations arising from adsorbed polymer segments and the faster modes attributed to segments in the vicinity of the free interface have non-Arrhenius temperature activation. These interfacial regions span thicknesses of similar to 1.5 nm each just above the calorimetric T-g independent of molecular weight and film thickness. These deviations at interfaces are relevant for applications of polymers in adhesion, coatings, and polymer nanocomposites.
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