Calorimetric evidence for a mobile surface layer in ultrathin polymeric films: poly(2-vinyl pyridine)

Specific heat spectroscopy was used to study the dynamic glass transition of ultrathin poly(2-vinyl pyridine) films (thicknesses: 405-10 nm). The amplitude and the phase angle of the differential voltage were obtained as a measure of the complex heat capacity. In a traditional data analysis, the dyn...

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Bibliographic Details
Published in:Soft matter 2015-01, Vol.11 (4), p.7942-7952
Main Authors: Madkour, Sherif, Yin, Huajie, Füllbrandt, Marieke, Schönhals, Andreas
Format: Article
Language:English
Subjects:
Calorimetry
Dynamic tests
Dynamics
Film thickness
Heat capacity
Pyridines
Specific heat
Surface layer
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Summary:Specific heat spectroscopy was used to study the dynamic glass transition of ultrathin poly(2-vinyl pyridine) films (thicknesses: 405-10 nm). The amplitude and the phase angle of the differential voltage were obtained as a measure of the complex heat capacity. In a traditional data analysis, the dynamic glass transition temperature T g is estimated from the phase angle. These data showed no thickness dependency on T g down to 22 nm (error of the measurement of ±3 K). A derivative-based method was established, evidencing a decrease in T g with decreasing thickness up to 7 K, which can be explained by a surface layer. For ultrathin films, data showed broadening at the lower temperature side of the spectra, supporting the existence of a surface layer. Finally, temperature dependence of the heat capacity in the glassy and liquid states changes with film thickness, which can be considered as a confinement effect. Specific heat spectroscopy was used to study the dynamic glass transition of ultrathin poly(2-vinyl pyridine) films (thicknesses: 405-10 nm).
ISSN:1744-683X
1744-6848
DOI:10.1039/c5sm01558h