Glass transition of nanometric polymer films probed by picosecond ultrasonics

D Brick; M Hofstetter; P Stritt; J Rinder; V Gusev; T Dekorsy; M Hettich

doi:10.1016/j.ultras.2021.106630

Glass transition of nanometric polymer films probed by picosecond ultrasonics

Ultrasonics. 2022 Feb:119:106630. doi: 10.1016/j.ultras.2021.106630. Epub 2021 Oct 21.

Authors

D Brick¹, M Hofstetter¹, P Stritt¹, J Rinder¹, V Gusev², T Dekorsy³, M Hettich⁴

Affiliations

¹ Department of Physics, University of Konstanz, 78464 Konstanz, Germany.
² Laboratoire d'Acoustique de l'Université du Mans (LAUM), UMR 6613, Institut d'Acoustique - Graduate School (IA-GS), CNRS, Le Mans Université, Av. O. Messiaen, 72085 Le Mans, France.
³ Department of Physics, University of Konstanz, 78464 Konstanz, Germany; Institute of Technical Physics, German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany.
⁴ Department of Physics, University of Konstanz, 78464 Konstanz, Germany; Research Center for Non-Destructive Testing GmbH, Altenbergerstr. 96, 4040 Linz, Austria.. Electronic address: mike.hettich@recendt.at.

PMID: 34735929
DOI: 10.1016/j.ultras.2021.106630

Abstract

The possibility to measure the glass transition temperature in poly(methyl methacrylate) (PMMA) films by picosecond ultrasonics with thicknesses ranging from 458 nm to 32 nm is demonstrated. A shift of the longitudinal acoustic eigenmodes towards lower frequencies with temperature is observed accompanied by a change in the temperature-frequency slopes at the glass transition temperature. The contributions to the frequency shift from changes in film thickness and sound velocity are discussed and the latter is extracted below the glass transition temperature. Finally, the advantages and disadvantages of the current approach in a comparison to other methods based on acoustic measurements in the GHz regime are reviewed.

Keywords: ASOPS; Glass transition; Picosecond ultrasonics; Polymer; Thin films.