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Chair of Physical Chemistry 1, Prof. Dr. Markus Retsch

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Direct measurement of the in-plane thermal diffusivity of semitransparent thin films by lock-in thermography: an extension of the slopes method

31. May 2019

Our work has been published in Analytical Chemistry. An extension of the well-known slopes method for characterization of the in-plane thermal diffusivity of semitransparent polymer films is presented. A theoretical model is introduced which considers heat losses due to convection and radiation mechanisms, as well as semitransparency of the material to the exciting laser heat source (visible range) and multiple reflections at the film surfaces. Most importantly, a potential semitransparency of the material in the IR detection range is also considered. It is proved by numerical simulations and by an asymptotic expansion of the surface temperature that the slopes method is also valid for any semitransparent film in the thermally thin regime. Measurements of the in-plane thermal diffusivity performed on semitransparent polymer films covering a wide range of absorption coefficients (to the exciting wavelength and in the IR detection range of our IR camera) validate our theoretical findings.

Full details can be found in DOI: https://doi.org/10.1021/acs.analchem.9b01583

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