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The last decades have seen a large development of functional coatings, which often leads to high-tech assemblies. In order to ensure the durability and functionality of such systems, there is a specific need for characterisation at a low scale since the properties of thin materials may differ from those of bulk ones. The nature of coatings also often asks for caution when used in different operating conditions. This work deals with the adaptation of a classical interferometry technique to the expansion characterisation in a specific material configuration: thin films made of potential conditionssensitive materials. Despite being known for ages, the Michelson interferometer has scarcely been used for characterisation of properties in materials science1. Following a variation of a multi-reflection interferometer proposed back in 19822, we propose an adaptation of the Michelson interferometer that allows quantifying the coefficients of expansion of thin polymeric materials, inducing some technical challenges which needed to be coped. After we tackle the experimental issues inherent to those innovative improvements, the validation of the technique is performed by measuring accurately the expansions under several experimental conditions of various specimens made of five different well-known thermoplastics and a polysaccharide used extensively in food packaging. The accuracy of the measurements is estimated. The reliability of the device developed in the laboratory applied to the characterisation of the thin films is discussed as well as the advantages and limitations of the technique. Through the material examples used, we point out the benefits of this technique in materials science characterisation, notably by reporting interesting behaviours of specimens barely explored in the literature so far.
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