Thermochromie und die Funktionsweise von Thermopapier: Das Experiment.

Summary Facsimile paper, so‐called thermal paper, is an example for thermographic recording material which is utilised for fast printing of receipts and tickets. These papers consist of a thermochromic three‐component mixture of a colourless leuco dye and a weak acidic developer mixed with a high melting long‐chain alcohol solvent. The developer is encapsulated in the solvent and therefore not able to protonate the pH‐sensitive leuco dye molecules to build the coloured state of the mixture. A striking colour change occurs upon heating the composition and melting the solvent whereby the developer is free to react with the leuco dye. Thermochromic composites formulated from the colour former Crystal Violet lactone (CVL), an alkyl gallate as developer and 1‐tetradecanol as solvent are presented in this article. The simple contact with hot water leads to colour reaction on thermal paper, whereas no colour change occurs after contact with hot oil. Based on these phenomena on thermal paper, we have found an interesting concept to demonstrate thermochromic behaviour for science education in school. [ABSTRACT FROM AUTHOR]