Time–Temperature Integrating Optical Sensors Based on Gradient Colloidal Crystals

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Schöttle, Marius ; Tran, Thomas ; Feller, Tanja ; Retsch, Markus:
Time–Temperature Integrating Optical Sensors Based on Gradient Colloidal Crystals.
In: Advanced Materials. Bd. 33 (2021) Heft 40 . - 2101948.
ISSN 1521-4095
DOI: https://doi.org/10.1002/adma.202101948

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Abstract

Manipulation-free and autonomous recording of temperature states for extended periods of time is of increasing importance for food spoilage and battery safety assessment. An optical readout is preferred for low-tech visual inspection. Here, a concept for time–temperature integrators based on colloidal crystals is introduced. Two unique features in this class of advanced materials are combined: 1) the film-formation kinetics can be controlled by orders of magnitude based on mixtures of particles with distinct glass transition temperatures. 2) A gradual variation of the particle mixture along a linear gradient of the colloidal crystal enables local readout. Tailor-made latex particles of identical size but different glass transition temperatures provide a homogenous photonic stopband. The disappearance of this opalescence is directly related to the local particle ratio and the exposure to a time and temperature combination. This sensing material can be adjusted to report extended intermediate and short excessive temperature events, which makes it specifically suitable for long-term tracing and threshold applications.