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Printable Optical Sensors Based on H-Bonded Supramolecular Cholesteric Liquid Crystal Networks

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journal contribution
posted on 09.05.2012, 00:00 by Nicole Herzer, Hilal Guneysu, Dylan J. D. Davies, Derya Yildirim, Antonio R. Vaccaro, Dirk J. Broer, Cees W. M. Bastiaansen, Albertus P. H. J. Schenning
A printable H-bonded cholesteric liquid crystal (CLC) polymer film has been fabricated that, after conversion to a hygroscopic polymer salt film, responds to temperature and humidity by changing its reflection color. Fast-responding humidity sensors have been made in which the reflection color changes between green and yellow depending on the relative humidity. The change in reflection band is a result of a change in helix pitch in the film due to absorption and desorption of water, resulting in swelling/deswelling of the film material. When the polymer salt was saturated with water, a red-reflecting film was obtained that can potentially act as a time/temperature integrator. Finally, the films were printed on a foil, showing the potential application of supramolecular CLC materials as low-cost, printable, battery-free optical sensors.