Threshold temperature sensors with tunable properties

Thermochromic polymer/dye blends based on small amounts (0.6-2.3 wt.-%) of chromogenic sensor dyes and glassy amorphous polymers were prepared. Subjecting melt-processed, quenched blends to temperatures above T-g leads to permanent and pronounced changes of their absorption and fluorescence spectra as a result of phase separation and assembly of dye aggregates. The influence of dye structure and polymer Tg on the aggregation kinetics of these blends was investigated. It is shown that increasing the length of the dye's rigid core leads to slower aggregation rates due to limited mobility in the polymer. The threshold of the color change can be tailored by adjusting the polymer Tg, as was shown by the systematic investigation of blends based on poly(alkyl methacrylate) copolymers of varying composition.