Visual detection of the topology freezing transition temperature of vitrimers based on fluorescein-soaked coatings from photonic crystals and vitrimers

Abstract

The topology freezing transition temperature (T_v) of vitrimers is a key parameter for their application. Common methods for detection of T_v include the use of rheology and dynamic mechanical analysis under external force, but external force may affect T_v. Herein, a visual detection method for T_v is proposed based on fluorescein-soaked photonic coatings from lower photonic crystals (PCs) and upper vitrimers. Because PCs have photonic band gaps (or structural colors), by combining different structural colors of PCs and the fluorescence of vitrimers soaked with fluorescein, when the heating temperature is higher than T_v of the vitrimer, the ester (or carboxyl) group of fluorescein undergoes ester exchange with the ester group in vitrimers, and the color and fluorescence intensity of photonic coatings show great changes. T_v of vitrimers is easily obtained according to these obvious changes and it is unaffected by the use of a different fluorescein. Accurate fluorescence spectra can be measured to further identify the T_v of vitrimers. The lower PCs enhance the sensitivity of T_v detection for vitrimers. The visual detection method is simple, non-damaging, and accurate, has good reliability and universality, and does not require expensive equipment.