Colorimetric concentration detection based on photonic crystals has attracted considerable attention owing to the substantial color changes in response to external stimuli. In general, photonic crystals for colorimetric detection are carefully designed by introducing tailored recognition sites into an ordered structure. These materials are widely used in the detection of trace substances. However, the traditional photonic crystal assembled by colloid particles was rarely applied in concentration detection since the solute tends to occupy the interparticle voids, causing reduced refractive index contrasts and closed bandgaps at higher concentrations. Consequently, the development of a more convenient and universal concentration detection material is an urgent requirement. Herein, photonic crystals assembled by mesoporous SiO2 particles (m-SiO2–PC) were prepared and used as a colorimetric indicator of solution concentration for nonvolatilized substances. The solute preferentially occupied the mesopores of m-SiO2 particles, yielding an increase in reflection index, a shift in reflection peak, and considerable color contrasts on the m-SiO2–PC film after the evaporation of solvent. The relation between wavelength shifts and solution concentrations could be used for quantitative concentration detection. A colorimetric concentration indicator based on m-SiO2–PC film provides a more efficient and universal method that is applicable for a variety of solutions.
Topology freezing transition temperature (Tv) of vitrimers is an important indicator for their applications. Tvof vitrimers could be changed by using chemical methods. Herein, a physical method is proposed to adjust and detect Tv of vitrimers based on the upper vitrimers doped with SiO2nanoparticles and the lower photonic crystals (PCs) from SiO2 nanoparticles. When the photonic coatings are heated, the upper vitrimers are changed from viscoelastic-solid state to viscoelastic-liquid state, intensities of reflection peaks of PCs are increased because light would easily penetrate the coatings. Tv of vitrimers could be decided according to great changes of intensities. When photonic coatings are synthesized at 140 °C for 6 h under 2.6 MPa, the lower PCs are kept the same, as doping amounts of SiO2 nanoparticles of the upper vitrimers are increased, Tvof photonic coatings are decreased from 90 °C to 72.5 °C. They have potential applications in adjustment and detection of Tv of other vitrimers, anti-counterfeiting and displays.
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