Colloidal crystals: A suitable tool for the development of nanoscale responsive structures

In this work, we report on a colloidal composite system based on polystyrene nanoparticles embedded in an elastomeric matrix able to change its color in presence of different solvents and their mixtures. The structure presents an iridescent green color that can be attributed to the ordered assembly of the constituting nanoparticles causing the formation of a pseudo band gap. The composites realized present a colorimetric variation in their response, since a remarkable blue-shift of the diffraction peak is observed. The selectivity and sensitivity of the responsive system have been investigated by monitoring the static and dynamic reflectance spectra considering different solvents and a mixture of tert-butyl alcohol and water. An analytical model has been proposed and validated in order to assess the optical chromatic response, investigating the variation in frequency of the diffraction peak as well as the filling factor. The prepared structure and the interrogation approach can be seen as a suitable tool for the development of low cost portable and visual sensors for homologues and mixtures.