In Situ Dynamic Study of Color-Changing in Liquid Colloidal Crystals for Electrophoretic Displays

Reflective display devices, especially for electrochromic photonic crystals (ECPCs), are of great interest to researchers due to their convenient control approach, wide color regulation range, fast response, and low power consumption. Herein, liquid colloidal crystals (LCCs) of SiO2 nanospheres were prepared through an evaporation-induced self-assembly method and used as a reflective unit for fabricating dynamic ECPC devices. The ECPC device exhibited brilliant controllable structural color across the visible spectrum under low voltages (<3.5 V). Based on the in situ ultra-small-angle X-ray scattering results and reflective spectra, regulatory rules of the dynamic ECPC device concerning a color tunable range, reflectance intensity, response speed, and cyclic performance were set up, and the relationship between slurry concentration, electrode spacing, and viewing angle was established. Furthermore, a dynamic mechanism was revealed for explaining the responsive behaviors of reflection spectra during the electrical modulation, which is significant for the development of ECPC devices in the future. Based on the parameter optimization and structure design of the dynamic ECPC device, a pressure-responsive electrochromic prototype device was constructed with rapid response, dynamic structural color, and good reversibility, which demonstrated its great potential in reflective display units and multifunctional sensors.