A Novel Electrochromic Platform that Integrates Dielectric Elastomers and Photonic Glasses

Electrochromic materials can change colors upon a voltage, which are based on either pigmentary or structural colors. The color changes of pigments originate from changes of absorption bandgap due to electrochromic redox reactions, while the structural color changes are caused by voltage-driven rearrangements of colloidal particles. So far, both types of electrochromic materials involve currents running through the materials and side electrochromic reactions, which limits cycling and performance lifetime. To address this issue, we develop all solid electrochromic materials by integrating dielectric elastomers and structural colors. We assemble colloidal particles in elastomers in ordered (photonic crystals) and disordered (photonic glasses) patterns to produce structural colors. With the voltages on, opposite charges accumulate on the two surfaces of elastomer composites, creating a Maxwell force to compress the elastomer without any currents running through the materials. The elastomers expand in area and shrink in thickness, leading to variations in spacing between colloidal particles and thus color changes. We achieve dramatic, rapid, and reversible color changes up to 10 Hz. The color of the photonic glass elastomer is not angle-dependent as typical photonic crystals. This avoids inhomogeneous colors when new curvatures are created with out-of-plane deformations, like wrinkling or buckling. To reduce the voltage and expand the color change range, we fabricate elastomer composites with lower modulus ( ~150 kPa) and higher stretchability (~ 250%) using lower volume fraction of silica nanoparticle and introducing a secondary aliphatic acrylate precursor into the matrix. We believe this novel electrochromic material will find wide applications in wide-angle color display, color-changing robots, military camouflage, and smart windows.