(200p) Smart Windows Enabled By Buckling Instabilities in Periodic Composite Films

Smart windows that can regulate the transmission of some (or all) wavelengths of light by changing between a translucent and a transparent state can greatly reduce the costs on heating, cooling, and daylighting, highly promising for next-generation net-zero energy buildings. Unfortunately, almost all state-of-the-art smart windows require expensive transparent conductors to operate and they suffer from relatively low light transmittance in the transparent states, impeding their overall costs and energy efficiencies. Here report a novel smart window technology that eliminates expensive transparent conductors in the final devices and enables high optical transmittance in the transparent state (with performance close to traditional window glass). Self-assembled colloidal crystals are assembled using a scalable electrostatics-assisted Langmuir-Blodgett technology, followed by embedding in elastic polymers to create bilayer elastomeric composites comprising rigid skin layers with well-controlled thicknesses (determined by the sizes of the colloids). Buckling instabilities induced by bending the bilayer composites lead to strong light scattering that significantly reduces light transmittance, rendering dynamic light regulation between highly transparent and translucent states. Optical modeling and mechanical finite element analysis have also been conducted to complement the systematic experimental studies. Ultimately, the experimental and theoretical results match reasonably well.