PDMS-paraffin/graphene laminated films with electrothermally switchable haze

Transparent, flexible composite films with switchable haze are presented that respond stably and rapidly to applied bias. The composite film is based on the laminated structure of all flexible materials, such as the polyethylene terephthalate substrate, graphene, paraffin-polydimethylsiloxane (P-PDMS) organogel, and PDMS overlayer stacked in order. Upon applying a bias, the graphene is Joule-heated, leading a microstructural transformation of paraffin impregnated in the PDMS matrix, which in turn causes the modulation of light scattering. While the total transmittance is maintained above 90% in the visible range, transmission haze of the film can be controlled over the range from 0.5 to 85% with a low applied voltage and power consumption of 18 V and 0.33 W/cm2, respectively. Because of the presence of an over-coating layer of PDMS, stable and reliable operation of the composite film is achieved for number of switching cycles. The advent of a highly transparent optical film with haze controllability that is made possible by this work can be used as a diffusive film to enhance the light-trapping properties for photovoltaics, and attachable films with controllable clarity on a window for ensuring personal privacy.