Multistimuli-responsive smart windows based on paraffin-polymer composites

[Display omitted] •Paraffin-polymer composites show ample thermal modulation of light transparency.•Photothermal and electrothermal control of sunlight transmittance is also possible.•Transparent-to-opaque transition can occur abruptly or gradually over temperature.•Efficient regulation of solar heating achieved for different weather conditions.•Low cost, facile fabrication, high photostability and flexibility. Despite their potential to reduce energy consumption in buildings and increase user's comfort, the general application of smart windows is currently hampered by economic and technological factors. To overcome these limitations, herein we report a new strategy for the fabrication of thermoresponsive smart windows based on polymer films loaded with paraffin nanoparticles. Proper selection of these components allows refractive index matching when the paraffin nanoparticles are in their solid state - i.e., high visible and near-infrared light transparency -, which is lost after melting, thereby resulting in pronounced light scattering - i.e., opacity. As a result, these films show ample modulation of sunlight transmittance upon heating, while additionally exhibiting other advantageous features: facile preparation from low-cost materials; high photostability, flexibility and scalability; and fine tunability of their thermal response. Moreover, by deposition onto transparent electrodes or incorporation of nanostructured photothermal agents, the solar transmittance modulation of our paraffin-polymer composites can also be triggered with low voltages - i.e., to warrant user's control - or sunlight absorption - i.e., to improve self-adaptation to ambient conditions. Actually, films with combined thermal and photothermal activity allow high sunlight transmission in cold weather while efficiently reducing solar heat gain indoors in sunny hot days.