Robust Joule-heating induced transmittance modulation of CNT-sheet-paraffin based smart window

Abstract

Intelligent window with transmittance change has enabled significant advantages for the smart building. Moreover, such a window with the user’s control to ensure privacy could be obtained by the electrical power. Thanks to the horizontally aligned carbon nanotube (CNT)-sheet-like-film from drawable CNT forest, the CNT-sheet was employed as the Joule-heating induced transparent heater to modulate the transmittance change of paraffin corresponding to its solid to liquid phase change. A facile approach was used to fabricate the sandwich-like smart window cell from the CNT-sheet-paraffin nanocomposite. CNT-sheet from the CNT forest was transferred on the glass substrate and then densified by ethanol. Optical microscopy, scanning electron microscopy (SEM), and infrared (IR) thermal mapping microscopy were carried out to characterize the uniformity of the aligned-CNT-sheet. Significantly, the IR microscopy results showed its homogenous Joule-heating generation without any hot spot. The sandwich cell was made from the CNT-coated substrates and was infiltrated by the melted paraffin in between the substrates. UV–vis spectra with electrical power DC application were used to measure such smart window structures. The results showed the Joule-heating induced uniform heat generator of CNT sheet driving the solid to liquid phase change of paraffin, increasing the transmittance of the intelligent window cell six times in the visible light range. Those results have shown promise for developing the facile smart window, especially for the curve window of vehicles.