Transparent photothermal films with high optical selectivity for anti/de-icing

A variety of transparent photothermal films with enhanced ultraviolet and near-infrared solar radiation absorption has been investigated to operate in cold environments in recent years. However, the enhancement of solar energy harvesting has to excessively sacrifice the transmittance of visible light in most existing anti-frosting and anti/de-icing systems, which leads to a widespread constraint in the applications requiring high transparency. In this study, a new type of transparent photothermal film, PMMA-iAg, was proposed and optimally designed. The polymethyl methacrylate (PMMA) is doped with indium tin oxide (ITO) nanospheres and silver nanocylinders (AgNCs). Effects of the particle doping concentration ratio and volume fraction f_v on the light transfer of the PMMA-iAg film have been systematically studied. An evaluation parameter of “deviation from the ideal spectrum” σ_T is established to assess the photothermal performance and transparency simultaneously. The results show that the present PMMA-iAg film can achieve a UV and NIR absorbance of 93% and a visible transmittance T_p of 80%. Moreover, the PMMA-iAg films can absorb more high-energy light (UV) instead of letting them transmit. In particular, the effect of ice-drops on the transmittance and haze of the transparent photothermal film was investigated at different projected surface coverage ratios f_a and wettability. The results indicate that ice-covered films with both hydrophilic and super-hydrophobic surfaces achieve outstanding transmittance. The ice-covered films with super-hydrophilic surfaces have a remarkably low haze. This work provides guidance for designing efficient transparent photothermal films for the application of anti/de-icing.