Optical Property Evolution of Ultrathin Porous Polymer Films after Introducing Carbon Black

Ultrathin porous polymer films with brilliant whiteness have been a research hotspot recently. It is curious about the evolution of optical properties of porous polymer films (white) after introducing carbon materials (black) with high light absorption. Will their color definitely evolve towards black? Here, ultrathin porous polymer films with brilliant whiteness, even with CB (carbon black) that absorbs visible light, are prepared from black polymer suspension by spin coating for the first time. The structure-activity relationship between their structures and optical properties is thoroughly analyzed. Further, the effects of pore size, porosity, film thickness, and CB content on the reflectance and transmittance are systematically investigated by finite-difference time-domain (FDTD) simulations. The results indicate that introducing porous structures to polymer films significantly increases their reflectance and reduces their transmittance. When CB content is low, its impact on reflectance is small or even negligible, while when it is high, it presents a negative effect. And it is negatively correlated with the transmittance. Especially, the reflectance of porous PS (Polystyrene)/CB films containing 0.001 g CB is even higher than that of pure porous PS films, which does not occur in FDTD simulations, attributed to the porous structure reinforcement from CB in actual experiments.