The study, published in the journal progress in science, shows that the film is a kind of structural color material, which can realize the reverse reflection of light, that is, the reflected light direction is always close to the opposite direction of the incident light. Different from the chemical colors formed by pigments and dyes, structural colors are formed by refraction, reflection or diffraction of light on the complex microstructure of the object surface, which has the advantages of environmental protection and color fastness.
The research team assembled polymer colloidal microspheres with diameters ranging from several microns to more than ten microns onto the adhesive layer of ordinary transparent tape to form a single-layer microsphere array. The research shows that when the white light beam incident from the side of the film without microsphere, it will show the reverse reflection intelligent structure color: uniform and bright reflective color can be observed from the illumination direction, and the film color will change with the observation angle and light source angle from the non illumination direction.
Road traffic signs sometimes focus on reminding drivers, and sometimes they need to remind pedestrians. This kind of intelligent reflective film can meet different needs of warning. The researchers designed two experiments to prove this. In one experiment, the researchers used the film as a road demarcation line to highlight pedestrians. Because the lighting direction of the lamp is basically the same as the driver's perspective, the lines seen by the driver do not change color, and the color is bright and uniform; the perspective of roadside pedestrians is different from the lighting direction of the lights, and the color of the lines they see flickers with the vehicle from far to near, effectively reminding pedestrians to avoid the vehicles in the rear.
In another experiment, they used the film to make traffic signs that indicated speed limits and illuminated them with white light at fixed locations nearby. This time, the driver will see the logo color change with the change of perspective, so as to be alert.
The research also shows that the membrane material is waterproof, energy-saving, and its related functions are effective between - 196 ℃ and 100 ℃ above zero.
Wu Limin, the corresponding author of the paper and professor of material science department of Fudan University, told Xinhua that the film has application value in intelligent display, traffic safety reflective facilities, anti-counterfeiting labels, structural color coating and decoration.
