New materials improve colour of reflective coatings

That bright, reflective coatings used on road signs, bicycles and clothing are important safety measures at night. They help drivers get to their destinations while avoiding bicyclists and pedestrians in low-light conditions.

Colours can fade over time

Retroreflective materials, including some tapes and road paints, work by bouncing light back toward the original source, such as a car’s headlights, making them bright and easy to see. Existing retroreflectors are usually made with glass microbeads and microprisms. Dyes, pigments or plastic layers are often added for colour; however, they tend to reduce the reflection of light, and the colours can fade over time. Hongta Yang and colleagues turned to the compound eyes of insects for a new way to address these limitations.

Material could be applied to buildings

The researchers evenly coated an array of glass microspheres with smaller balls of silica. The result is a brilliantly coloured, retroreflective material. The colour can be adjusted by changing the size of the silica crystals, and brightness can be boosted by adding layers. At 250 nanometers and 40 layers deep, the crystals appeared bright green and reflected more light than commercial coatings with no colour. In addition to boosting the brightness of objects for safety reasons, researchers say that by reflecting rather than absorbing light, the material could be applied to buildings to reduce the urban heat-island effect.

The study is published in: Langmuir 32, 2016.