Scientists have devised a material that perfectly aligns with the direction of a light beam, much like sunflowers following the sun.
In 2016, a study published in the journal Science explained how young sunflower plants manage to track the sun — it all has to do with circadian rhythm. According to that study, a young flower faces east at dawn, then slowly turns west as the sun moves across the sky. During the night, it slowly turns back east to begin the cycle again.
The sunflower’s turning is actually a result of different sides of the stem elongating at different times of the day. For many years, scientists have attempted to mimic sun-tracking, known as heliotropism, in artificial materials. They’ve had little success until very recently.
In a new study published this week in Nature Nanotechnology, researchers have described a new material that follows a light source. The researchers at the University of California Los Angeles, led by Ximin He, combined a photoresponsive nanomaterial (i.e. absorbs light and turns it into heat) with a thermoresponsive polymer that contracts when it encounters heat. The material was fashioned into small cylinders.
When a light source is fired on the cylinders, it gets absorbed, heating the material but only on the light-facing side. As the material contracts on the illuminated side, the cylinder bends towards the light beam. When the top of the cylinder aligns with the beam, the underside of the shaft cools down, expanding and stopping the motion of the cylinder. These cylinders respond in real-time to a light beam’s motion, continuously turning in a wide range of directions.
The authors claim that the material could improve the efficiency of light-harvesting devices. For instance, it could be employed in solar cells that always face the sun without the need for any external power input.