A material that can perfectly align with the direction of a light beam is reported this week in Nature Nanotechnology. This material, formed into small cylindrical stem-like shapes, is able to follow a beam of light - much like sunflowers do in the Sun.
Widely observed in nature, phototropism is when organisms follow a light source for foraging or reproductive purposes. However, artificial phototropism has been challenging to achieve as it is difficult to find the right balance between the material composition and its properties.
Ximin He and colleagues combined a photoresponsive nanomaterial that can absorb light efficiently and transform it into heat with a thermoresponsive polymer that contracts when heated. The authors then shaped the resulting material into small cylinders. When illuminated, the cylinder absorbs light and becomes hotter, but only on the side facing the light source. As the material contracts on the illuminated side, the cylinder bends towards the light beam. Once the top of the cylinder aligns with the beam, the underside of the shaft, now in the shadow of the light, cools down, expands and stops the motion of the cylinder. These cylinders can follow a light beam continuously in a wide range of directions.
The authors suggest this research could be used to improve the efficiency of light-harvesting materials, as the cylinders bend autonomously to expose the tip to the maximum amount of light.
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