Schematic diagram of the principle of self-oscillating "solar artificial muscle engine" based on porous film 

Recently, Chinese scientists developed a self-oscillating "solar artificial muscle actuator" based on porous films, and explored its application as an engine, only a bold imagination in the past. It pioneers a new path to efficiently use solar energy. A related paper introducing the research work was published in the world-renowned academic journal Nature Communications. 

This self-oscillating artificial muscle actuator based on porous flexible polypropylene/carbon black film was jointly designed by professors Liu Zunfeng and Chen Yongsheng of Nankai University and Associate Professor Zhou Xiang of China Pharmaceutical University. They developed a "solar artificial muscle engine" on the basis of the breakthrough of the principle. 

The researchers found that solvent evaporation in a polymer film causes volume contraction and that light illuminating one side of the film accelerates solvent evaporation inside the film, resulting in anisotropic volume contraction and phototropic bending. "Experiments have proved that the introduction of porous structure in a film can effectively promote the mass transfer of solvent molecules, causing faster bending and greater bending range of the thin film material. Therefore, we believe that photo-induced solvent evaporation based on porous films may be a good candidate to achieve self-oscillating drive," said Liu Zunfeng.

Based on this research, the research team finally designed and developed this self-oscillating driving film based on sunlight. Oscillation is mainly achieved by the alternating volume contraction on both sides of the polypropylene/carbon black polymer film caused by the photothermal-derived solvent evaporation. Anisotropic solvent evaporation and rapid gradient diffusion in polymer films maintain oscillating bending driving under the illumination of divergent light. 

It is reported that this research realizes for the first time the self-oscillating driving under the influence of divergent light including sunlight, infrared light and simulated sunlight, and also realizes the self-oscillating motion under different illuminating angles of divergent light. This photoreactive self-oscillating actuator has excellent oscillation performance (force density of 30.9 × 10^-5 J/g and power density of 15.4 × 10^-5 W/g under infrared light), excellent load capacity (load objects up to 4 times its weight) and high energy conversion efficiency (0.9%). It maintains continuous oscillation motion given a continuous supply of solvents. 

The first author of the paper is Dr. Li Jingjing. Professor Liu Zunfeng and Professor Chen Yongsheng of Nankai University, and Associate Professor Zhou Xiang of China Pharmaceutical University are the joint corresponding authors. 

Link to the paper: https://www.nature.com/articles/s41467-022-33374-x#article-comments 

(Edited and translated by Nankai News Team)