Abstract
Nature provides much inspiration for the design of materials capable of motion upon exposure to external stimuli, and many examples of such active systems have been created in the laboratory. However, to achieve continuous motion driven by an unchanging, constant stimulus has proven extremely challenging. Here we describe a liquid crystalline polymer film doped with a visible light responsive fluorinated azobenzene capable of continuous chaotic oscillatory motion when exposed to ambient sunlight in air. The presence of simultaneous illumination by blue and green light is necessary for the oscillating behaviour to occur, suggesting that the dynamics of continuous forward and backward switching are causing the observed effect. Our work constitutes an important step towards the realization of autonomous, persistently self-propelling machines and self-cleaning surfaces powered by sunlight.
Highlights
Nature provides much inspiration for the design of materials capable of motion upon exposure to external stimuli, and many examples of such active systems have been created in the laboratory
It remains a challenge to create actuators in a dry environment capable of autonomous oscillations, which are driven remotely by either artificial visible light or, ideally, the sun acting as the noninvasive power supply
Light-driven soft actuators that operate in solvent-free environments have been studied in organic crystals[8], inorganic crystals[9], polymer brushes[10] and liquid crystalline networks (LCNs)[11,12,13,14,15]
Summary
Nature provides much inspiration for the design of materials capable of motion upon exposure to external stimuli, and many examples of such active systems have been created in the laboratory. Correspondence and requests for materials should be addressed to Autonomous oscillations are characteristic of living systems: the heartbeat, cell cycling and biorhythms are all oscillatory events These continuous energy-driven actions do not require any switching on/off of external stimuli; rather, they are powered and regulated by chemical energy, and can sometimes be influenced by external physical cycles (circadian rhythms). It remains a challenge to create actuators in a dry environment capable of autonomous oscillations, which are driven remotely by either artificial visible light or, ideally, the sun acting as the noninvasive power supply If such autonomous systems can be realized using synthetic polymers, unprecedented, solar powered, continuously moving materials and devices should emerge, which are attractive for self-cleaning coatings and surfaces, able to actively prevent adhesion of particles and (bio)chemical in various outdoor applications, as well as solar powered soft robotics. The film displays a unique, chaotic selfoscillation when exposed to ambient, non-concentrated sunlight (or a combination of common green and blue LEDs) and requires no variation in either the source or location of illumination to maintain constant motion
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