Artificial phototropism for omnidirectional tracking and harvesting of light

Abstract

Many living organisms track light sources and halt their movement when alignment is achieved. This phenomenon, known as phototropism, occurs, for example, when plants self-orient to face the sun throughout the day. Although many artificial smart materials exhibit non-directional, nastic behaviour in response to an external stimulus, no synthetic material can intrinsically detect and accurately track the direction of the stimulus, that is, exhibit tropistic behaviour. Here we report an artificial phototropic system based on nanostructured stimuli-responsive polymers that can aim and align to the incident light direction in the three-dimensions over a broad temperature range. Such adaptive reconfiguration is realized through a built-in feedback loop rooted in the photothermal and mechanical properties of the material. This system is termed a sunflower-like biomimetic omnidirectional tracker (SunBOT). We show that an array of SunBOTs can, in principle, be used in solar vapour generation devices, as it achieves up to a 400% solar energy-harvesting enhancement over non-tropistic materials at oblique illumination angles. The principle behind our SunBOTs is universal and can be extended to many responsive materials and a broad range of stimuli.

An Autonomous Soft Actuator with Light‐Driven Self‐Sustained Wavelike Oscillation for Phototactic Self‐Locomotion and Power Generation

“…Very recently, Zhao et al reported a swimmer robot based on a photosensitive hydrogel oscillator showing negative phototactic movement (away from the light source) in water driven by a laser 4. They further developed an artificial phototropic system based on hydrogels or a series of photoresponsive polymers that can autonomously aim and align in the incident light direction in three dimensions 67. In addition, Martella et al reported light‐activated nonreciprocal motion in LCNs, which can be applicable in swimming devices.…”

Light Tracking and Light Guiding Fiber Arrays by Adjusting the Location of Photoresponsive Azobenzene in Liquid Crystal Networks

“…[7] Heliotropismlike actuators have been developed to achieve light tracking in artificial fiber arrays based on a feedback loop involving photothermal effects and the mechanical properties of the polymers employed. [8] A photo active light guiding actuator has been constructed to drive photo thermal deformations. [9] For photothermal actuation, a specific chromophore is often added to the system so that when illuminated with the proper wavelength, a mechanical response is generated.…”

Chemothermally Driven Out‐of‐Equilibrium Materials for Macroscopic Motion

“…[5] Recently, there is a growing interest in developing synthetic out-of-equilibrium systems to mimic biology. [6,7] Synthetic outof-equilibrium materials have been reported that employ light, [8][9][10][11] current, [12] or heat to fuel characteristic dissipative behavior. [13] Biological out-of-equilibrium systems ubiquitously use chemical fuels, such as ATP and GTP, to sustain the dissipative processes.…”