Some living organisms, such as the octopus, can swim away and alter their body color or shape for disguise and self-protection. Scientists have recently reported polymer gel systems that can mimic such synergistic color/shape changes. However, it remains a challenge to design robots that can simultaneously change shape and color and swim, like an octopus.

A team led by Wei Lu and Tao Chen, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, has developed a new class of blue fluorescent carbon dots glycol gels which can be switched to red fluorescent hydrogels upon glycol-water solvent exchange. The glycol gel layer was combined with an elastomer layer to create a two-layer soft robot.

When the actuator is placed on a water surface, glycol spontaneously diffuses out of the gel layer to allow water uptake. This leads to a color change from a blue dispersion fluorescence to a red aggregation-induced emission (AIE) and a shape change, as well as a large surface tension gradient that promotes autonomous locomotion.

 

 

The researchers constructed octopus-like, color-changing soft robots with multiple synergistic functions from these gels. Eight glycol-vinylfunctionalized carbon dots (VCDs) gel bilayer actuators formed the arms of the octopus and a single glycol-VCD gel the head. When immersed in water, the glycol-VCDs gel layers of the arms absorbed water. They bent, which was accompanied by a color change from blue to red. The glycol-VCDs gel funnel in the head “squeezed out” glycol, creating a surface tension gradient in the surrounding water that caused the octopus robot to swim in a sinuous but directional path. The synergistic process of color and shape change of the gel octopus could be reversed after immersion in glycol.

The team anticipates that the actuators could be used for environmental applications, aquatic exploration, and camouflage.

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• Aggregation Induced Emissive Carbon Dots Gels for Octopus-Inspired Shape/Color Synergistically Adjustable Actuator,
  Shuangshuang Wu, Huihui Shi, Wei Lu, Shuxin Wei, Hui Shang, Hao Liu, Muqing Si, Xiaoxia Le, Guangqiang Yin, Patrick Theato, Tao Chen,
  Angew. Chem. Int. Ed. 2021.
  https://doi.org/10.1002/anie.202107281