Photomechanical Jumping of Liquid Crystalline Polymer Networks Soft Robots

초록

The jumping motion has been adapted by various land creatures as means to achieve daily goals, whether that is to avoid their natural enemies or overcome physical obstacles. In robotics, a key challenge has been the pursuit of on-demand and direction-controlled jumping motion that would render an agile maneuverability around large obstacles and rough terrains at low energy costs. In this study, we report untethered monolithic jumping soft robots that are operated by photomechanical snap-through. In the construction of miniaturized robots, a remote powering system is essential to avoid the undesirable weight penalty. Light-responsive molecular switches can transduce photon energy input into mechanical output that then sustains remote-powering materials. We synthesize polymeric soft robots with an azobenzene molecular switch where 270˚ super twisted nematic geometry is programed unto liquid crystalline polymer networks (LCNs). Under actinic 365 nm UV light irradiation, the perpendicular alignment of photo-responsive molecules between top and bottom of a soft robot induces bistable structures, providing efficient energy accumulation. The accumulated photoinduced energy is then instantaneously released through topological conversion (i.e. snap-through) that induces unprecedented photomechanical jumping via a prompt energy transfer to the ground. A quantitative analysis of the curvature and stress of the soft robots follows, and the experimental jumping behavior is supported by a finite element method (FEM) simulation. The jumping capability of the soft robotic LCN reaches 15.5 body length (BL) height, and 880 BL/s maximum take-off velocity. In addition, bi-directional light irradiation is employed from top and bottom in order to enable continuous jumping of the soft robotic LCNs regardless of the landing direction and curvature of the soft robots. The irradiation of patterned light breaks the symmetry of snap-through and allows direction controlled jumping behavior.