| Description |
This thesis focuses on exploring a hygroscopically-induced 4D-manufacturing method for the fabrication of complex, 3-dimensional (3D), multimaterial, and monolithic ionic polymer-metal composite (IPMC) actuators for applications in soft robotics. IPMCs are composed of an ion exchange polymer (ionomer) membrane sandwiched between highly conductive electrodes, typically platinum or gold. Nafion is the ionic fluoropolymer commonly used as the ionomeric membrane in IPMCs. These electroactive composites can function as actuators and sensors. Until recently, fabrication techniques for IPMCs have been limited to whatever 2D shapes can be cut or formed from a sheet of Nafion material. However, recent work demonstrates the ability to 3D print (through fused-deposition modeling) a Nafion precursor to make unique 3D shapes for the ionomeric membrane. Herein, complex 3D electroactive-polymer-based structures can be created by exploiting nonuniform hygroscopic swelling between multimaterial components. This approach to manufacturing suggests that simple devices can be 3D-printed, for example as planar structures, then subjected to hydration causing hygroscopically-induced morphing that results in more complex geometry. The overall process involves two steps: (1) dual-extrusion 3D printing of the Nafion precursor and a secondary nonactive material or 3D printing a secondary material directly onto a Nafion substrate, and (2) morphing through nonuniform hygroscopic swelling. A model of the mechanics is presented, followed by experimental results that validate the model. Example 3D-printed and activated devices are described, including an eight-legged soft crawling robot that was made by first 3D printing the body in planar form and subsequently transforming it into a standing and walking robot through hygroscopically-induced folding in water. The results demonstrate feasibility and the potential of the approach for creating unique and complex soft mechatronic and robotic devices with integrated actuation and sensing. |
