Robotic Materials Using Liquid Metal and Ionogel

This talk will discuss recent advances in our group on the use of liquid metals and ionogels within the context of robotics. While there are plenty of differences between these materials, they have some common features such as conductivity, mechanical extensibility, and facile processing. They are both useful for adding functionality to soft robots.<br/> <br/>Ionogels are polymeric materials swollen with ionic liquids. They are similar to hydrogels, which are polymeric networks swollen with water, yet have advantages relative to hydrogels such as gravimetric stability (due to the ionic liquid not evaporating) and electrochemical stability. These types of gels are useful for making robotic bodies because they can be deformable and easy to fabricate. Yet, gels typically have weak mechanical properties. This talk will discuss efforts in our group to make tougher ionogels using simple one step processing. In one case, we utilize phase separation to create hydrogen bonded domains within a polymer network that result in toughening. In a second case, we use the ionic liquids to crosslink the gels to give them both glassy and gel-like properties.<br/> <br/>Liquid metal refers to gallium or gallium-based alloys. These alloys of gallium are liquid below room temperature and are therefore extremely soft and flow in response to stress to retain electrical continuity under extreme deformation. I will discuss the latest efforts in our group to utilize this material within the context of robotics. One example includes printable metallic structures that can grow (get larger) in response to water. We have demonstrated that these can be useful to create circuits that change shape with time while maintaining conductivity. Liquid metals can also be utilized for performing simple tactile logic, in which the response of an elastomeric material will change depending on the way it is touched. This helps break the “sense-compute-respond” model often used to control robots by simplifying it to “sense-respond” based on the movement of elastomeric materials embedded with liquid metal. It is also possible to use liquid metal to actuate soft robots using either surface tension to exert forces on surfaces or electrochemical formation of gas to expand pneumatic chambers. Finally, more recently we have developed a way to separate the native oxide from the surface of liquid metal to print thin oxide films. To our surprise, the films are conductive and metallic-like. Thus, we can print ultra-thin (4 nm thick) transparent conductors over large surface areas at room temperature. Combined, these advances have exciting implications for soft robotic materials.