MEAM Ph.D. Thesis Defense: “Contacts with Dynamically Tunable Adhesion and Friction via Active Materials with Thermally Modulated Stiffness”

Contact interactions, including adhesion and friction, are critical to the design of many engineered systems. Currently, most systems rely on materials with static mechanical properties, requiring careful selection of materials to realize effective systems for specialized tasks. However, with advances in smart materials, system design is no longer limited to materials with static properties. There is a significant potential to exploit active materials for dynamic control of mechanical behaviors, including adhesion and friction, to enable the design of systems with improved performance and new functionalities. Example applications of such systems include the gripping and manipulation of objects in robotics and manufacturing, the temporary attachment of wearable devices, and the creation of tactile interfaces for virtual reality. In this work, active control of adhesion and friction is realized using materials with tunable stiffness. In particular, thermally responsive polymers, which exhibit substantial changes in stiffness, provide significant potential for adhesion and friction control. We demonstrate the use of a conductive thermoplastic and a shape memory polymer, both with thermally modulated stiffness, to dynamically tune adhesion and friction. Through a combination of experimentation and finite element analysis, we present a composite microstructured adhesive with high strength and adhesion switchability, while highlighting the role of scale in achieving fast response times. Through further experimentation, we investigate the ability to tune friction, using stiffness modulation to enable a transition from Coulomb friction to adhesion-dominated friction. This ability to dynamically control adhesion and friction offers new opportunities for the design of engineered systems.