Nanoparticle-Wetted Relays: Reconfigurable Surfaces for Energy Transmission Contacts

摘要

Performance and reliability of dynamic physical contacts between two solid surfaces has challenged technologists from pre-Hellenistic pulleys and Da Vinci mechanisms for transmission of mechanical energy to modern switches and relays for transmission of electrical energy, currently a $4B global industry that impacts telecom and mobile phones, automotive, aerospace and consumer products. Local oscillations in the stress, temperature and electrostatic potential during a contact cycle result in the evolution of the topology, chemistry and physical properties of the two surfaces, degrading the characteristics of the junction with service. These challenges are especially acute in ultra-fast (MHz) micro electromechanical system (MEMS) relays requiring high current, low impendence operation over billions of cycles. Various surface modification approaches, such as gold alloys and refractory coatings and self-assembled monolayers, have been unsuccessful in enabling the maintenance of these multifunctional (low adhesion, low resistivity) contracts. Taking inspiration from 1940s mercury-wetted electrical contact relays and current nanoparticle organic solutions, here we demonstrate that nobel metal nanoparticle liquids (NPLs) provide reconfigurable and replenishable surface asperities that extend the durability by 10 to 100 times without the inherent toxicity of mercury or capillarity that limits relay miniaturization. These non- volatile NPLs are made of 5-20 nm Au and Pt nanoparticles with organic coronas consisting of surface tethered ionic liquids. The nanoscopic size and corona fluidity are critical in providing sufficient electrical conductivity through nanoparticle jamming while maintaining a low contact adhesion by dynamically restoring a nanoscopic asperity texture via liquid surface migration.