Ion Transfer in Contact Electrification of Neutral Surfaces

During contact between two surfaces, a transfer of charge occurs. This charge is a product of the transfer of either electrons, ions, or small amounts of material. While electron transfer has been shown to be the main charge transfer mechanism between conducting metals, the driving force for insulating materials remains uncertain. To better understand the overall process, this work specifically evaluates the role of ion transfer. Ion transfer has been studied extensively through the use of ionomers, which are polymers that contain a fixed charge group and a mobile ion. During contact, the mobile ion transfers from the ionomer to a neutral surface, with the sign of charge transferred always corresponding to the sign of the mobile ion. There remains debate on whether charge transfer comes from ion transfer alone or if polarization between the fixed and mobile ions results in additional electron transfer between surfaces. We expand upon this research by analyzing ion transfer between neutral surfaces, where polarization cannot occur. We do this by first contacting a neutral polydimethylsiloxane (PDMS) surface with an ionomer material to transfer ions to the surface. Further contacts are made with additional neutral PDMS samples, which is repeated to make a chain of contacts with a series of neutral surfaces. We measure and evaluate how ion transfer changes as a function of contacting samples, which probes the overall mechanism of ion transfer. This work betters our understanding of contact electrification.