The Role of Ion Transfer in Contact Electrification

The driving force for charge transfer during contact electrification has been debated as a product of either electron transfer, ion transfer, or material transfer. While it has been demonstrated that electron transfer occurs between conducting metals through differences in work functions, the driving force for similar charge transfer in polymeric materials remains uncertain. In order to better elucidate the roles each transfer plays in contact electrification, this work specifically evaluates the role of ion transfer through controlled functionalization of ionomer brushes onto the surface of polydimethylsiloxane (PDMS) films. Through the introduction of covalently attached bound charges to a PDMS surface, a series of mobile ions, with varied ionic affinity, are introduced to the sample to evaluate how these conditions impact charge transfer. PDMS surfaces are modified through silane coupling reactions of varied chemical functionality. Charge transfer is measured during contact between the functionalized PDMS sample with a counter PDMS sample located within a faraday cup. Initial work has focused on the introduced a carboxylic acid moiety, which is a weak acid and can associate with multiple mobile ions, such as Na⁺, K⁺, and Li⁺. The charge transfer of these groups charged the counter PDMS sample positively through the transfer of mobile cations. Differences in the extent of transfer charge is attributed to how the ions interact with the bound functional group, and the subsequent mobility of the ion.