When two materials are brought into contact and pulled apart, a triboelectric charge generates on their surface. The triboelectric charge was first discovered more than two thousand years ago. Still, due to the sparse/stochastic distribution (only one charge on 1000 nm2 area) of charges, charge generation and retention fundamentals are still poorly understood.1 Even the primary charging mechanism is still debated whether the charge is from electrons or ions/material transfer.1,2 Another unsolved fundamental issue is how the charges sustain on the surface over a long period, even for days. Understanding the stability of triboelectric charges could extend the lifetime of charges. It is one of the challenges in air filtration, in which the filtration efficiency suffers from a gradual decrease over time due to charge dissipation. Grzybowski et al. reported triboelectric charge can co-localize with mechano-radicals generated from tribocharging.3 The surface charge destabilized and dissipated much faster once the mechano-radicals were removed from the surface. Most studies have also focused on reducing charge retention,4 but lacked discussion about how to enhance charge retention. We deposited different self-assembled monolayers (SAMs) containing stable radicals on Si wafers. The goal is to study how the layers with and without radicals affect charge retention and eventually find a way to increase the charge retention over time. Pt-coated atomic force microscopy probes brought into contact with different SAMs characterized tribocharging. The charge retention was tracked over time with Kelvin Probe Force Microscopy (KPFM) at the same location. The results show that charge dissipation significantly varies with different SAMs. Charges on hydrophilic surfaces tend to dissipate faster than those on hydrophobic surfaces, which could be explained by water vapor’s ability to dissipate the charge.

Triboelectric charge retention using self-assembled monolayers

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