Stability and Temporal Decay of Nanopatterned Tribocharge on Nanotextured Soft Polymeric Surfaces

The contact between two surfaces is well known to induce triboelectric charge generation. We have recently examined the demolding of soft polymeric nanotextured surfaces from their master molds and found that the demolding process generates novel nanopatterned tribocharges. For such tribocharges to be useful for scientific and practical purposes, the tribocharges must be stable over long periods of time, with their stability and temporal behavior quantitatively characterized and studied. This is a highly challenging task as it requires long-term, repeated probing of the tribocharge at the nanoscale spatial resolution. In this work, we performed such a comprehensive experimental study of nanopatterned tribocharges on elastomer surfaces using Kelvin probe force microscopy (KPFM) and electrostatic force microscopy (EFM). Curve-fitting analysis of the KPFM results affirmed the temporally decaying nature of the tribocharge but also separated them into two distinct, fast and slowly decaying, components that could be attributed to two different tribocharging mechanisms. Through optimization of the curve-fitting parameters and comparison studies, we could attribute the fast and slow decay components to the tribocharges generated by tangential sliding and surface-normal separation of the material interface, respectively. The analysis also enabled us to estimate time-invariant “pedestal” potentials from the KPFM results and predict the existence of long-term stable tribocharge on the nanotextured elastomer surface. We experimentally confirmed it by re-scanning the specimens 14 days after the initial measurements. The observations, analysis, and the mechano-triboelectric charging model will benefit researchers of nanoscale tribocharges but also those interested in the study and applications of triboelectricity in general. It provides a pathway for enhancing tribo-electric energy generation.<br/>Supported by NSF grant CMMI-170648