  Corona charging a free-standing polymer film can produce a quasi-permanent
potential difference across the film thickness, while the absolute amplitude of
surface voltage may be highly sensitive to the free charges. To precisely
control the voltage distribution, we investigated the flow electrification
technology, by exposing corona-charged polyethylene terephthalate films to a
variety of sodium salt solutions. The surface voltage and the free charge
density were adjusted by the salt concentration, the anion size, and the flow
rate. The dipolar component of electric potential remained unchanged. This
result has significant scientific interest and technological importance to
surface treatment, filtration, energy harvesting, bio-actuation and
bio-sensing, among others.
