Ion transfer in contact electrification

Abstract

The contact charge on polymers is influenced by added organic salts, and the charge is higher when the additive is polymer-bound rather than molecular. In our studies, the presence of an ionomer consisting of a polystyrene random copolymer with pendent N-methylpyridinium toluenesulfonate groups in the host resin produces a positive charge, and the charge is higher than with the molecular analog, 4-ethyl-N-methylpyridinium toluenesulfonate. These studies were made with powders, and the charge was activated by rolling the powder with larger sized particles. The charging is attributed to ion transfer, where the toluenesulfonate anion (OTs) transfers from one particle surface to the other, and the proposal is supported by the observation of OTs on the second surface by XPS. The different charge levels were attributed to the relative mobilities of the cation and the anion, where in the ionomers, the cation is 'anchored' to the polymer and only OTs is mobile. With the molecular salt, both ions can transfer, although in unequal amounts, thus producing a smaller net charge. We now report our results from the analyses of the charged powders with a Simpson charge spectrometer, which allow us to relate the charge distributions with the charge levels in these materials.