Contact charging of organic materials: Ion vs. electron transfer

In this paper we describe some of the recent literature on the contact charging (also known as tribocharging and contact electrification) of organic materials. Although it is a very familiar phenomenon, much remains to be understood about the mechanism of charging with organic materials. It has been proposed that the charging is due to the transfer of electrons and/or ions. In some studies, the correlation between the charging and the substituent constants for a substituted series of compounds has been used to support the electron transfer mechanism, and it has been proposed that the correlation reflects systematic changes in the energy levels of the highest and lowest occupied molecular orbitals of the derivatives. In others, the detection of the ions that are transferred during contact and the correspondence between their sign and that of the transferred charge have been used to support the ion transfer mechanism. In this paper, we discuss a selected number of papers that relate the charging behavior to electrochemistry and discuss the results reported in light of the two transfer mechanisms.