A generation mechanism of triboelectricity due to the reaction of mechanoradicals with mechanoions which are produced by mechanical fracture of solid polymer

Mechanical fracture of solid polymer under vacuum at 77K can, in principle, produce both mechanoradicals and mechanoanions which are formed by homolytic and heterolytic scission of carbon-carbon bonds in the polymer main chain. The production of mechanoanions was claimed by a detection of tetracyanoethylene (TCNE) anion radical (TCNE^–), which was observed by electron spin resonance (ESR) spectroscopy using the electron trapping method with TCNE.A novel mechanism for generating triboelectricity is proposed. The charge carrer is an electron. The electron donor is the mechanoanion A^–, which is produced by heterolytic carbon-carbon bond scission of the main chain of polymer A. The electron acceptor is the mechanoradical B·, which is produced by homolytic carbon-carbon bond scission of the main chain of polymer B. Charge separation is due to an electron transfer from the mechanoanion to the mechanoradical when in contact. It is possible to speculate the sign of the charge induced by friction from the electron release potential of A^–, Pr(A^–), and the molecular electron affinity of B·, Ea(B·). The triboelectric series deduced from our mechanism is PMMA-PP-PE-PVDF-PTFE, in which polymers having a relatively low Pr(A^–) to high Pr(A^–) or polymers having a relatively low Ea(B·) to high Ea(B·) are arranged. This order is identical with well-known triboelectric series.Dedicated to Professor Hans-Henning Kausch on the occasion of his 60th birthday