Triboelectricity in polymers: effects of the ionic nature of carbon-carbon bonds in the polymer main chain on charge due to yield of mechanoanions produced by heterogeneous scission of the carbon-carbon bond by mechanical fracture

Triboelectricity of polymers is a phenomenon caused by mechanical scission of the polymer main chain on a frictional surface. A frictional experiment was designed to examine mechanical fracture of polymers in a vacuum in the dark at 77 K. The mechanical force on polyvinyl chloride (PVC) and polyvinyl fluoride (PVF) powder induced two types of scission of the carbon-carbon bonds of polymer main chains. The first was homogeneous scission of the carbon-carbon bond, which produced chain-end type neutral free radicals (called PVC and PVF mechano-radicals), which were detected by electron spin resonance (ESR) spectrometry, and the other was heterogeneous scission of carbon-carbon bonds. The mechanical force on a biased carbon-carbon bond, composed of bonding electrons biased by a substituent group or atom attached to the carbons, induced heterogeneous scission of the carbon-carbon bond, and produced macro-ionic species (called PVC and PVF mechano-anions), which were detected by ESR using an electron-trapping method with tetracyanoethylene. The yields of mechano-anions were estimated to be 50 +/- 10% for PVC and 66 +/- 9% for PVF. We employed delta chemical shift (\Deltadelta(BE)\) as the scale of deviation of the bonding electrons, i.e., the degree of ionic nature of carbon-carbon bond of the polymer main chain. The yields of mechanoanions of PVC, PVF, and several other polymers reported previously [1-5] showed logarithmic increases with increases in \Deltadelta(BE)\. According to our proposed model of triboelectricity, which was based on an electron transfer reaction from the mechano-anions as electron donors to the mechano-radicals as electron acceptors on the frictional surface, the induced charge amounts (Y-c) of polymers were estimated as 0.3-2.4 x 10(-3) C/m(2). Y-c was given as a logarithmic function of \Deltadelta(BE)\ Y-c= 1.6 x 10(-3) +4.6 x 10(-4) In (\Deltadelta(BE)\) (C) 2004 Elsevier B.V. All rights reserved.