Triboelectricity in polymers: effects of the ionic nature of carbon–carbon bonds in the polymer main chain on charge due to yield of mechano-anions 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 (|ΔδBE|)” 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 mechano-anions of PVC, PVF, and several other polymers reported previously [1–5] showed logarithmic increases with increases in |ΔδBE|. 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 (Yc) of polymers were estimated as 0.3–2.4×10−3 C/m2. Yc was given as a logarithmic function of |ΔδBE|; Yc=1.6×10−3+4.6×10−4 ln (|ΔδBE|).