Electrization and Polarization of Polymers During Friction

Aside from contact electrization, local accumulation of charges takes place as a result of mechanical separation and formation of a double electrical layer (DEL). Mechanical separation of charges is brought about by exfoliation of adhesive films from the metal or semiconducting samples. DEL may arise in response to chemical interactions of two phases or as a result of selective adsorption of similar ions, e.g. in the presence of oriented dipoles on the contact surface of one of the phases. Electrization can also be induced by the donor-acceptor (DA) interaction, since in agreement with the electrostatic theory of adhesion DEL are formed at the interface of two substances at the expense of DA links and govern the efficiency of adhesive interactions [41]. 

Electrical charges generated by static electrization scatter not only over the surface but across the material bulk as well. The direct consequence of friction-induced electrization process in polymers is the emergence of the electret state. 

According to numerous investigations at the end of the 20 century polymers acquire a triboelectret state as a result of intensive electrophysical processes during frictional interactions with a solid counterbody [47]. The 

The principal characteristics of the triboelectret state in polymers recorded experimentally are i) the efficient surface charge density (ESCD) value and ii) the thermally stimulated depolarization (TSD) current spectrum, i.e. the discharge current dependence of the electret on its heating temperature. The analysis of TSD spectra helped to estimate the parameters of the triboelectret state, including the homo- to heterocharge relation in a dielectric, activation energy of the charge relaxation processes, relaxation time and others. 

The TSD current spectra of triboelectrets of polar as well as nonpolar polymers show three peaks (Table 4.3). PE peak II is attributed to relaxation of the residual polarization as a result of accumulation and orientation 

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