Polarizing mechanism of colloidal metal particles formation in polymer electrets

Thermal treatment of polymers in electric fields induces changes in their structure and physico-mechanical properties. Noticeable variations are observed at considerable values of the field intensity (about hundreds of kV/cm), namely dipolar polarization of the polymer, increased number and dimensions of ordered areas. Modification of polymer structure under the applied electric field could be an outcome of not only dipolar polarization alone but also charge carrier injection from the electrodes. As for, for example, a gradual transfer of α-form into β-form proceeds in polyvinylidene fluoride (PVDF) in the field of injected charge due to the bulk charge relaxation. The mentioned phenomena are most peculiar to metal-polymer electrets (MPE) formed by thermal treatment of polymers between electrodes of unlike metals. Polarization in MPE is accompanied by diffusion of atoms and ions of electrode metal into the polymer, being the process of mainly electrochemical nature. Charge injection can be intensified at low field voltage by increasing the actual contact area between the electrode and dielectric. The method makes it possible to control charge density and its distribution across electret thickness. Promising is the employment of liquid-metal electrodes aimed at increasing contact area between electrode and polarized polymer. In this case one is able to observe charge injection into the polymer together with metal diffusion from the electrode into the polymer layer bulk. This work aimed to investigate polarisation effect on metal diffusion and formation of colloidal metal particles in polymer electrets