Frequency, temperature-dependent behavior of dielectric properties and determination of glass transition temperature of polyethylene thin film

Abstract

PE thin films of 750 nm thickness were obtained from polyethylene in the form of bulk (PE) with a molecular weight of 35000 g/mol under 10-3Torr vacuum by the thermal evaporation method. PE thin films were prepared in the form of capacitors between aluminum (Al) electrodes. Dielectric measurements of the prepared PE thin films were operated at an angular frequency of 10-106 rad/s and a temperature range of 233-373 K. When the obtained results were analyzed with the Cole-Cole model, it was seen that the dielectric constant of PE thin films was about 20 at room temperature, and three different polarization mechanisms were effective in different frequency and temperature ranges. Among these mechanisms, it was determined that α-relaxation represented the glass transition behavior. In the analysis performed using the Vogel- Fulcher-Tamman (VFT) model, it was determined that the glass transition temperature of the PE thin films was around 315 K (42). It has been observed that in the production of PE thin film by a thermal evaporation method, breakages may occur in the main chain and a transition from linear chain form to a cross-linked network form. The results obtained showed that PE can reach higher dielectric constant values in thin-film form compared to bulk form. Accordingly, it may be possible to use PE thin film in micro and nano-size energy storage systems.