Compound electret-system with improved hydrophobicity and charge stability

Abstract

In this work, we propose a compound electret-system with improved hydrophobicity and charge stability in water and at elevated temperatures by bonding a solid fluorinated-ethylene-propylene (FEP) film to a porous polytetrafluoroethylene (PTFE) film. Two bonding approaches are investigated, the electrostatic-bonding and melting-bonding, to laminate the FEP and PTFE layers. Experimentally, the compound system shows improved hydrophobicity and charge stability both in water and elevated temperatures compared with the single layer FEP. The contact angles of the compound samples with electrostatic-bonding and melting-bonding are 139 and 124°, respectively. After immersion in water for 16 hours, surface potentials of −406 and −105 V are retained in the samples with electrostatic-bonding and melting-bonding, respectively, which exceeds the single layer FEP. The open circuit thermally stimulated discharge (TSD) current spectra show that the negatively charged electrostatic-bonding sample has a broad positive current peak at 202 °C, while for the melting-bonding sample charged under the same conditions, shows two current peaks at 231 °C and 269 °C. The enhancement of hydrophobicity and charge stability in water for compound systems must be attributed to the specific geometry on the surface of porous PTFE layer, and the improved thermal stability of charges in melting-bonding compound system could be due to the deep charge traps at the interface between FEP and porous PTFE layers generated during heat-pressing process.