Effects of surface fluorination on dielectric properties and surface charge behavior of water absorbed polyimide film

Abstract

With the advantages of excellent physical, chemical and thermal properties, polyimide (PI) film has been widely used as insulation material in electrical and mechanical equipment. However, PI presents water absorption capacity because of the existence of carbonyl and amine groups in the molecular chain. When exposed in moisture conditions, PI film will be degraded. Therefore, the dielectric breakdown occurs and irremediable damage will appear in insulation system. The dielectric properties of PI film are largely influenced by the absorbed water and humidity. Direct fluorination is an effective method of surface modification which can improve the properties of original material from many respects, such as the wettability, barrier properties and chemical stability. In this paper, to study effects of fluorination on dielectric properties of moistened PI films, the PI specimens were surface fluorinated for 15, 30, 45 and 60 min respectively. The specimens without fluorination were also prepared for the contrast. Then the specimens were immersed in high purity water for 6, 12 and 24 hours. The water absorption, permittivity and breakdown strength under different fluorination and immersion time were measured. Meanwhile, given that the existence of surface charge had a critical influence on the breakdown characteristics, the corona charging tests were conducted at room temperature and the charge dissipation was investigated. Obtained results show that fluorination can reduce the water intake capacity and enhance the breakdown strength of PI in moisture conditions. The decay process of surface charge and the change of detrapping charges in PI films are affected by both the fluorination and the immersion time.

Direct Fluorination as Method of Improvement of Operational Properties of Polymeric Materials

“…Optimization of the wetting ability of polymer surfaces by fluorination is promising for use in offset printing [30,40,41], ensuring the protective properties of polymer materials [29,[42][43][44][45][46], membrane [27,47]; and sorbents [38] performance. Direct fluorination of polymers also results in the formation of deep and shallow charge traps on a surface that improves dielectric [48][49][50][51], piezoelectric [52,53] properties, surface conductivity [54,55], breakdown [48,56], and DC flashover [57][58][59][60][61][62] voltages.…”

Steady-State Conduction Current Performance for Multilayer Polyimide/SiO2 Films

“…By analyzing these, we can observe an increase in conduction current in the case of fillers added in the polyimide matrix at low temperature, but we observe a conduction current decrease for nanocomposite samples at high temperature. All the films expose the same trend of conduction current profile at low electric fields (<16 kV/mm), in which the conductivity of single-layer PI/SiO 2 and fluorinated samples (FPI) is higher than the pure PI and multilayer PI-PI/SiO 2 films at low electric fields [ 47 , 48 , 49 ]. Higher conductivity can help to release trap charges [ 48 , 50 , 51 ].…”

“…All the films expose the same trend of conduction current profile at low electric fields (<16 kV/mm), in which the conductivity of single-layer PI/SiO 2 and fluorinated samples (FPI) is higher than the pure PI and multilayer PI-PI/SiO 2 films at low electric fields [ 47 , 48 , 49 ]. Higher conductivity can help to release trap charges [ 48 , 50 , 51 ]. As shown in Figure 6 , we observed that the films have at least two to three types of conduction from the slope of the current density J, relying on the applied electric field and temperatures.…”

“…For the studied conduction current of samples (films), the J vs. in Figure 6a-c. By analyzing these, we can observe an increase in co the case of fillers added in the polyimide matrix at low temperatur conduction current decrease for nanocomposite samples at high temp expose the same trend of conduction current profile at low electric fie which the conductivity of single-layer PI/SiO2 and fluorinated sample the pure PI and multilayer PI-PI/SiO2 films at low electric fields [47tivity can help to release trap charges [48,50,51]. As shown in Figure the films have at least two to three types of conduction from the slop sity J, relying on the applied electric field and temperatures.…”

Enhancement of surface insulation properties of alumina/epoxy composites through ZrO2 film sprayed by plasma atomization

“…[5][6][7][8][9] Preceding theoretical researches showed that surface morphology and chemical element of insulating materials can affect the motion characteristics of surface charges, and then influence the flashover. [10][11][12][13] At present, methods for surface modification of polymers including surface group modification, surface fluorination, oxide film surface deposition, changing the surface morphology of materials, and organic coating synthesis. The surface group modification means variation of physical and chemical properties for polymer surface through introducing functional groups.…”