The energy distribution of trapped charges in polymers based on isothermal surface potential decay model

Abstract

Space charge formation in polymeric materials can cause some serious concern in real operation, because it has significant influence on the performance of polymers. For example, space charge in some insulating materials can severely distort the electric field, even lead to materials degradation. On the contrary, in the case of its applications, space charge stored in electrets can greatly improve their properties. It is therefore important to understand trapped charge distribution in materials as it is considered to be a novel indicator for effective evaluation of aging status and electric withstanding strength of insulating materials. In this paper, a model based on isothermal surface potential decay (ISPD) is proposed to study the distribution of trapped charges by considering the physical mechanism of the detrapping process. By measuring the ISPD characteristics of polymeric materials and fitting the data according to the assumption of shallow and deep traps, the distribution of trapped charges is obtained, which may be related to the change of aggregation structure of polymers. In order to verify the model, it is used to analyze different ISPD decay curves of polypropylene (PP) and low density polyethylene (LDPE), as well as the ISPD data of PP electrets with/without pressure expanding treatment. The results show that the proposed ISPD model is effective and convenient. Two peaks are observed on the curve of the trapped charge density versus the trap level. The obtained distribution of the trapped charges in polymers can reveal the different nature of electron/hole traps and the different transportation behavior of hole/electron carriers, i.e., the electron-type traps show an inter-chain character while the character of hole-type traps is intra-chain. In addition, the distribution of trapped charge is further related to aggregation structure of PP and LDPE, as well as PP electrets with/without pressure expanding treatment.Index Terms -Space charge, isothermal surface potential decay (ISPD), trapped charge density, aggregation structure.

Accelerated Charge Dissipation by Gas-Phase Fluorination on Nomex Paper

“…Isothermal surface potential decay (ISPD) model was utilized to characterize the trap energy and distribution of the samples. Based on the ISPD model, the trap energy level E t and trap density N(E t ) can be calculated as [28],…”

“…Both the positive and negative surface potential decay rate of all the fluorinated samples were faster than the original samples, indicating that gas-phase fluorination had excellent suppression effect of surface charge accumulation in oil-impregnated Nomex paper. To further understand the influence of gas-phase fluorination on the surface potential decay and surface trap characteristics of oil-impregnated Nomex paper, the hole and electron trap distribution with different fluorination duration were obtained by isothermal surface potential decay method, and the trap density and energy level of shallow and deep trap are fitted with double exponential functions based on the double trap model [28]. The obtained hole and electron trap distribution of F0, F15, F30 and F45 samples are shown in Figures 5 and 6, respectively.…”

“…The obtained hole and electron trap distribution of F0, F15, F30 and F45 samples are shown in Figures 5 and 6 It can be observed in Figures 5 and 6 that all of the trap moved toward to a lower energy band after fluorination. The shallow trap density and energy level showed a similar change in both electron and hole trap with fluorination duration extended: The shallow trap energy level decreased and trap density increased when the fluorination duration was prolonged from 0 to 30 min, and then To further understand the influence of gas-phase fluorination on the surface potential decay and surface trap characteristics of oil-impregnated Nomex paper, the hole and electron trap distribution with different fluorination duration were obtained by isothermal surface potential decay method, and the trap density and energy level of shallow and deep trap are fitted with double exponential functions based on the double trap model [28]. The obtained hole and electron trap distribution of F0, F15, F30 and F45 samples are shown in Figures 5 and 6 It can be observed in Figures 5 and 6 that all of the trap moved toward to a lower energy band after fluorination.…”

Investigation on the digital image correlation and charge trap characteristics of Al/epoxy nanocomposites

“…The decay rate of the different nanocomposite materials under +DC and -DC is shown in table 3. Further, the density of trapped charge carriers N(E) in a specimen at different energy levels (E) is analysed to acquire a better perspective of how strongly the injected charge carriers trapped in the localized surface states exist in the nanocomposite material [33]. The density of trapped charges (N(E)) at different energy levels (E) within the bulk of the material with the variation of trap depth (ΔE) [34,35] is expressed by the following equation: amount of energy required for a charge carrier to get liberated from the localized trap site [20].…”

Determination of Volume Conductivity of Polyethylene Using Positive Corona, When the Current through the Sample Depends Linearly on Grid Potential

“…To simplify the analysis, it was assumed that surface trap states are uniformly distributed, in a thin layer [10]. Consequently, the surface density of charges embedded, and the potential ( ) 0, V t that they cause will be considered uniform [5] [11] [12].…”