Interfaces: nanometric dielectrics

Lewis, T. J.

doi:10.1088/0022-3727/38/2/004

Cited by 441 publications

(291 citation statements)

References 51 publications

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“…Indeed, thanks to the presence of the nanofiller/polymer interfaces [5][6][7][8][9], such material systems have been envisioned as an answer to many high voltage insulation problems [10]. For example, the partial discharge resistance, electrical treeing growth, space charge formation and dielectric breakdown performance of nanodielectrics have been compared with the respective unfilled and microfilled counterparts and worthwhile improvements in such properties have been reported [11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Polyethylene/silica nanocomposites: absorption current and the interpretation of SCLC

Lau

Vaughan

Chen

et al. 2016

J. Phys. D: Appl. Phys.

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The topic of nanodielectrics continues to receive significant attention from today's dielectrics community, due to the property enhancements that can stem from the unique interfacial features within such material systems. Nevertheless, understanding of the interfacial phenomena that occur in nanodielectrics and which determine their electrical behaviour is challenging. In this paper, we report on an investigation into the absorption current behaviour of two nanocomposite systems, one containing an untreated nanosilica and the other containing the same nanofiller chemically modified using trimethoxy(propyl)silane.The results indicate that the absorption current behaviour of all the nanocomposites is very different from that of the reference, unfilled polymer; while the current flowing through the unfilled polyethylene decreased monotonically with time in a conventional manner, all nanocomposites revealed an initial decrease followed by a period in which the current increased with increasing time of electric field application. Possible mechanisms leading to the observed absorption current behaviour in the nanocomposites are discussed with the aid of space charge measurements. The presence of space charge limited conduction (SCLC) and its trap-filled limit is proposed.Keywords: nanocomposites, nanosilica, interface, absorption current, space charge limited conduction. 2 IntroductionThe addition of a nanofiller to a polymer matrix has been shown to be a flexible means of tailoring the dielectric properties of materials [1][2][3] and Chen et al. [19], for example, have emphasized the unsatisfactory nature of our understanding of charge transport mechanisms. In conventional polymeric insulation, charge transport mechanisms are extremely complicated, when compared with many conducting and semiconducting materials [20,21]. In semicrystalline polyethylene, for example, chainfolded lamellar crystals are surrounded by amorphous conformations and there is likely to be a high concentration of traps relating to each of these structural motifs. On the addition of a nanofiller, charge transport mechanisms will become yet more complicated, since the inclusion of nanoparticles will introduce extensive interfacial surfaces between the nanofiller and the polymer. The presence of such interfaces may directly introduce additional nanofiller/polymer trapping sites and/or modify the surrounding polymer morphology, thereby affecting the local density of states within the system.The current flow caused by the action of an applied electric field on charge carriers within a dielectric material can broadly be categorized into three types [22]: the initial current that flows through the material is the capacitive charging current, which causes a dramatic rise at the very beginning of the voltage application. This is followed by a gradual decrease of current, known as the absorption current or the anomalous current. Conventionally, the absorption current decreases slowly until it reaches a quasi-steady state, providing a conduction c...

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Section: Introductionmentioning

confidence: 99%

Polyethylene/silica nanocomposites: absorption current and the interpretation of SCLC

Lau

Vaughan

Chen

et al. 2016

J. Phys. D: Appl. Phys.

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“…Consequently, this study was undertaken to investigate the effect of an MMT clay on properties and structural evolution in a model polyethylene. Since the importance of interfaces in nanodielelectrics is well recognized (3)(10)- (12) , a principal objective concerned the interactions that occur between the polymer and the nanofiller. Following the pioneering ideas of Lewis (10) , Tanaka (13) has proposed a concentric shell model in which interactions can be thought of as occurring at a range of dimensional levels.…”

Section: Introductionmentioning

confidence: 99%

Polyethylene Nanodielectrics: The Influence of Nanoclays on Structure Formation and Dielectric Breakdown

2006

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Polymeric composites containing nanometric fillers have attracted considerable interest because of the attractive properties that such materials can display. In the area of nanodielectrics, many workers have stressed the significance of the interfaces that exist between such fillers and the host polymer as being critical in influencing properties. Indeed, Tanaka (1) proposed a concentric shell model in which interactions can be thought of as occurring at a range of dimensional levels; Nelson and Fothergill (2) considered nanodielectrics in terms of an interaction zone. In this work, we set out to prepare a range of nanocomposites based on polyethylene (PE) and montmorillonite nanoclay (MMT), to examine the effect of MMT dispersion on properties and structure formation and, thereby, to explore both short-range molecular effects and the extent of the polymer/nanoclay interaction zone. Figure 1 compares AC ramp breakdown results obtained from 3 materials at a ramp rate of 50 V s -1 . Where dispersion of the MMT is poor (C Quenched), the breakdown strength is greatly reduced compared with a comparable system containing well-dispersed nanoclay (E Quenched). This is in line with behaviour reported for nano-and microcomposites (2) , suggesting that it is attributable to aggregation of the MMT in C. However, attempts to improve the breakdown strength of E by controlled crystallization were unsuccessful; systems prepared by rapid quenching from the melt or by prolonged isothermal crystallization both behaved in an equivalent manner. This is in contrast to the same polymer, but without MMT (B 117 o C), where controlled crystallization can lead to improved properties, as reported elsewhere (3) . Thus, when quenched, equivalent polyethylene materials with and without MMT exhibit similar breakdown behaviour, provided the MMT is well dispersed. However, in the absence of MMT, isothermal crystallization can result in improved performance whereas, when MMT is present, this appears not to occur.To explore the origin of the above effects, the influence of MMT on structural evolution in PE was examined. In the scanning electron microscope (SEM), all the materials where MMT was absent or poorly dispersed were found to exhibit spherulitic morphologies. In contrast, Fig.2 shows a sample of Material E, which contains 5% by weight MMT, following crystallization at 117 o C. An MMT aggregate ~1 µm in size can be seen near the centre of this image but, elsewhere, it is not possible to distinguish MMT platelets from polymer lamellae. Although the material is highly nucleated, the lamellar texture also appears highly disrupted. Thus, in the absence of MMT or when the MMT is poorly dispersed, crystallization of the polymer leads to conventional morphologies, whereas well-dispersed MMT appears to promote nucleation but, subsequently, to disrupt the processes by which ordered structures form. This interpretation of fig.2 is supported by quantitative studies of crystallization kinetics and the thermodynamics of crystallization. MMT increases...

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“…Similarly comparing the Equation (8) divided by Y as considered by [5] with Equation (12), an overestimation of 137% has been observed.…”

Section: Shear Stressesmentioning

confidence: 87%

“…However the researchers [5] [7] [12] have indicated the opposite characteristic of Equations (8) and (9).…”

Section: Coupling Of Dielectric and Elastic Response Parametersmentioning

confidence: 99%

Measurement of Error in Electrostriction Based Dielectrics

Singh¹

2014

OALib

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While correlating the various components of mechanical stress tensor due to elastic response with the corresponding components of electrically induced stress tensor pertaining to quadratic electrostriction, proper precautions are to be observed for higher order electromechanical coupling. Contributions from lateral stresses, electrical and mechanical boundary conditions are to be considered for the correct estimation of induced strain in elastic dielectrics. The knowledge of dependence of Maxwell's electrostatic stresses on dielectric constants and on the orientation of dielectric material with respect to the electric field vector is necessary for the exact estimation of electrically induced strains. The contributions from the variation in transverse components of dielectric tensor produced by the variation in lateral stresses are to be incorporated into the expression for the correct estimation of electrostrictive coefficients. The electromechanical behavior of elastic dielectric is discussed and the errors often committed in using incorrect formulae for electrostriction are reported.

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Interfaces: nanometric dielectrics

Cited by 441 publications

References 51 publications

Polyethylene/silica nanocomposites: absorption current and the interpretation of SCLC

Polyethylene/silica nanocomposites: absorption current and the interpretation of SCLC

Polyethylene Nanodielectrics: The Influence of Nanoclays on Structure Formation and Dielectric Breakdown

Measurement of Error in Electrostriction Based Dielectrics

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