On the question of percolation threshold in polyvinylidene fluoride/nanocrystalline nickel composites

Abstract

The dielectric behavior of polyvinylidene fluoride (PVDF), nanocrystalline nickel (nc-Ni) composites has been investigated over a broad frequency range of 40Hz–10MHz. High effective dielectric constant (εeff=2050) and low loss (tanδ=10) at 100Hz have been observed near the percolation threshold. To the best of our knowledge, this is the highest εeff value reported to date among the PVDF based metal-polymer composites. The dielectric properties have been explained by using boundary layer capacitor effect and percolation theory while the dielectric anomalies are attributed to process of fabrication leading to thick insulating layer between the filler particles forming a gap in effective tunneling range of two filler particles and also making a difficulty in probability of higher order tunneling.

Evidence of a third kind of Johnscher’s like universal dielectric response

“…The as-purchased Ni ( -Ni) was milled for 60 h in order to obtain nanocrystalline Ni (nc-Ni) of particles size ($ 20-30 nm) confirmed from HRTEM. 5 PVDF/nc-Ni composite samples were prepared with varying volume fractions of nickel (f con ) through cold pressing and the details of sample preparation and characterizations can be found from the earlier published literatures. [4][5][6][7][8][9] The detailed method of image processing of the optical micrographs of the samples with different f con done through MATLAB software is described as follows.…”

“…20 Hence with the expectation of getting this unique type of dielectric relaxation behavior, a variety of series of PVDF/Ni composites with varying size and type of filler and varying process conditions (hot molding and cold pressing) were investigated. [4][5][6][7][8][9] Although a variety of series of PVDF/ Ni composites have been investigated, 4-9 the expected dielectric relaxation behavior was observed in the cold pressed PVDF/nanocrystalline nickel (nc-Ni) composites, which opens an interesting and novel dielectric response associated with the novel physical phenomena, which may make the material suitable for their possible electrical and electronics engineering applications.…”

“…are undergoing extensive investigations through various experimental methods. [1][2][3][4][5][6][7][8][9] Out of these methods (hot molding, cold pressing, etc. ), recent results have confirmed the importance and usefulness of the cold pressing method in case of FPD as compared to the traditional hot molding process, since cold pressing method develops better polymer dielectrics by retaining the spherulites as well as the flexibility of PVDF.…”

“…[1][2][3] Out of these polymer dielectrics, ferroelectric polymer dielectrics (FPD) have proven themselves as the emerging materials of future for electrostatic energy storage and dielectric applications, due to their higher dielectric constant, lower loss tangent and higher dielectric field strength. [1][2][3][4][5][6][7][8][9] In development of these FPD, the hit and trial combination method comprising of varieties of ferroelectric polymers (polyvinylidene fluoride (PVDF), PVDF trifluoroethylene (PVDF TrFE), etc. and varieties of fillers (metal, carbon nano tube, carbon black, graphene, etc.)…”

“…Interestingly, I also do believe that there must be a different dielectric system, completely different from the traditional fundamental systems as discussed above, which must be neither a dipolar nor a charge carrier-dominated system or must be an equally dipolar/charge carrier-dominated system and that must be at the exact boundary of the insulator to metal transition (IMT) of the polymer/metal composites (PMC). It has been found that PVDF/Ni composites have proven themselves as very good materials for energy storage [3][4][5][6][7][8][9] and electromagnetic interference shielding applications. 20 Hence with the expectation of getting this unique type of dielectric relaxation behavior, a variety of series of PVDF/Ni composites with varying size and type of filler and varying process conditions (hot molding and cold pressing) were investigated.…”