Charge distribution and conduction characteristics of 2-vinylpyridine-grafted polyethylenes

Abstract

This article describes electrical properties such as space charge distribution and electrical conduction characteristics of 2-vinylpyridine (VP) grafted low density polyethylenes (PE). The VP incorporated onto PE chains changes electrical properties of PE. For example, the homocharge found in virgin PE decreases with the increase of graft ratio. As a result of the nitrogen acting as an electron donor, no space charge develops at high graft ratios. It has been found that VP reduces the current density in PE. Grafted PE with VP content of 0.754 wt % has also been found to obey a space charge limited conduction mechanism: effective charge mobility at 70 °C was calculated to be 4.6×10−16 m2/V s: an activation energy for the conduction was estimated to be 0.81 eV at 70 °C.

A General Conductivity Expression for Space-Charge-Limited Conduction in Ferroelectrics and Other Solid Dielectrics

“…(1) which can be observed experimentally (Carbone et al, 2005;Laha & Krupanidhi, 2002;Suh et al, 2000), and can be derived theoretically (Coelho, 1979) ε > 0 be both independent of the position x from the electrode where the electric current flows into the dielectric sample. The flow direction of the electric current is then given by the positive direction of x.…”

“…SCLC. Here, we have deliberately aborted the assumption of a perfectly insulating ferroelectric film, as adopted by some other schools of thought (Alpay et al, 2003;Mantese & Alpay, 2005;Okatan et al, 2010), because experimental observations of small but finite leakage currents, as well as of SCLC currents, have been widely reported in the literature for ferroelectrics and other solid dielectrics (Bouregba et al, 2003;Carbone et al, 2005;Coelho, 1979;Laha & Krupanidhi, 2002;Pope & Swemberg, 1998;Poullain et al, 2002;Suh et al, 2000) and they form a subject of their own (Pope & Swemberg, 1998). For our consideration of SCLC in compositionally graded ferroelectric films, the MottGurney law J ~ V 2 does not apply, due to the following reasons: (i) In the case of a timevarying applied voltage, there is also the presence of displacement currents so that the conduction current J , which now does not necessarily equal the total current, could be varying with position, i.e.…”

“…Space-charge-limited conduction (SCLC) in a solid dielectric occurs when free chargecarriers are injected into the dielectric sample at relatively large electric fields (Carbone et al, 2005;Coelho, 1979;Laha & Krupanidhi, 2002;Pope & Swemberg, 1998;Suh et al, 2000). For the case of SCLC in a trap-free plane-parallel dielectric capacitor (Fig.…”

“…For a current density J and an applied voltage V, the experimentally observable MottGurney law J ~ V 2 (Carbone et al, 2005;Coelho, 1979;Laha & Krupanidhi, 2002;Pope & Swemberg, 1998;Suh et al, 2000) for steady-state trap-free space-charge-limited conduction (SCLC) inside a plane-parallel dielectric capacitor is derived from three independent assumptions -(i) the presence of a single free-carrier type (i.e. injection of only p-type or ntype free charge-carriers into the dielectric), (ii) the absence of an intrinsic (Ohmic) conductivity, and (iii) the existence of a constant dielectric permittivity ε (i.e.…”

Enhanced electrical insulating properties of polyethylene by incorporating polyethylene‐g‐polystyrene graft copolymers

“…Adjusting the macromolecular chain structure by grafting is an efficient modification method. Many studies have reported the effect of functional monomers grafted onto polymers on the electrical properties of materials 34–36 . It was found that the PP‐ g ‐maleic anhydride featured improved electrical breakdown strength and markedly suppressed space charge accumulation 28 .…”