Corona charging of polymers: recent advances on constant current charging

Abstract

This paper contains a brief overview on the recent developments of corona charging of polymers, with emphasis on the constant current corona triode. This latter method, which has been successfully applied to several types of polymer, is a legacy from Prof. Bernhard Gross' work in São Carlos, Brazil. Following a short introduction to corona charging, the experimental setups are described, especially with regard to the advantages in the constant current method. A few examples are given of the use of the constant current corona triode in the investigation of electrical properties of nonpolar and ferroelectric polymers. The application of corona charging to pole nonlinear optic NLO polymers is discussed, including the perspectives for the constant current c harging method for the NLO eld. I IntroductionInterest in corona charging of dielectrics arose in the 1940s following Carlson's invention of the rst electrophotographic system, since sensitizing the photoconductive plate by corona discharge was proven more effective than other methods. A number of experimental arrangements have been used since then. For instance, in the corotron setup corona wires are placed above the photoconductive plate, whereas in the scorotron system a metallic grid is inserted between the corona wires and the plate, the grid being biased to a voltage that approximates the potential required for charging the plate. Both systems permit very rapid charging. From the 1960s corona discharge became extensively employed for charging polymer foils for electret production and also for investigating charge stability in these electrets. Corona systems for such purposes may b e simply a two-electrode arrangement comprising a point or wire and a plate or cylinder. Prof. Bernhard Gross realized, however, that invaluable information was lost during the charging process. In the 1970s he then instituted a project for developing corona triodes in which in addition to good charging control, the charging current and sample surface potential could be measured. Several versions of the corona triodes were developed, where the greatest advance was achieved when the constant current method was introduced. With this new technique, not only charging uniformity could be substantially improved but also interpretation of experimental results on charging transport was facilitated because one important parameter, the charging current, was xed. The constant current method was itself improved over the years, especially with regard to making it as versatile as possible in terms of the range of charging currents and nal charging potentials available and the accuracy in the surface potential measurement. In this paper we shall describe the most recent advances in the constant current corona triode method, and its use for charging and investigating the electrical properties of a variety of polymers. In Section 4.1, experimental results and theoretical models will be discussed

Chromofore Poling in Thin Films of Organic Glasses. 1. Overview of Corona Discharge Application

“…Temperature variations at poling affect the corona onset voltage, ion mobility, and, as a result, the V gap responsible for inaccuracies of the value of sample surface potential measured by this method. Versions of constant current corona triode poling setups [29][30][31][32][33][34][35][36][37] have been used in studies of polymer orientation, and their possible usage for poling NLO and HGP samples is still being examined [38,39]. As far as we know, the first system for measuring potential difference across a thin insulating film during the corona discharge has been reported by Weinberg [40].…”

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

“…The positive ions that arrive at the surface of the sample, transfer their charge to it, introducing potential gradients on the surface and in the bulk of the sample. Thus, a part of the charges are transported along the surface and the other part are transported through the bulk, producing an electric field in the bulk of the sample [7] [8].…”

Characterisation and optimisation of the d 33 coefficient of cellular PP films

“…This produces gas breakdown inside the voids of the foam which leave an internal surface charge on both upper and lower sides of the void with opposite polarities. The electrostatic charge creates an internal micro dipole which has the same effect as the internal dipoles of crystalline piezoelectrica materials [3]. They are also called ferro electric materials.…”