Understanding the role of the gas in the voids during corona charging of cellular electret films - a way to enhance their piezoelectricity

Abstract

The influence of the corona-charging process on the piezoelectric transducer coefficient d33 of a cellular electret film has been investigated. An increased corona voltage can be considered as a way to enhance the charge density and thus also the resulting piezoelectric effect. Higher corona-charging voltages are possible with increased ambient pressure or in suitable dielectric gases. The effect of the gas inside the voids has also been studied. Enhanced transducer coefficients were obtained by corona charging in N2 or N2O gas atmospheres at 100-450 or 100-140 kPa pressures, respectively. The highest transducer coefficients of about 790 pCN-1 were obtained when N2 gas was filled into the voids of a cellular polymer film by means of consecutive vacuum and high-pressure treatments at 295 or 313 K.

New piezoelectric composites based on isotactic polypropylene filled with silicate

“…These holes of different shapes and sizes are sometimes filled with modifier particles. Such voids are usually responsible for the accumulation of piezoelectric charge in the polymeric materials [5][6][7][8][9]11]. In most cases, a lack of wettability and adhesion is observed, which is caused by immiscibility of components.…”

Microstorms in Cellular Polymers: A Route to Soft Piezoelectric Transducer Materials with Engineered Macroscopic Dipoles

“…In a second process step after coextrusion and biaxial stretching, the size of the voids can be varied by an inflation process, based on a high-pressure treatment and a subsequent heat-setting process. [12][13][14][15][16][17][18] For the controlled inflation of the voids in the cellular polymer, the external gas pressure is usually raised and kept at a high value for a certain time (Figure 4). …”

“…Gases such as nitrogen and carbon dioxide diffuse into biaxially stretched filler-loaded polymers, [12] so that the internal pressure within the cells becomes equal to the external pressure. The polymer is inflated by a subsequent sudden release of the external gas pressure (Figure 4).…”

“…[20] The trick is the internal charging of voids by dielectric barrier microdischarges. [12,21,22] In Figure 8, the cellular polymer is represented by two electroded polymer layers, separated by an air gap. Upon application of a large electric field, dielectric breakdown is initiated in the air gap.…”

“…Investigations with different gases have confirmed that the breakdown within the voids is governed by the Paschen law. [12] There is a lot of room for improving the charging conditions of cellular polymers, by exploiting the knowledge of experts in nonequilibrium, lowtemperature, atmospheric-pressure plasma physics.…”