Porous PTFE space-charge electrets for piezoelectric applications

Abstract

Porous polytetrafluoroethylene (PTFE) films were positively or negatively corona charged at room or elevated temperatures. Their charge storage behavior was investigated by means of isothermal surface potential measurements in direct comparison to nominally nonporous samples of the same polymer. It was found that porosity may lead to significantly enhanced surface-charge stability for both polarities. Direct piezoelectricity was studied on quadruple, double, and single layer samples by means of quasi-static measurements. For the determination of indirect piezoelectricity, frequency-dependent acoustical-transducer experiments were carried out. Both applications-relevant measurements yielded piezoelectric d33 coefficients of up to approximately 600 pClN or 600 pmlV. These values are more than one order of magnitude higher than in conventional piezoelectric polymers such as polyvinylidenefluoride (PVDF) and almost comparable to the highest known values of inorganic piezoelectrics. Consequently, the novel piezoelectric porous-fluoropolymer spacecharge electrets exhibit an outstanding potential for various device applications that are very briefly discussed.

Fluoroethylenepropylene ferroelectrets with patterned microstructure and high, thermally stable piezoelectricity

“…Since the thermal stability of d 33 in ferroelectrets is dependent on the retention of the internal space charges, two approaches are possible to achieve this goal. One is the development of new ferroelectrets based on thermally stable electret materials, such as cross-linked PP (XPP) [10], cycloolefines (COC) [11], polyethyleneterephthalate (PET) [12], polyethylene-naphthalate (PEN) [13], and fluorocarbon polymers [14][15][16][17][18][19][20][21][22][23][24][25]; the other is chemical modification, such as surface modification of cellular PP by using fluorination [26]. Of these two approaches, the former one, in particular the one using fluorocarbon films, has shown the most promise.…”

Piezoelectric Coefficient Properties of a Flexible PZT/Upe/C Composite

“…% of carbon content the piezo-activity is reduced as shown in Fig. (1), possibly because the electrical conductivity of the composite has increased so much [8,9]. 2) shows the piezoelectric constants of PZT/UPE/C (49/50/1) as a function of poling time .It appears that a very short poling time of 7h was enough to polarize this composite while without carbon the composite require almost 24 h to be poled.…”

Fabrication of fluoropolymer piezoelectrets by using rigid template: Structure and thermal stability

“…For example, piezoelectrets with improved thermal stability were prepared from cycloolefines, 8 polyethylene-terephthalate, 9 polyethylene-naphthalate, 10 and from fluoropolymers. [11][12][13][14][15][16][17] Moreover, new methods to fabricate films with void structure are also being actively developed to further improve the piezoelectric activity.…”