Enhanced breakdown strength of multilayered films fabricated by forced assembly microlayer coextrusion

Abstract

There is a need in electronic systems and pulsed power applications for capacitors with high energy density. From a material standpoint, capacitive energy density improves with increasing dielectric constant and/or breakdown strength. Current state-of-the-art polymeric capacitors are, however, limited in that their dielectric constant is low (2–4). Our approach to improve polymer film capacitors is to combine, through microlayer coextrusion, two polymers with complementary properties: one with a high breakdown strength (polycarbonate) and one with a high dielectric constant (polyvinylidene fluoride-hexafluoropropylene). As opposed to the monolith controls, multilayered films with various numbers of layers and compositions subjected to a pulsed voltage exhibit treeing patterns that hinder the breakdown process. Consequently, substantially enhanced breakdown strengths are measured in the mutilayered films. It is further shown, by varying the overall film thickness, that the charge at the tip of the needle electrode is a key parameter that controls treeing. Based on the acquired data, a breakdown mechanism is formulated to explain the increased dielectric strengths. Using the understanding gained from these systems, selection and optimization of future layered structures can be carried out to obtain additional property enhancements.

Toward Anisotropic Materials via Forced Assembly Coextrusion

“…Similar voiding has been previously imaged in multilayer films for dielectrics, resulting from crazing as the breakdown mechanism. 51 In conjunction with SEM, SAXS was conducted on the deformed multilayer films in both the ED (Supporting Information Figure S2) and TD (Supporting Information Figure S3). SAXS analysis revealed a characteristic scattering vector peak of 0.26 nm −1 .…”

Tuning the mechanical behaviour of structural elements by electric fields

“…Moreover, better dielectric layers have to be adopted to improve the mechanical quantities (shear strength, bending stiffness) of interest. To this purpose, multilayer dielectric films 21 have been identified as suitable candidates. In closing, cyclic electromechanical tests will be performed for assessing the reliability, the durability, and the fatigue behaviour of EBL's interfaces.…”

Layer confinement effect on charge migration in polycarbonate/poly(vinylidene fluorid-co-hexafluoropropylene) multilayered films

“…Microlayer coextrusion has been used to produce a wide range of layered polymeric structures with enhanced mechanical, 1 optical, 2 transport, 3 and dielectric, 4,5 properties. When the layer thickness is reduced to the micro and nanometer scales, profound property changes often occur.…”

“…In the field of dielectrics, submicron thick layers of a poly(vinylidene fluoride-co-hexafluoropropylene) copolymer [P(VDF-HFP)] combined with polycarbonate (PC) exhibit enhanced dielectric properties. 4,5 The enhanced breakdown strength and energy density are often attributed to a barrier effect whereby layers and interfaces impede the propagation of a breakdown channel, which is evidenced by unique treeing patterns around the failure site. 4,5 In the present work, lowfield broadband dielectric spectroscopy (BDS) measurements were carried out and revealed a low frequency relaxation that changed with layer thickness.…”