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Electromechanical Response of Multilayered Polymer Films for High Energy Density Capacitors

Published online by Cambridge University Press:  17 June 2011

Mason A. Wolak ,
James S. Shirk ,
Matt Mackey ,
Joel Carr ,
Ann Hiltner  and
Eric Baer
Mason A. Wolak
Affiliation:
Optical Sciences Division, U.S. Naval Research Laboratory, Washington, DC 20375. USA.
James S. Shirk
Affiliation:
Optical Sciences Division, U.S. Naval Research Laboratory, Washington, DC 20375. USA.
Matt Mackey
Affiliation:
Department of Macromolecular Science and Center for Applied Polymer Research, Case Western Reserve University, Cleveland, OH 44106-7202. USA.
Joel Carr
Affiliation:
Department of Macromolecular Science and Center for Applied Polymer Research, Case Western Reserve University, Cleveland, OH 44106-7202. USA.
Ann Hiltner
Affiliation:
Department of Macromolecular Science and Center for Applied Polymer Research, Case Western Reserve University, Cleveland, OH 44106-7202. USA.
Eric Baer
Affiliation:
Department of Macromolecular Science and Center for Applied Polymer Research, Case Western Reserve University, Cleveland, OH 44106-7202. USA.
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Abstract

Multilayered films comprising alternating layers of polycarbonate (PC) and poly(vinylidene fluoride-hexafluoropropylene) (P[VDF-HFP]) show an enhanced dielectric strength (E B> 750 kV/mm) and an increased energy storage density (U d ~ 13.5 J/cm3) compared to monolithic PC and P[VDF-HFP] films. Here the role of electromechanical effects in the breakdown of multilayer films is explored both by imaging the changes in the layer structure caused by electrical fields below the breakdown field and by a direct measurement of the strain in multilayer PC/ P[VDF-HFP] films subjected to similar fields. Focused Ion Beam (FIB)/ Scanning Electron Microscopy (SEM) images of the layer structure in films subjected to repeated cycles at near-breakdown fields showed local changes in the thickness of individual layers, suggesting that mechanical forces arising from field-induced compression may play a role in the steps preceding the breakdown. The directly measured field induced strain showed evidence for both an elastic and a flow component to the strain. The mechanical responses of films with ≤ 50 vol% P[VDF-HFP] were modeled as simply the sum of an elastic and viscous flow. The observed electromechanical properties vary with the layer structure. This suggests that multilayering polymers may provide a means to mitigate deleterious electromechanical effects in low modulus, high dielectric materials.

Keywords

stress/strain relationshipdielectricscanning electron microscopy (SEM)
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1312: Symposium HH/II/JJ – Polymer-Based Materials and Composites—Synthesis, Assembly and Applications , 2011 , mrsf10-1312-hh02-04
Copyright
Copyright © Materials Research Society 2011

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References

REFERENCES

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