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Effect of mechanical pre-stretch on the stabilization of dielectric elastomer actuation

Bo Li's picture

A dielectric elastomer is capable of giant electromechanical actuation but fails at breakdown due to instability under certain conditions with a small deformation. By applying a mechanical pre-stretch, one obtains a stabilized large actuation.

In this paper, we measured the dielectric constant and critical voltage of a polyacrylic dielectric elastomer subject to both equal and unequal biaxial stretch, and modelled its actuation by employing the Gent strain energy function with a microscopic view to characterize the nonlinear stiffening behaviour and the electrostrictive effect in the deformation.

With this model we are able to estimate the maximum actual stretch at levels of prestretch and the dielectric strength as a function of deformation.

The mechanical pre-stretch contributes in several ways to the stabilization of dielectric elastomer, by eliminating the pull-in instability, by
generating electrostriction, by improving the breakdown strength, as well as by reducing the membrane thickness which consequently lowers the
voltages required for activation.


This paper is published by  J. Phys. D: Appl. Phys. 44 155301 doi: 10.1088/0022-3727/44/15/155301


Adrian S. J. Koh's picture

Dear Bo,

You have some nice experimental data, characterizing the dielectric constant and dielectric strength for a DE, under various levels of pre-stretch.  I like this, as such data are grossly absent from the existing literature!

In fact, the actuation capacity of DE is limited by a simple fact: Electromechanical Instability (or Pull-In Instability).  Assuming that we do not have giant dielectric strength (that is, > 500 MV/m, which is mostly true as existence of imperfections causes premature breakdown), to improve the capacity to actuate, EMI must be suppressed or removed.  To do this, we either suppress the peak, or move the limiting stretch closer to the peak, or both.  Elastomer with interpenetrating networks achieves the latter, while pre-stretching achieves both.  In your study, you have identified an interesting third mechanism - Electrostriction, which does the latter.  In fact, I can identify a fourth mechanism - Polarization Saturation, that does the former (suppressing the peak).  It will be interesting to know if polarization saturates in a DE in your experiments.

With that, I think it may interest you to read a paper my colleagues and I recently published in J. Polym. Sci. B, 49, 504:

Please feel free to provide us with comments.




Bo Li's picture


 Thank you Andrian for your comment and your excellent paper in J. Polym. Sci. B


   In this work, we don't invoke the polarization saturation for it is hardly achievable under the applied electric field. However in other dielectrics, i.e. dielectric gel or porous dielectric with polar liquid, the saturation might be attainable.


   We are currently working on the mechanism of how the polarization saturation stabilizes the actuation, and hope it will bring more interesting conclusions.


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