electromechanical instability

A highly deformable capacitor made of a soft dielectric and two conformal

electrodes can switch between two states discontinuously, by a first-order transition, as the total

charge varies gradually. When the total charge is small, it spreads evenly over the area of the

capacitor, and the capacitor deforms homogeneously. When the total charge is large, it localizes in

a small region of the capacitor, and this region thins down preferentially. The capacitor will

<http://www.sciencedirect.com/science/article/pii/S0045782513000790>

Recently accepted for publication in Soft Matter:

(http://pubs.rsc.org/en/Content/ArticleLanding/2013/SM/C2SM27375F)

(http://dx.doi.org/10.1039/c2sm27375f)

Snap-through actuation of thick-wall electroactive balloons

Stephan Rudykh (a), (c), Kaushik Bhattacharya  (c) and Gal deBotton (a), (b)

(a) Department of Mechanical Engineering, Ben-Gurion University, 84105 Beer-Sheva, Israel

Electro-creasing instability in deformed polymers: experiment and theory

Qiming Wang, Mukarram Tahir, Lin Zhang, and Xuanhe Zhao*

Soft Matter, In Press 

Creasing to cratering instability in polymers under ultrahigh electric fields

Qiming Wang, Lin Zhang, and Xuanhe Zhao*

Physical Review Letters, In press

NONEQUILIBRIUM THERMODYNAMICS OF DIELECTRIC ELASTOMERS
Xuanhe Zhao, Soo Jin Adrian Koh, Zhigang Suo

Theory of dielectric elastomers capable of giant deformation of actuation
Xuanhe Zhao, Zhigang Suo
Physical Review Letters, 104, 178302 (2010)

Electromechanical instability in semicrystalline polymers
Xuanhe Zhao , Zhigang Suo
Abstract

      This paper studies a gel formed by a network of cross-linked polymers and a species of mobile molecules. The gel is taken to be a dielectric, in which both the polymers and the mobile molecules are nonionic. We formulate a theory of the gel in contact with a solvent made of the mobile molecules, and subject to electromechanical loads. A free-energy function is constructed for an ideal dielectric gel, including contributions from stretching the network, mixing the polymers and the small molecules, and polarizing the gel.

      This letter describes a method to analyze electromechanical stability of dielectric elastomer actuators.  We write the free energy of an actuator using stretches and nominal electric displacement as generalized coordinates, and pre-stresses and voltage as control parameters.  When the Hessian of the free-energy function ceases to be positive-definite, the actuator thins down drastically, often resulting in electrical breakdown.  Our calculation shows that stability of the actuator is markedly enhanced by pre-stresses.

Active polymers are being developed to mimic a salient feature of life: movement in response to stimuli. Large deformation can lead to intriguing phenomena; for example, recent experiments have shown that a voltage can deform a layer of a dielectric elastomer into two coexistent states, one being flat and the other wrinkled. This observation, as well as the needs to analyze large deformation under diverse stimuli, has led us to reexamine the theory of electromechanics.