Sub-percolative composites for dielectric elastomer actuators

Abstract

Dielectric elastomer actuators (DEA) based on Maxwell-stress induced deformation are considered for many potential applications where high actuation strain and energy are required. However, the high electric field and voltage required to drive them limits some of the applications. The high driving field could be lowered by developing composite materials with high-electromechanical response. In this study, a sub-percolative approach for increasing the electromechanical response has been investigated. Composites with conductive carbon black (CB) particles introduced into a soft rubber matrix poly-(styrene-co-ethylene-co-butylene-co-styrene) (SEBS) were prepared by a drop-casting method. The resulting composites were characterized by dielectric spectroscopy, tensile tests, and for electric breakdown strength. The results showed a substantial increase of the relative permittivity at low volume percentages, thereby preserving the mechanical properties of the base soft polymer material. Young's modulus was found to increase with content of CB, however, due to the low volume percentages used, the composites still retain relatively low stiffness, as it is required to achieve high actuation strain. A serious drawback of the approach is the large decrease of the composite electric breakdown strength, due to the local enhancement in the electric field, such that breakdown events will occur at a lower macroscopic electric field.

Morphology-controllable graphene–TiO2 nanorod hybrid nanostructures for polymer composites with high dielectric performance

“…For example, the breakdown voltage of the poly-(styrene-coethylene-co-butylene-co-styrene) composite with 4 vol% carbon black particles is only 1.6 V mm À1 , 27 times lower than that of the matrix. 45 The reduction in breakdown strength arises from a tunneling charge injection at high electric fields. 21 Introducing an additional interface layer between the conductive fillers provides a promising approach to suppress the tunneling current of the composites at high fields, which may increase the breakdown strength of the composite when compared to a conductive filler-polymer composite.…”

Flexible enhanced energy density composites for dielectric elastomer actuators

“…Employing high permittivity insulating particles requires high filler concentrations to have an impact on the relative permittivity, which inevitably lead to undesirable mechanical reinforcement, thereby counteracting the permittivity benefit [12][13][14]. Sub-percolative approach based on dispersing conductive particle in the elastomer matrix lead to an increase in permittivity of several orders of magnitude, which has the advantage of minimal influence on the mechanical properties due to small amounts of filler required [16]. However, a serious drawback of the approach is the lowering of the electric breakdown strength of the composite, which offsets the high permittivity gains with respect to stored electrical energy [15].…”

“…Another approach allowing reduction in the operating voltage, would be decreasing the thickness of the elastomer film. However due to the difficulties related with producing and handling of very thin elastomer films, the research interest has been focused mainly on developing elastomer materials with high permittivity [10][11][12][13][14][15][16][17].…”