The influence of mechanical properties in the electrical breakdown in poly-styrene-ethylene-butadiene-styrene thermoplastic elastomer

Abstract

Dielectric elastomer actuators (DEA) are a class of eletro-active polymers with promising properties for a number of applications, however, such actuators are prone to failure. One of the leading failure mechanisms is the electrical breakdown. It is already well-known that the electro-mechanical actuation properties of DEA are strongly influenced by the mechanical properties of the elastomer and compliant electrodes. It was recently suggested that also the electrical breakdown in such soft materials is influenced by the mechanical properties of the elastomer. Here, we present stress-strain measurements obtained on two tri-block thermoplastic elastomers (SEBS 500040 and SEBS 500120, poly-styrene-ethylene-butadiene-styrene), with resulting large differences in mechanical properties, and compare them to measurements on the commonly used VHB 4910. Materials were prepared by either direct heat-pressing of the raw material, or by dissolving in toluene, centrifuging and drop-casting. Experiments showed that materials prepared with identical processing steps showed a difference in stiffness of about 20%, where centrifuged and drop-casted films were seen to be softer than heat-pressed films. Electric breakdown measurements showed that for identically processed materials, the stiffness seemed to be a strong indicator of the electrical breakdown strength. It was therefore found that processing leads to differences in both stiffness and electrical breakdown strength. However, unexpectedly, the softer drop-cast films had a much higher breakdown strength than the heatpressed films. We attribute this effect to impurities still present in the heat-pressed films, since these were not purified by centrifuging.

Theory of Dielectric Elastomers Capable of Giant Deformation of Actuation

“…The measured voltage at failure is taken to be the electrical breakdown voltage. Experiments indicate that the breakdown voltage is a monotonically decreasing function of the prestretch È B ðÞ [23,27]. This trend may be interpreted as follows.…”

“…Also plotted is the condition for electrical breakdown È B ¼ E B H À2 . We have used representative values E B ¼ 2 Â 10 8 V=m, T ¼ 300 K, v ¼ 10 À27 m 3 , " ¼ 4 Â 10 À11 F=m, and H ¼ 1 mm [23,27]. To account for the uncertainty of the available experimental data, we have used a conservative value for FIG.…”

Tuning the mechanical and dielectric properties of clay‐containing thermoplastic elastomer nanocomposites

“…This behavior is most likely related to the reduction of mechanical stiffness upon the alignment of PS nanodomains perpendicular to the electric field direction. In support to this hypothesis, few studies reported that the breakdown strength of SEBS was reduced with decreasing mechanical stiffness . In fact, the electrodes attached to the specimen's surface during the breakdown test exert a compressive force that might result in appreciable deformations at an applied voltage below the intrinsic breakdown voltage, especially in soft elastomeric materials, leading to reduced dielectric strength and failure.…”

Optical transmission gratings tuned by electro active polymers

“…The first material is the commonly used polyacrylic polymer VHB4910 [3], a pressure-sensitive glue (3M). For comparison, the thermoplastic SEBS500120 (SEBS12) [5] has been investigated as well. Unlike the ready to use VHBtape, SEBS films have to be prepared via drop casting.…”