Dielectric elastomer materials for large-strain actuation and energy harvesting: a comparison between styrenic rubber, natural rubber and acrylic elastomer

Abstract

This paper compares the performance of commercially available membranes made of styrenic rubber, natural rubber and acrylic elastomer for dielectric elastomer transducers operating in the large strain regime. Following a detailed description of the adopted experimental set-up and procedures, the results of a comprehensive electro-mechanical characterization of the three materials are reported to highlight the following dependencies: dielectric strength versus stretch, electrical conductivity versus electric field, dielectric constant versus stretch, stress versus stretch and strain rate. This includes the fitting of the experimental data with constitutive equations which provide material property values that can be used for model-based analysis, design and control of dielectric elastomer actuators and generators operating at large levels of strain amplitudes (like, for instance, transducer featuring actuation and generator strains over 100%) or in the presence of large pre-strains (over 100 %). Performance metrics relying on the identified constitutive parameters are introduced in order to discuss the specific pros and cons of the considered elastomers for the development of practical dielectric elastomer transducers.

A Review of Dielectric Elastomer Generator Systems

“…[18,31] Dielectric properties similar to those of natural rubber have been recently observed also in styrene-based synthetic rubber, whose application in DEGs is to date barely explored. [61] Silicones are regarded as strategic for future DE applications as they can be processed following different manufacturing techniques [68,69] and offer room for electromechanical properties improvement via physicochemical modification of their components. [60] Table 2 shows an overview of the material properties of three commercial elastomers, taken as representatives of the above mentioned DE categories (acrylic, rubber, and silicone).…”

“…Elastosil silicone has been originally commercialized as a general-purpose raw material, tough recently high-tolerance thin films have been also produced purposely for DE application. [70] The properties of VHB, and Oppo Band in Table 2 were obtained by Chen et al [61] Unless otherwise referenced, the properties of Elastosil silicone refer to Elastosil 2030 films and they have been measured here using setups and procedures similar to those described in the study by Chen et al [61] The shear modulus and the mechanical loss refer to pure-shear tensile tests with maximum strain equal to roughly 90% the elongation at break and strain rate between 0.08 and 0.8 s À1 ; the BD electric field ranges account for different applied stretches or voltage waveforms during the tests; the conductivity is measured at different applied electric fields between 10 and 80 kV mm À1 .…”

“…DEG mechanical losses mainly consist in rate-dependent viscous losses [56] that increase proportionally with the strain rate, although some DE materials also exhibit a pseudoelastic behavior characterized by rate-independent hysteresis. [61,62] If the dissipated-to-stored mechanical energy ratio for a DE material is high, mechanical losses cause a significant drop in the DEG efficiency, though they do not inhibit a DEG's ability to produce a positive electrical power output and do not affect the maximum convertible electrical energy density. DEG electrical losses are due to the R-C dynamics within the DEG, and they lead to reductions in both the DEG efficiency and the convertible energy density.…”

“…Time constant τ d is a material property of the DE, and it quantifies the DEG selfdischarging characteristic time due to the material conductivity, regardless of the DEG topology. [61] Due to non-negligible electrode resistivity, the electric field on some portions of the DE material (far from the connections with the power electronics) might result in being lower than the target static value, limiting the DE material capability to uniformly achieve large convertible energy densities. [63] Indicating with R s the sheet resistance of the compliant electrodes, the characteristic R-C time constant of the electrodes-DE assembly is τ e ¼ R s C DEG .…”

Dielectric Elastomer Actuator for Soft Robotics Applications and Challenges

“…DEA using 3M VHB acrylic elastomer with large pre-strain shows the strain over 380% [3]. Recently, various silicone elastomers, such as Dow Corning Sylgard 186, Dow Corning HS3, Nusil CF19-2186, Wacker Elastosil RT 625, Wacker Elastosil P7670, THERABAND YELLOW 11726, and OPPO BAND GREEN 8003 were tested as DE materials [11,12]. Compared to the acrylic elastomers, silicone elastomers have relatively low DE constants, and thereby require higher electrical fields to achieve high strain.…”