Dielectric Elastomer Materials

While the performance of a dielectric elastomer transducer depends upon the dielectric and elastomeric properties of the polymer material, a great many polymer materials can be used. Because of this flexibility, unlike most other electroactive polymers (EAPs), different polymer materials can be selected for different applications, depending on the desired performance and physical properties. The best performing materials (those with greatest strains) are based on commercially available formulations of silicone rubber (polydimethyl siloxane) and acrylic elastomers such as the VHB series from 3M Corp. (Minnesota, USA) [11]. 

Maximum actuation strain (%) 380 120 Free strain. Strain in generator and sensing modes can be greater than that in actuation. 

Maximum specific energy density in actuation (MJ/m ) 3.4 0.75 Greatest energy density of all field-activated materials can be greater in generator mode. 

Maximum frequency response (Hz) 50000 50 000 Small-strain acoustic measurements frequency response is very dependent on strain and size full response of acrylic is generally much lower (less than 1 kHz), due to viscoelasticity (see Mechanical loss factor below). 

Maximum electric field (MV/m) 440 350 Maximum fields are realizable only in uniform films with few defects. 

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PTBA also exhibits excellent strain fixity (ability to retain its actuated shape upon cooling) and strain recovery. In its softened state PTBA also possesses excellent actuation properties with a breakdown field strength in excess of 250 MV/m, a maximum strain of 335% in area, a maximum actuation stress of 3.2 MPa and an energy density of 1.2 J cm , values that rival even the best of the conventional dielectric elastomer materials. The BSEP is the first active material that possesses bistable actuation with high strain and specific power density. 

Table 1.2 Comparison of dielectric elastomer material properties... 

It follows that many of the most exciting dielectric elastomer materials were discovered via exploratory testing. New formulations of commercially available elastomers are continually being developed and may well be worth exploring. However it is expected that research focusing on developing materials specifically for dielectric elastomer purposes from focused and directed research will provide the best candidates for improved performance in the years to come. 

Thermoplastic block copolymeric elastomers are also of interest as dielectric elastomer materials. These polymers differ from conventional elastomers in that they possess physical crosslinks rather than chemical ones. In these polymers... 

Recently, silicone dielectric elastomer material already coated with compliant electrode material (corrugated silver) was introduced to the market [15]. We also note that the 3 M VHB acrylic (uncoated dielectric elastomer) is also available in large quantities. That such materials can be manufactured in large-scale roll-to-roll operations helps support the notion of the feasibility of large-scale power generation. 

Chapter 6 is focused on dielectric elastomer materials. In particular, a synthetic elastomer is proposed to enhance the actuation performance and energy density. Methods for preparing the materials are discussed, and various material properties as relevant to the actuation performance are characterized and compared with commercially available dielectric materials. In addition, by incorporating suitable additives, the synthetic elastomer has shown favorable behavior for actuation purposes. 

Thirdly, synthetic elastomer was proposed in the effort of finding a new dielectric elastomer material. Comprehensive performance characterization proved that the new material has the highest energy density among the tested materials and the actuation is feasible. Furthermore, by adding different fillers, the properties of the synthetic elastomer material can be adjusted as needed. For instance, different content of DOP and Ti02 show better radial strain of actuation and also increase the elastic energy of the material. 

As EPAM technology has evolved into commercially available products, the performance characteristics have also improved dramatically, with optimizations of the dielectric elastomer materials, manufacturing quality and automated production processes. The applications for the technology will also continue to expand from drop-in replacements... 

Humidity. The electric breakdown strength (and leakage) of dielectric elastomer transducers is often affected by humidity. Lower humidity can dramatically raise the breakdown strength of many dielectric elastomer materials. Humidity can be artificially lowered by using, for example, desiccants. Packaging is an issue for low-humidity operation however, most designs operate at atmospheric conditions. 

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