Dielectric elastomer actuator properties

Benslimane M, Gravesen P (2002) Mechanical properties of dielectric elastomer actuators with smart metallic compliant electrodes. Proc SPIE 4695 150... 

Kofod G, McCarthy DN, Stoyanov H, Kollosche M, Risse S, Ragusch H, Rychkov D, Dansachmuller M, Wache R (2010) Materials science on the nano-scale for improvements in actuation properties of dielectric elastomer actuators. Proc SPIE 7642 764201. doi 10.1117/ 12.847281... 

Benshmane M, Gravesen P, Group MT et al (2002) Mechanical properties of dielectric elastomer actuators with smart metallic compliant electrodes. Proc SPIE 4695 150-157 Benshmane M, Kiil H-E, Tryson MJ (2010a) Electro-mechanical properties of novel large strain PolyPower film and laminate components for DEAP actuator and sensor applications. Proc SPIE 7642 764231... 

Riffle JS, Yilgor I, Tran C et al (1983) Elastomeric polysiloxane modifiers for epoxy network -synthesis of fimctional oligomers and network formation studies. ACS Symp Ser 221 21-54 Risse S, Kussmaul B, BCriiger H et al (2012) Synergistic improvement of actuation properties with compatibilized high permittivity filler. Adv Funct Mater 22 3958-3962 Romasanta LJ, Leret P, Casaban L et al (2012) Towards materials with enhanced electro-meehanical response CaCu3Ti40i2-polydimethylsiloxane composites. J Mater Chem 22 24705-24712 Rosset S, Shea HR (2013) Flexible and stretchable electrodes for dielectric elastomer actuators. Appl Phys A Mater Sci Proeess 110 281-307... 

Today the number of electroactive polymers has grown substantially. There currently exists a wide variety of such materials, ranging from rigid carbon-nanotubes to soft dielectric elastomers. A number of reviews and overviews have been prepared on these and other materials for use as artificial muscles and other applications [1, 2, 7, 10, 11, 13-28]. The next section will provide a survey of the most common electrically activated EAP technologies and provide some pertinent performance values. The remainder of the paper will focus specifically on dielectric elastomers. Several actuation properties for these materials are summarized in Table 1.1 along with other actuation technologies including mammalian muscle. It is important to note that data was recorded for different materials under different conditions so the information provided in the table should only be used as a qualitative comparison tool. 

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. 

A number of approaches have been explored for increasing the dielectric constant of elastomers for DEs. The most common approach involves the addition of high dielectric constant filler materials to an elastomer host. Silicone is of particular interest for this type of approach as it possesses good actuation properties to begin with, is readily available in gel form, and has a low dielectric constant. Results thus far do not appear particularly promising increases in dielectric constant have been met with concomitant increases in dielectric loss and reductions in dielectric breakdown strength [184—186]. It has also been shown that the elastic modulus is affected by the addition of filler [187]. 

Mathew G, Rhee JM, Nah C, Leo DJ, Nah C (2006) Effects of silicone rubber on properties of dielectric acrylate elastomer actuator. Polym Eng Sci 46 1455... 

The dielectric elastomer films presented here appear promising as actuator materials because their overall performance can be good. The available literature indicates that the actuated strains of silicone are greater than for any known highspeed electrically actuated material (that is, a bandwidth above 100 Hz). Silicone elastomers also have other desirable material properties such as good actuation pressures and high theoretical efficiencies (80-90%) because of the elastomers low viscoelastic losses and low electrical leakage [12]. 

TABLE 16.2 Comparison between Two Mechanical Properties of Different Actuating Materials Skeletal Muscles, Thermomechanical (Thermal Liquid Crystals and Thermal Shape Memory Alloys), Electrochemomechanical (Conducting Polymers and Carbon Nanotubes) and Electromechanical (Ionic Polymer Metal Composites, Field Driven Liquid Crystal Elastomers, Dielectric Elastomers)... 

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. 

In any case, polyurethane dielectric elastomers have continued to be studied in the last decade, particularly with regard to the possibility of increasing their actuation performance. It is well known that both dielectric and mechanical properties are key parameters governing the electromechanical response of any dielectric elastomer, which can be in principle improved by an increase of the dielectric constant and by a decrease of the elastic modulus. In order to increase the dielectric permittivity of a polymer elastomeric matrix, various methods are available (Carpi et al. 2008), such as making composites or blends with highly polarizable phases. Table 1 constitutes a non-exhaustive list of works fi-om the literature, mostly relying on such methods for improving the performance of polyurethane dielectric elastomers. The studies are classified in terms of system complexity and component materials. 

Galantini F, Gallone G, Carpi F (2012) Effects of corona treatment on electrical and mechanical properties of a porous dielectric elastomer. IEEE Trans Dielectr Electr Insul 19 1203-1207 Galantini F, Bianchi S, Castelvetro V et al (2013) Functionahzed carbon nanotubes as a filler for dielectric elastomer composites with improved actuation performance. Smart Mater Stract 22 055025... 

In the effort of finding a new DE, the synthetic elastomer is proposed. Its improved performance characterized with dielectric constant, elastic modulus and stress relaxation can be proved with the highest energy density among the materials tested. Under the comprehensive comparisons with the materials commercially available, its possibility as means of actuation is validated. Additionally, the synthetic elastomer properties can be adjusted based on the different contents of the fillers added to the synthetic elastomer. Different additives can be added to this material to create new DE which can be adapted to our requirements. Future research activity may focus on the development of a new composite synthetic elastomer-filler that can accommodate more requirements of our applications. 

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