# Review of Soft Actuators Controlled with Electrical Stimuli: IPMC, DEAP, and MRE
## 2 Recent Progress in Development and Applications of Soft Actuators
### Dielectric Electroactive Polymers (DEAPs)
#### 2.2.1 Recent Trends in the Modification of DEAPs  
VHB elastomer is commercial, widely available acrylic tape produced by 3M company. It is a ready-to-use product that only needs to be covered by electrodes to be used as a DEAP. The use of VHB tape makes it possible to obtain DEAP actuators very quickly (no elastomer synthesis is necessary) with reproducible properties of the dielectric layer (Young's modulus, flexibility, thickness, dielectric permeability) and dependent only on the degree of pre-stretching of the tape. This gives the opportunity to study, among others, the effect of the composition of the electrodes on the properties of a DEAP [55; 56; 57]. However, the use of VHB tape has significant limitations. Due to the fact that it is a ready-to-use product, the modification of DEAPs with this elastomer is significantly limited to the modification of the electrode layer. Therefore silicons, next to VHB, are the most important group of elastomers used in the preparation of DEAP actuators. The use of silicone elastomer enables the selection of its composition in a wide range and the easy modification of parameters such as Young's modulus, flexibility, or thickness of the dielectric layer [6; 54]. It also allows the introduction of modifiers into the elastomer that change its mechanical or dielectric properties. This makes it possible to obtain DEAPs with very different properties. The synthesis and modification of DEAPs using silicone elastomers is currently the most popular research direction in the literature. In addition to VHB and silicone elastomers, the information on the use of other polymers for dielectric membranes to obtain DEAP, such as polyurethane elastomers [58] or elastomers based on poly(styrene-b-butyl acrylate-b-styrene) copolymer (SBAS) [30], can be found. However, the use of dielectric membranes other than VHB and silicones is currently very uncommon, which may result from a more complicated procedure for their preparation. Another direction of research on DEAPs is related to the preparation and modification of electrodes. The simplest method of obtaining an electrode on the surface of an elastomer is the use of carbon grease [56; 59]. However, this method does not allow for precise control of its properties, including thickness or mechanical properties. In addition, the use of carbon grease means that after the application of the electrode, it has the consistency of grease all the time (does not dry), which makes it difficult to manipulate the DEAP actuator. Therefore, other materials that can be used as electrodes are often applied, for example, carbon nanotubes [54; 55], carbon powder [60], and others [6; 57]. A significant disadvantage of DEAP actuators is the necessity of high driving voltage application, in the range of several kV, which limits their application in the devices. Therefore, much attention has been paid to reducing the driving voltage of DEAPs. This can be achieved by reducing the thickness of the actuator (both the dielectric layer and electrodes), increasing the dielectric permittivity, and reducing the modulus of the elasticity of the actuator [61; 62]. Reducing the driving voltage below 100 V requires reducing the thickness of the DEAP to a few \(\upmu\)m or even less than 1 \(\upmu\)m, however, such a significant reduction in the DEAP thickness results in a reduction in power density [6]. The solution to this problem may be a construction of a stacked DEAP multi-layer actuator [54; 63], but this requires precise and sophisticated methods of DEAP production. [PERSON] et al. present the fabrication method and results of investigations of multi-layer DEAP actuators [54]. The authors show that proper fabrication of DEAPs allows obtaining  
Figure 4: Principle of operation of the DEAP actuator (source: [52]). actuators composed of 6 to 20 layers with the thickness of each silicone-based dielectric layer about 36 to 10 \(\upmu\)m and the thickness of electrodes equal to 30 nm.