Electroactive polymer actuators ionic actuation mechanism

Oh IK, Jung JH, Jeon JH et al (2010) Electro-chemo-mechanical characteristics of fidlerene-reinforced ionic polymer-metal composite transducers. Smart Mater Stmct 19(7) 075009 Palmre V, Brandell D, Maeorg U et al (2009) Nanoporous carbon-based electrodes for high strain ionomeric bending actuators. Smart Mater Stmct 18(9) 095028 Palmre V, Lust E, Janes A et al (2011) Electroactive polymer actuators with carbon aerogel electrodes. J Mater 21 2577-2583... 

Vunder V, Punning A, Aabloo A (2012) Mechanical interpretation of back-relaxation of ionic electroactive polymer actuators. Smart Mater Struct 21(11) 115023 Zhang M, Atkinson KR, Baughman RH (2004) Multifimctional carbon nanotube yarns by downsizing an ancient technology. Science 306(5700) 1358-1361... 

Non-ionic polymer gel, swollen with dielectric solvent, can be extremely deformed as is the case for non-ionic polymer plasticised with non-ionic plasticiser. Instead of the charge-injected solvent drag as a mechanism of the gel actuation, the principle is based on local asymmetrical charge distribution at the surface of the gel18. The mechanism can also be applied to non-ionic elastomers in which the motion of the polymer chain is relatively free. In spite of their many difficulties for practical actuators, polyelectrolyte gels and related materials are the most interesting electroactive polymer materials. 

There is growing interest in biomimetic motions, which imitate the action of natural muscles. Since such motions are difficult to realize using conventional appliances such as mechanical, hydraulic, or pneumatic actuators, research efforts are focused on the development of new muscle-like actuators. Electroactive polymers (EAPs) including polymer gels [63], ionic polymer-metal composites (IMPCs) [64], conductive polymers [56], and carbon nanotubes [65] are candidates to address the performance demands. 

The overall electroactivity of carbon-based actuators, including CNTs, CDCs, or activated carbons, predicates on two main actuation mechanisms. The first principle is based on the electronic (metallic) conductivity of carbon material. Actuators of such type need high electrical potential (field) for actuation. Actuation occurs due to carbon-carbon interaction change due to high electrical field and increased temperature (electrothermal effect) (Liu et al. 2014 Zhang et al. 2014). Another principle is diffusion of ions and ion pairs induced by applied low potential as shown in Fig. 1. These transducers usually combine carbon materials with polymer matrix and some ionic conducting media. They seem to have much more possible applications in the near future (Asaka et al. 2013). 

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