Ionic EAPs

So why do some ionic EAPs contract The movement of the ions of the electrolyte comes into play, but to exploit contraction, the placement of the electrodes is also very important. If contraction, rather than bending is desired, the negative electrode is placed external to the EAP, while the positive electrode remains internal (embedded) in the EAP (Fig. 4.5). In the case of the contractile EAP composed of PMA, the ions along the main polymer chains are weak acetic acid groups. The electrolytic solution typically used to swell the gel and provide for good electroactivity is a dilute sodium chloride solution, such as isotonic saline solution. When the electric input is applied to the PMA EAP based actuator with this electrode configuration, the EAP of the actuator contracts quickly and substantially. In selected EAP formulations, when the polarity is reversed, expansion occurs, and contraction and expansion can be cycled repeatedly in selected PMA based EAP materials and actuators [3, 5]. 

Overview Ionic EAPs Capable of Contraction and Expansion-Contraction Cycles... 

Practical Considerations when Designing Actuators Using Ionic EAPs... 

The polymer-metal interface between the ionic EAP and the embedded elec-trode(s) was significantly improved using plasma treatment. Based on the water drop surface contact angle tests and mechanical testing, oxygen plasma-treated stainless steel and titanium led to much better adhesion between the electrodes and the EAPs. For both stainless steel and titanium, XPS confirmed the presence of a... 

An ionic EAP based actuator (3.16 g), with an embedded spiral stainless steel wire as the positive electrode and an external platinum negative electrode, was mechanically tested isometrically with a 587.7 mg counterweight. The experimental design used a Mettlar analytical balance and a pulley system (Fig. 4.24). The isometric mechanical testing of an activation-relaxation cycle is shown in Fig. 4.25. This was a fairly large actuator. We have observed that the smaller the actuator, the faster and more pronounced the contraction. 

Molecular modeling and experimentation were performed to determine how and why these EAPs contract. Without electric input, the positively charged cations remain very tightly bound to the ionic EAPs. Once electricity is applied to these EAP based materials and actuators, cations and water move very rapidly from a three-fold effect due to ion migration, localized pH effects at the electrodes, and osmosis, producing a rapid pronounced contraction of the EAP. These recent developments, and fundamentally, the thorough understanding of the contraction phenomenon, are important in the field of electroactivity because of the ability of contraction and contraction-expansion to produce biomimetic life-like motion. 

The purpose of this book is to provide a focused, in-depth, yet self-contained treatment of recent advances made in several most promising EAP materials. In particular, the book covers two classes of ionic EAPs, ionic polymer-metal composites (IPMCs) and conjugated polymers, and one class of electronic EAP materials, dielectric elastomers. Ionic EAPs realize actuation through ion transport, and thus require very low voltages (a few volts) to operate, but their bandwidths are typically lower than tens of Hz. On the other hand, dielectric elastomers rely on electrostatic forces to operate and thus require high actuation voltages (kilovolts), but... 

These polymers are studied as candidate materials for pseudo-muscular actuators. Such devices are conceived to promote a functional biomimesis of natural muscles [182,183]. The following sections provide a brief description of the basic features of the less diffused EAP materials and devices ionic EAP and dielectric elastomers. 

The usability of such actuators for practical applications still requires the solution of several problems in the case of ionic EAP, while possible uses are expected in the near future for dielectric elastomer devices. 

In miniaturized technical applications, especially when the volume of the electrolyte is limited and encapsulated, the formation of gas by hydrolysis is a critical issue. Hydrolysis occurs at potentials in an electrochemical cell higher than 1.24 V. Therefore, an appropriate selection of the material for the counter electrode (CE) needs to be addressed when designing a miniaturized ionic EAP system. Voltammograms of a PPy/Au bilayer (area 10 mm 2 mm thickness 30 pm) in 0.1 M NaDBS are given in Figure 15.9. Each plot refers to a different electrode material applied as CE gold on chromium on silicon. 

Within each group there are a wide variety of specific actuation mechanisms and related types of materials. In particular, ionic EAPs include polymer gels [3], ionic polymer-metal... 

Ionic EAP Polymer gels Poly(acrylic acid) (PAAc) Poly(vinyl alcohol) (PVA) Modified poly(acrylonitrile) (PAN) [31... 

A brief review is given on modeling approaches for ionic EAPs. Specifically, numerical models considering chemical, electrical, and mechanical stimuli are subject of matter. The literature review is given in a chronological order. 

This chapter has been dedicated to all people wanting to make their first step in the field of ionic EAP researcher, teaeher or even students. This chapter tried to gather usefiil and precise experimental details on how to fabricate and to characterize actuators based on such astonishing materials. 

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