Performance of the IPMC Actuator

During the past decade, much work has been done on the development of the IPMC actuator. In this section, typical examples of our previous experimental results with the Nafion/Au and Hemion/Au actuators are summarized. 

The ionic forms of the Nafion and Flemion affect the response speed and the bending amplitude of the electromechanical response of the IPMC actuator as shown in 

In order to explain the actuation behaviour and develop its performance, many workers have modelled the IPMC actuator. Some have developed a black box model, in which the IPMC actuator is considered as a black box, and the response function for determining the relationship between input and output [21-24]. The black box model is useful for applications. However, we cannot understand the mechanism of the electromechanical response of the IPMC. 

In this section, a physics-based IPMC model based on the electro-responsive gel theory is introduced. We proposed an IPMC model, in which the bending response is attributed to the electro-osmotic flow in the ion gel film, in 2000 [19], taking into account only the water flow in the membrane. In the same year, de Gennes et al. [25] gave a more comprehensive theory using the phenomenological equation for the electric current (jg) and the water flux (js) based on the irreversible thermodynamics  

The general model was applied to the ion cluster structure of fluorinated ion exchange membrane shown in Eigure 5.9. The friction constant of free ions is given by the Stokes-Einstein law  

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The plating electrodes for optimum performance of the IPMC actuator should have the... 

Figure 5.6 Schematic representations of the measuring setup for the performance of the IPMC actuator, (a) Displacement measurement, (b) Force measurement.

Since an IPMC functions as a pathway for hydrated cations, its properties will be expected to affect the performance of an IPMC actuator. The membrane materials used in IPMCs have so far been limited to a few commercially available perfluorinated ionic polymers, such as Nafion, and the thickness of the IPMC has also been restricted to the available thickness of the commercial membrane [67]. However, IPMC actuators employing new ionic membranes have now been reported [68]. The membranes are prepared from fluoropolymers grafted with polystyrene sulfonic acid (PSSA). IPMCs assembled with these membranes have been shown to exhibit at least several times larger displacements than the Nafion-based IPMC with similar thickness. 

The experimental setup for measuring eleetromechanical performance of an IPMC actuator consists of a clamp to mount the IPMC sample, a data recording device (e.g., digital oscilloscope or computer equipped for data acquisition), a function generator, a current amplifier, a force sensor, and a laser displacement sensor or a video camera (Figs. 4 and 5). The process diagram of electromechanical characterization is given in Fig. 6. 

In the previous sections we have seen that the electrodes of an IPMC are not bulk metal. Rather, the electrode structure depends largely on the electroless plating procedure and the deposition conditions. As was also seen, the electrode characteristics affect the performance of the actuation considerably. Here an electrode model accommodating various characteristics is proposed. The model assumes that the electrode is composed of particles and voids between the particles. The model can be used to imder-stand the influence of the parameters, such as electrode thickness, particle size, particle gap, etc., on the electrical properties of IPMCs [Kim et al. (2007b)]. 

Described in this chapter, are the basic aspects of IPMC actuator fabrications, measurement methods for testing, acmator performances, physics-based models and recent development of the material of the IPMC-like ionic polymer based acmators, based on our previous works. Interested readers can refer more comprehensive review articles on the IPMCs [6-9]. 

It is also essential to observe the morphologies of the plated electrodes using SEM, TEM, or AFM. Figure 4 shows a SEM image of a cross section of a Pt-plated Nation 117 membrane. As can be seen from the figure, the morphology of the plated electrodes determines the electrochemical and mechanical properties of the IPMC and thus its electromechanical actuation performance. 

Fig. 7 Results of cyclic voltammetry (CV) and displacement measurements (deflection) performed on the Pt electrode of an IPMC actuator in an H2SO4 solution (Reproduced from Kim et al. 2011)...

Due to the wide range of IPMC actuators produced all over the world, there is a pressing need for an objective method to compare their electromechanical performance. The most common way of comparing bending actuators is based on estimating the difference of strains in the electrodes of the IPMC. As a result of the... 

Chapter 2 is focused on physical principles of IPMCs. It starts with an introduction to the fundamentals of IPMCs, including the fabrication techniques, and then takes a careful look at the effect of electrodes on material behavior and actuation performance. Several novel approaches, including a fluorescence spectroscopic visualization method, are then used to yield unique insight into IPMC actuation behaviors, such as the back-relaxation phenomenon. More sophisticated configurations than a singlelayer bender are also discussed in this chapter. 

The forth direction, analytical modeling for understanding the behaviors of these materials, has been popular approach. Testing and characterization have been conducted for developing the models. Such attempts have been done especially for ionic polymer metal composites (IPMCs)[58, 70, 72, 120]. Nemab Nasser and his co-workers carried out extensive experimental studies on both Nafion- and Flemion-based IPMCs consisting of a thin perfluorinated ionomer in various cation forms, seeking to imderstand the fundamental properties of these composites, to explore the mechanism of their actuation, and finally, to optimize their performance for various potential applications[121]. They also performed a systematic experimental evaluation of the mechanical response of both metal-plated and bare Nafion and Flemion in various cation forms and various water saturation levels. They attempted to identify potential micromechanisms responsible for the observed electromechanical behavior of these materials, model them, and compare the model results with experimental data[122]. A computational micromechanics model has been developed to model the initial fast electromechanical response in these ionomeric materials[123]. A number... 

IPMCs are smart materials that exhibit electromechanical (actuator) and mechanoelectrical (sensor) applications. Table 9.1 shows performance properties of state-of-the art IPMCs [5]. They bend quickly under a low voltage, as first reported by Oguro and his co-workers [6]. Later, Abe et al. introduced the important role of existent counter ions and their influence during the bending [7]. Asaka and Oguro introduced a theory of the actuation mechanisms [8] Shahinpoor and Kim demonstrated that the ionic polymer actuator performance depends on the type of cation [9] and further developed a two-step fabrication method [10] in accordance with their findings. In addition, other groups tried to incorporate various metals as electrode materials to articulate physical properties or electrical responses [11-14]. 

IPMC actuators exhibit a typical strain of 0.5 %, strain rate of 3 %/s and a typical stress of 3 MPa. They are actuated at potentials of <10 V [42]. The performance of these actuators has been improved by using various combinations of cations [23-25] and different types of electrodes, such as platinum-copper [26]. In this chapter a brief overview of different designs and test procedures using this type of actuators is presented, as similar approaches could also be employed in conjugated polymer driven devices. IPMC based steerable catheters are further described in another chapter of this book. 

He Q, Yu M, Song L et al (2011) Experimental study and model analysis of the performance of IPMC membranes with various thickness. J Bionic Eng 8 77-85 Jo CH, Pugal D, Oh IK et al (2013) Recent advances in ionic polymer-metal composite actuators... 

Lee JW, Yoo YT (2009) Anion effects in imidazolium ionic liquids on the performance of IPMCs. Sens Actuators B 137 539-546... 

Rajagopalan M, Jeon JH, Oh IK (2010) Electric-stimuli-responsive bending actuator based on sulfonated polyetherimide. Sens Actuators B 151 198-204 Shahinpoor M (1992) Conceptual design, kinematics and dynamics of swimming robotic stmctures using ionic polymeric gel muscles. Smart Mater Stmct 1 91-94 Shahinpoor M, Kim KJ (2000) The effect of surface-electrode resistance on the performance of ionic polymer-metal composite (IPMC) artificial muscles. Smart Mater Stmct 9 543 551 Shahinpoor M, Kim KJ (2001) Ionic polymer-metal composites - I. Fundamentals. Smart Mater Struct 10 819-833... 

This chapter provides an overview of the materials used for manufacturing IPMC actuators and sensors. Recently, considerable effort has been put into investigating various electrode materials and ionic polymer membranes to increase the aetuation performance of IPMC and overcome some of the shortcomings to improve their reliability and stability. Various metallic and nonmetallic electrode materials with notable eleetroehemical and electromechanical properties have... 

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