279 Review Received: 15 June 2009 Revised: 29 July 2009 Accepted: 3 September 2009 Published online in Wiley Interscience: 12 January 2010 (www.interscience.wiley.com) DOI 10.1002/pi.2759 Ionic polymer – metal composite mechanoelectrical transduction: review and perspectives Deivid Pugal, a,b Kwangmok Jung, a Alvo Aabloo b and Kwang J Kim a* Abstract This paper presents a comprehensive review of the use of ionic polymer-metal composite (IPMC) materials as mechanoelectrical transducers. Recently increasing emphasis has been put on the research of IPMCs as displacement or velocity sensors for various applications. This has resulted in various theories and models to describe the mechanoelectrical transduction phenomenon. The paper gives an overview of the proposed transduction principles, developed models and the latest applications. In more detail, the history of IPMC materials, the physics and the electrochemistry behind the mechanoelectrical transduction, different black-box and gray-box models, and novel real-world mechatronics-related applications are discussed throughout the paper. However, despite the latest advancements in the research of IPMC transduction, there is still a certain amount of controversy regarding some of the IPMC sensorial properties. For instance, it has been noticed by several authors that there is a signal delay when bending an IPMC. The general understanding of the physical principles about regular IPMC mechanoelectrical transduction is rather good. In the last section of the paper novel results are presented for copper-coated IPMC materials. Apparently the electrochemistry behind the transduction for copper-coated IPMCs is significantly different. Besides ionic diffusion, chemical reactions on the electrodes also occur and dominate the actuation process. Experimental results show some promising opportunities for designing new copper-coated IPMC-based sensors. c  2010 Society of Chemical Industry Keywords: IPMC; mechanoelectric transducer; sensor; electroactive polymer INTRODUCTION Ionic polymer – metal composite (IPMC) materials have been exten- sively studied during the last two decades. Low-voltage bending of a Nafion-based polyelectrolyte membrane–platinum compos- ites was reported in 1992 by Oguro et al. 1 From there on, many studies have considered IPMC mechanoelectrical properties. 2–7 IPMC materials consist of a thin ionomeric membrane with typical thickness of upwards of 100 μm. 8 Typical membrane materials are Nafion  , Teflon  and Flemion  . 9 The membrane is coated with a thin layer of a noble metal electrode, such as platinum. Sometimes an additional layer of gold is added on the surface to improve the electric conductivity of the electrodes. As there are anions fixed to the polymer backbone, the membrane also consists of freely movable cations, so the overall charge of the material is balanced. Typical cations are Na + , Ka + , Li + and Cs + in water solution. Dry forms of IPMCs have also been studied, where an ionic liquid such as tetra-n-butylammonium (TBA + ) is used. 9,10 The general conceptual design of IPMCs was first described by Shahinpoor and co-workers in 1992. 11,12 A swimming robotic structure based on IPMC actuators was proposed. The kinematic equations discussed were based on the work of Segalman et al. who presented a number of papers about the modeling of IPMC materials. 11,13,14 The diffusion equation describing the evolution of solvent concentration and therefore the strain of a polymeric gel material was proposed in 1992. 12 In 1993 and 1994 Segalman et al. also published a finite element analysis of polymeric gel materials. 14,15 In following years attempts to formulate the mechanoelectrical theory for IPMC materials were made. Shahinpoor and co-workers 16–18 presented a non-homogeneous large deformation theory of ionic polymer gels in electric and pH fields. The proposed model considered the spatial distribution of cations and anions inside the material due to the applied electric field. The deformation of IPMCs was defined as a function of electric field strength, dimensions and material physical parameters. 16–18 In 2000 De Gennes et al. presented the first phenomenological theory of sensing and actuation of IPMCs. 19 Li and Nemat-Nasser presented a model of the mechanoelectrical response of IPMCs: it considered the electrostatic forces inside the material and the cluster morphology of Nafion. 20 In 2002 Nemat-Nasser stressed the role of hydrated cation transport within clusters and polymeric networks of IPMCs. 21 Weiland and Leo published a model where the rotation of individual dipoles within a cluster was studied and related to the actuation of IPMCs. 22 In 2003 Nemat-Nasser and Wu presented an extensive study of the actuation properties of IPMCs with various membrane materials and types of cations. 9 To summarize the study, a typical Nafion-based IPMC in most cation forms, when subjected to a small potential, undergoes a fast bending towards the anode, followed by a slow relaxation towards ∗ Correspondence to: Kwang J Kim, Mechanical Engineering Department, Uni- versity of Nevada, Reno, NV 89557, USA. E-mail: kwangkim@unr.edu a Mechanical Engineering Department, University of Nevada, Reno, NV 89557, USA b IMS Lab, Tartu University, Estonia Polym Int 2010; 59: 279–289 www.soci.org c  2010 Society of Chemical Industry