1 Abstract— An IPMC composite is an electroactive material that behaves in an electric field similarly to biological muscles. This intelligent material is leading to a new emerging technology called non-uniformly charged IPMC actuators. This paper introduces first an IPMC analytical modeling approach for its electromechanical characterization. The model considers, for the first time, the action of gravitation force in its electric and mechanic characteristics, which is important for large IPMC actuators. To demonstrate the efficacy of the model, two non-uniformly charged IPMC actuators were fabricated and tested. Experimental results are presented to validate the model and verify its effectiveness in the design of non- uniformly charged IPMC actuators. Index Terms—Electric actuators, Ionic polymer-metal composites, IPMC, Intelligent materials, Polymers I. INTRODUCTION Conventional actuators using electromagnetic forces [1] are still important in motion control. However, they have difficulty in satisfying the new and advanced demands from high performance machines [2], [3]. Therefore, seeking for innovative actuators [4] as shape memory alloy [5], magnetostrictive [6], and more recently IPMC actuators [7], [8], is today an intense research activity. IPMCs are functional materials [9] being electroactive polymers [10]–[11]. They are made by Nafion polymer electroplated with gold or platinum with negative sulfonates (SO 3 - ) fixed to its structure. The IPMC operates as actuator or sensor [12]. As sensor, it has to be subjected to an external mechanical pressure resulting in an electric current or voltage at its terminals. The IPMC has the disadvantage of needing an electrolyte for its operation, usually sodium electrolyte or ionic liquids [13]. The IPMC needs continuing hydration to avoid dryness problems which increase its stiffness and decrease its actuating/sensing capabilities. Two procedures were proposed to avoid IPMC dehydration: its encapsulation [14]–[15], or using an electrolyte with low evaporation constant [16]–[17]. When in Copyright © 2009 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to pubs-permissions@ieee.org sodium electrolyte, for example, the IPMC has water as solvent with Na + being the mobile ions. The IPMC conducts Na + across its membrane, showing its property of being permeable to them but not to Cl - . Metal electrodes plated in the Nafion must be flexible and porous because the IPMC must be bendable, and porous because they must allow the passage of positive ions from the electrolyte to the polymer. IPMC actuators can be commanded by voltage or current [18], [19]. Fig. 1(a) shows that when a voltage is applied to an IPMC, Na + ions are dislocated from positive to negative potential. This causes the appearing of an internal electric field acting on fixed negative ions and causing electrostatic forces transmitted to Nafion structure, causing an IPMC deformation. Fig. 3(a) shows that during the electric process caused by an applied voltage, some positive ions come out of the IPMC through the negative electrode due to diffusion flow since electrodes are porous. Hence, since the internal negative ions’ charge is not compensated with new positive ones, the IPMC suffers a so-called relaxation of its membrane and the IPMC returns to its steady position. If an electric current is applied instead a voltage, as in Fig. 1(b), the relaxation problem does not occur because the flux of positive charges is compensated continually. Applying an electric current, the positive ions will be in constant migration from outside to inside or inside to outside of the IPMC, keeping the flow of positive charges (charges that are balanced out with the entering positive charges), maintaining constant the electric force density in the IPMC. The authors previously published works [17] and [19] show a series of experimental results that illustrate the non- relaxation phenomenon when the IPMC is under current control. + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + (a) Non-Uniformly Charged Ionic Polymer-Metal Composite (IPMC) Actuators: Electromechanical Modeling and Experimental Validation P.J. Costa Branco, B. Lopes, and J.A. Dente