Nonuniformly Charged Ionic Polymer-Metal Composite Actuators: Electromechanical Modeling and Experimental Validation

— 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. 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