Ionomeric Polymer-Metal Composites (IPMCs) are sandwich-like materials based in a polymeric membrane covered on both sides by metallic electrodes. Its operation mechanism consists of hydrated ions migration in response to an external electrical field generated between the electrodes, leading to a spatially nonuniform mass accumulation which causes the device to bend. Its performance as an actuator depends mainly on the environment's relative humidity and electrical stimuli. Consequently, IPMCs present variations in the electromechanical properties exhibiting nonlinearities and time-varying behaviors, limiting the major applications. For this reason, this paper investigated a PI controller performance to overcome these drawbacks and effectively control a Nafion-based IPMC-Li+ exposed to different relative humidities and electrical stimulis. The PI control system uses a camera with a machine vision application as a feedback sensor. Support instrumentation was developed to control the relative humidity, apply an electrical stimulus, and measure the electromechanical response. The pattern recognition algorithm implemented in the controller is efficient, with accuracy above 95%, making the feedback sensor reliable. Therefore, the PI controller was effective, stable, and capable of controlling and characterizing IPMC devices when relative humidity was above 60% at a low-frequency displacement and avoided the undesired back-relaxation phenomenon.

Abstract Ionomeric Polymer-Metal Composites (IPMC) are smart materials whose electromechanical behavior depends on the electrical stimulus intensity, membrane hydration level, and ionic migration. This paper investigates the effects of the voltage, relative humidity, and counterion type (Li+ and K+) on a Nafion-based IPMC performance. Instrumentation capable of applying an electrical stimulus and measuring the electromechanical response was developed. The ionic conductivity was obtained using Electrochemical Impedance Spectroscopy. Complementary SEM analyses were performed before and after actuation cycles. The IPMC performance improved when the electrical stimulus was 5.00 V, RH = 90%, and Li+ was used. The IPMC-Li sample is an excellent candidate to be used as an actuator since it exhibited fast actuation movement, considerable displacement, and no evident back-relaxation. However, its mechanical performance decreased over time because of a progressive increase in platinum electrode crack density and dehydration. The video analysis technique is an efficient, effective, and low-cost technique.

The ionomeric electroactive polymers-metal composites (IPMC) are materials that realize bending movements in response to an electrical stimulus and can be applied to the artificial muscles development. This paper investigated the influence of the hydration level on the electromechanical behavior of Nafion based IPMC. An experimental apparatus composed by a system to measure the bending force and to control the electrical stimulus and the relative humidity around the sample was developed. The main results indicated that samples with higher hydration level produce larger bending forces, but they show a more expressive back relaxation with lower time constant. A discussion about the results considering some models described in the literature conclude the paper.