Study of the Influence of the Hydration Level on the Electromechanical Behavior of Nafion Based Ionomeric Polymer-metal Composites Actuators

Abstract

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.

Electromechanical Evaluation of Ionomeric Polymer-Metal Composites Using Video Analysis

“…The used instrumentation was based on Hirano's et al 27 system with some adaptations. It consists of a National Instruments NI-9263 electrical signal generation and a NI-9218 data acquisition platforms, a Texas Instruments (TI) voltage and current amplifier (OPA551), an Arduino-monitored humidity system, an acrylic chamber, and an external digital camera (Sony RX100 IV).…”

PI Controller for IPMC Actuators Based on Nafion®/PT Using Machine Vision for Feedback Response at Different Relative Humidities

“…After reaching the maximum displacement value, the controller reduces the applied voltage to 0.0 V (Figure 9a). However, as the RH is very low, few H 2 O molecules are inside the membrane 31 . Consequently, the ionic migration in the opposite direction is very slow, so the device takes a long time to return to the desired position.…”

“…Other phenomena are also observed, such as backrelaxation (drawback associated with water counter diffusion, which causes the IPMC to shift in the opposite direction after maintaining a bias for a while) 23,31 , electrolysis (a reaction that splits water into hydrogen and oxygen) 32 , hysteresis (tendency to conserve their properties in the absence of the stimulus that generated them) 33 , and highly uncertain 34 . In other words, these devices have variations and instabilities in electromechanical performance, exhibiting nonlinearities and time-varying behaviors 35 .…”

Behavior of conducting polymer-based micro-actuators under a DC voltage

“…Redistribution of the cations and the adjacent water molecules occurs when a voltage is applied, which is generally regarded as the key physical driver of IPMC actuation [3] [4]. Back-relaxation is described in several studies for a range of material compositions (cation and solvent type) and experimental conditions such as the degree of hydration, applied voltage, and in-air versus in-solvent testing [5][6] [7][8] [9][10] [11] [12][13] [14] [15] [16] [17]. The composite bends to the anode side, for example, and gradually bends back to the cathode side while still under an electric potential.…”