The work presented in this paper introduces Aquivion as a potential candidate for additive manufacturing of ionomeric polymers for the application of IPMCs. First, Aquivion was characterized and compared with Nafion to show that it has the similar qualities, with the major difference being the ionic conductivity. Ionic polymer–metal composites (IPMCs) were fabricated using off-the-shelf membranes of Nafion and Aquivion. The actuation tests showed improved performance for an IPMC with Aquivion as the base compared to an IPMC with a Nafion base. With these results in mind, additive manufacturing of unique shapes using Aquivion filament was studied. A 3D printer was modified to work with Aquivion filament and the polymer was printed into various shapes. Using the printed membranes, IPMCs were fabricated using an electroless plating process. Nafion-based and printed Aquivion-based IPMCs were tested for their performance in back relaxation, frequency driven actuation, blocking force, and mechano-electric sensing. The printed Aquivion-based IPMCs performed comparably to Nafion-based IPMC in back relaxation and showed significantly improved performance in frequency driven actuation, blocking force generation, and mechano-electric sensing.

Ionic polymer-metal composites (IPMCs) are smart materials that exhibit large deformation in response to small applied voltages, and conversely generate detectable electrical signals in response to mechanical deformations. The study of IPMC materials is a rich field of research, and an interesting intersection of material science, electrochemistry, continuum mechanics, and thermodynamics. Due to their electromechanical and mechanoelectrical transduction capabilities, IPMCs find many applications in robotics, soft robotics, artificial muscles, and biomimetics. The current literature is sparce in multiphysics models that account for large deformations, coupled ion-solvent transport, the porous structure of the membrane, and lossy electrodes under finite-strains. This study addresses this by developing a new, hyperelastic porous media modeling framework for IPMCs using the principles of continuum thermodynamics and multiphasic materials. This framework compactly captures the broadest strokes of IPMC modeling methodologies, summarizing them in the form of general constitutive requirements placed on thermodynamic potential describing the polymer skeleton. A simple IPMC model is derived under this framework which captures the finite-strain deformation of a hyperelastic material, accounting for the coupled ion-solvent transport through the porous polymer, and resistive electrodes deforming with the skeleton. The resulting governing equations are further cast into a generalized nondimensional formulation, and an expansive set of unique dimensionless Π-groups are derived for IPMC actuator and sensor devices. This new framework and the nondimensional formulation lay the groundwork for future research and an expansive characterization of IPMC transduction phenomena via dimensional analysis.

A biomimetic underwater robot was designed utilizing ionic polymer-metal composite (IPMC) artificial muscles. The actuators were controlled by thermal and electrical inputs, taking advantage of both the shape-memory and electromechanical behavior of the material, to achieve multiple swimming modes in the proposed robot. The design was inspired by the pectoral fish swimming modes, such as stingrays, knifefish, and cuttlefish. The robot was actuated by two soft fins which consisted of multiple embedded IPMC actuators connected with an Eco-Flex membrane. Through electromechanical actuation, a traveling wave was generated on the soft fin. The deformation and the blocking force of the IPMCs on the fin were measured to characterize the actuators. An experimental setup was also designed in a flow channel to measure the thrust force of the robot under different frequencies and traveling wave numbers in a captive state. Experiments determined a peak thrusting force of 12 mN at a frequency of 0.5 Hz and wave number of 1, and twisting deformations of 30°were obtained. Additionally, shape-memory was utilized to change the swimming mode of the robot from Gymnotiform to Mobuliform. The designed underwater robot utilizes IPMC materials with multi-input control, enabling high deformability, with available maneuverability and agility in future studies.

Ionic polymer-metal composites (IPMCs) are one of many smart materials and have ionomer bases with a noble metal plated on the surface. The ionomer is usually Nafion, but recently Aquivion has been shown to be a promising alternative. Ionomers are available in the form of precursor pellets. This is an un-activated form that is able to melt, unlike the activated form. However, there is little study on the thermal characteristics of these precursor ionomers. This lack of knowledge causes issues when trying to fabricate ionomer shapes using methods such as extrusion, hot-pressing, and more recently, injection molding and 3D printing. To understand the two precursor-ionomers, a set of tests were conducted to measure the thermal degradation temperature, viscosity, melting temperature, and glass transition. The results have shown that the precursor Aquivion has a higher melting temperature (240 °C) than precursor Nafion (200 °C) and a larger glass transition range (32–65 °C compared with 21–45 °C). The two have the same thermal degradation temperature (~400 °C). Precursor Aquivion is more viscous than precursor Nafion as temperature increases. Based on the results gathered, it seems that the precursor Aquivion is more stable as temperature increases, facilitating the manufacturing processes. This paper presents the data collected to assist researchers in thermal-based fabrication processes.

Polyvinyl chloride (PVC) gels are soft electroactive polymers (EAPs) being researched for soft robotic applications. Sensing properties of these EAPs have not been investigated in detail in regard to fundamental mechanoelectrical transduction behavior, but this smart material has been shown to exhibit a detectable response to external stimuli. This study shows PVC gels to be an extremely sensitive material when undergoing mechanoelectrical transduction and explores some response dependencies and proposes a theoretical framework for mechanoelectrical transduction within the gel. The work presented here also uncovers a very interesting phenomena under extremely low compressive loads during the initial contact with the gel. This phenomenon is attributed to a surface tension creeping motion onto the loading surface with an accompanying polarity inversion in the sensing signal relative to fully loaded gels in compression. Experimental work on hysteresis was also completed showing very little memory in steady state mechanoelectrical response to repeated stepped loading cycles. This study demonstrates the mechanoelectric ability of PVC gels to perform in sensing experiments and acts as a fundamental framework to further broaden the applications of PVC gel sensors.

In this article, we present recent advancements in Ionic Polymer-Metal Composite (IPMC) technology. The current trajectory of the research shows immense promise for a future with highly capable IPMC actuators and sensors being used in a wide range of robotic, soft-robotic, and biomimetic technologies..

Biology inspired inventions have been of great interest to the researcher and engineer. Biomimicry offers special insight into nature's methods of motion control, with significance in thrust and drag control for swimming and flying lifeforms. An array of actuators designed in an artificial wing could be used to control aerodynamic effects to adjust drag or lift according to given wind conditions for improved flight, or to control stability prior to touchdown for a smooth landing, providing an additional means of aerodynamic stability control. In this study, a method of generating a travelling wave motion in attempt to mimic that observed in the wings of flying-fish (Exocoetidae) during descent are presented. Ionic polymer-metal composite actuators were arranged in an array and oscillated in a travelling wave motion. The arrays were held rigid between glass slides and embedded into a flexible substrate to create the soft ''wing'' surface for free-end displacement measurements. Using a microcontroller and motor drivers, a controllable travelling wave motion was created. Additionally, an array of actuators was connected to a 3D printed wing skeleton based on the dimensions of a fourwing flying-fish like structure. The results indicate the travelling wave motion can be controlled with ionic polymer-metal composite actuators as arranged in several configurations. This offers an experimental platform for further study of the aerodynamic effects of a travelling wave across a wing during flight.

No abstract