Taeseon Hwang

Electromechanical performance and other characteristics of IPMCs fabricated with various commercially available ion exchange membranes

Ionic polymer–metal composites (IPMCs) are considered as some of the favorable candidates to be used as biomimetic actuators and sensors in an aqueous environment. Amongst all components that compose an IPMC, the ion exchange membrane is where hydrated cations migrate when an electric field is applied across the membrane and it eventually produces the deformation of the IPMC. Nafion® is the most commonly used ion exchange membrane. Many studies have been conducted on IPMCs made with Nafion®. In this study, three other commercially available ion exchange membranes were used to fabricate IPMCs and their performance as actuators was compared with IPMCs made with Nafion® membrane. Their potential for use in IPMC actuators was investigated by conducting various characterizations such as water uptake, ion exchange capacity, morphology, thermal property, blocking force and bending displacement.

A fabrication method of unique Nafion® shapes by painting for ionic polymer–metal composites

Ionic polymer–metal composites (IPMC) are useful actuators because of their ability to be fabricated in different shapes and move in various ways. However, producing unique or intricate shapes can be difficult based upon the current fabrication techniques. Presented here is a fabrication method of producing the Nafion® membrane or thin film through a painting method. Using an airbrush, a Nafion water dispersion is sprayed onto an acrylonitrile butadiene styrene surface with a stencil of the desired shape. To verify that this method of fabrication produces a Nafion membrane similar to that which is commercially available, a sample that was made using the painting method and Nafion 117 purchased from DuPont™ were tested for various characteristics and compared. The results show promising similarities. The painted Nafion sample was chemically plated with platinum and compared with a traditional IPMC for its displacement and blocking force capabilities. The painted IPMC sample showed comparable results.

Bioinspired travelling wave generation in soft-robotics using ionic polymer-metal composites

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 four-wing 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.

Modeling of a soft multiple-shape-memory ionic polymer-metal composite actuator

The multiple-shape-memory ionic polymer-metal composite (MSM-IPMC) actuator can demonstrate complex 3D deformation. The MSM-IPMC have two characteristics, which are the electro-mechanical actuation effect and the thermal-mechanical shape memory effect. The bending, twisting, and oscillating motions of the actuator could be controlled simultaneously or separately by means of thermal-mechanical and electro-mechanical transactions. In our study, we theoretically modelled and experimentally investigated the MSM-IPMC. We proposed a new physical principle to explain the shape memory behavior. A theoretical model of the multiple shape memory effect of MSMIPMC was developed. It is based on the assumption that the multiple shape memory effect is caused by the thermal stress and each individual Young’s modulus is ‘memorized’ during the previous programming process. As the MSM-IPMC was reheated to each temperature, the corresponding thermal stress was applied on the MSM-IPMC, and the Young’s modulus was recovered, which result in the shape recovery of the MSM-IPMC. To verify the model, a MSM-IPMC sample was prepared. Experimental tests of MSM-IPMC were conducted. By comparing the simulation results and the experimental results, both results have a good agreement. The current study is beneficial for the better understanding of the underlying physics of MSM-IPMC.

Programmable variable stiffness 2D surface design

Variable stiffness features can contribute to many engineering applications ranging from robotic joints to shock and vibration mitigation. In addition, variable stiffness can be used in the tactile feedback to provide the sense of touch to the user. A key component in the proposed device is the Biased Magnetorheological Elastomer (B-MRE) where iron particles within the elastomer compound develop a dipole interaction energy. A novel feature of this device is to introduce a field induced shear modulus bias via a permanent magnet which provides an offset with a current input to the electromagnetic control coil to change the compliance or modulus of a base elastomer in both directions (softer or harder). The B-MRE units can lead to the design of a variable stiffness surface. In this preliminary work, both computational and experimental results of the B-MRE are presented along with a preliminary design of the programmable variable stiffness surface design.

Property modification of nafion via polymer blending with polyimide (Conference Presentation)

The blended ion exchange membrane between Nafion and Polyimide (PI) was used for fabrication of the ionic polymer–metal composite (IPMC) not only to redeem inherent drawbacks of Nafion such as high cost or environment-unfriendliness but also to enhance mechanical properties of Nafion. PI solution was blended in Nafion solution by a volume ratio and membranes were prepared through solution casting method. The prepared blended Nafion membranes can be fabricated IPMCs with electroless plating of platinum electrode onto its surface. The surface resistance of all prepared IPMCs is measured through 2-point probe. This study investigated the chemical structure and mechanical properties of prepared blended membranes. Moreover, we characterized the cross-section morphology and studied the electromechanical performances (displacement and blocking force) of prepared IPMC actuators. The prepared IPMC actuators with blended Nafion membranes were demonstrated comparable electromechanical performance by significantly reducing the content of Nafion.

Producing intricate IPMC shapes by means of spray-painting and printing (Conference Presentation)

Ionic Polymer-Metal Composites (IPMC) are common soft actuators that are Nafion® based and plated with a conductive metal, such as platinum, gold, or palladium. Nafion® is available in three forms: sheets, pellets, and water dispersion. Nafion® sheets can be cut to the desired dimensions and are best for rectangular IPMCs. However, the user is not able to change the thickness of these sheets by stacking and melting because Nafion® does not melt. A solution to this is Nafion® pellets, which can melt. These can be used for extrusion and injection molding. Though Nafion® pellets can be melted, they are difficult to work with, making the process quite challenging to master. The last form is Nafion® Water Dispersion, which can be used for casting. Casting can produce the desired thickness, but it does not solve the problem of achieving complex contours. The current methods of fabrication do not allow for complex shapes and structures. To solve this problem, two methods are presented: painting and printing. The painting method uses Nafion® Water Dispersion, an airbrush, and vinyl stencils. The stencils can be made into any shape with detailed edges. The printing method uses Nafion® pellets that are extruded into filaments and a commercially available 3D printer. The models are drawn in a Computer-Aided Drawing (CAD) program, such as SolidWorks. The produced Nafion® membranes will be compared with a commercial Nafion® membrane through a variety of tests, including Fourier Transform Infrared Spectroscopy, Scanning Electron Microscope, Thermogravimetric Analysis, Dynamic Mechanical Analysis, and Optical Microscope.

Numerical and experimental investigation of a biomimetic robotic jellyfish actuated by Ionic Polymer-Metal Composite

A biomimetic jellyfish robot is explored. The robot will be actuated by Ionic Polymer-Metal Composites arranged in a silicone dome. Computational Analysis is used to optimize thrust production by the jellyfish robot. Preliminary experiments will be conducted to analyze the deformation, thrust, displacement, and velocity. The two analyses will be compared to further optimize the design.

Property modification of Nafion via polymer blending with ethylene vinyl alcohol "polyimide"(Conference Presentation)

The blended ion exchange membrane between Nafion and ethylene vinyl alcohol (EVOH) was used for fabrication of the ionic polymer–metal composite (IPMC) to redeem inherent drawbacks of Nafion such as high cost or environment-unfriendliness. EVOH solution was blended in Nafion solution by a volume ratio of 15 and 30 % membranes were prepared through solution casting method. The prepared blended Nafion membranes can be fabricated IPMCs with deposition of platinum electrode onto its surface without crack or delamination. The surface resistance of all prepared IPMCs is measured through 2 point probe. This study investigated the chemical structure and thermal properties of prepared membranes. Moreover, we characterized the cross-section morphology and studied the electromechanical performances (displacement and blocking force) of prepared IPMC actuators. The IPMC actuators with proposed blended Nafion membranes were demonstrated comparable electromechanical performance by significantly reducing the content of Nafion.

A fabrication method of unique Nafion shapes by painting for ionic polymer-metal composites(Conference Presentation)

Ionic Polymer-Metal Composites (IPMC) are useful actuators because of their ability to be fabricated in different shapes and move in various ways. However, the process to produce an IPMC is complicated and takes a few days. To make it possible to mass produce in any desired shape, the fabrication process must be updated. Presented here is a new way of producing the Nafion® base through a spraying method, then the electrode will be plated with spraying method as well. To verify that this method of fabrication produces a Nafion® sample similar to that which is commercially available, a sample that was made using spraying method and N117 purchased from DuPont™ were tested for various characteristics and compared.