Il-Seok Park

Mechanical and thermal behavior of ionic polymer?metal composites: effects of electroded metals

In this study, we investigated the mechanical properties of various types of ionic polymer–metal composites (IPMCs) and Pt, Au, Pd, and Pt electroded ionic liquid (IL-Pt) IPMCs, by testing tensile modulus and dynamic mechanical behavior. The SEM was utilized to investigate the characteristics of the doped electroding layer, and the DSC was probed in order to look into the thermal behavior of various types of IPMCs. Au IPMCs, having a 5–7 µm-doped layer and nanosized Au particles (ca. 10 nm), showed the highest tensile strength (56 MPa) and modulus (602 MPa) in dried conditions. With regards to thermal behavior, Au IPMC had the highest Tg (153 °C) and Tm (263 °C) in both the DMA and DSC results. The fracture behavior of various types of IPMCs followed the behavior of the base material, Nafion™, which is represented as the semicrystalline polymer characteristic.Corrections were made to the caption of figure 6 on 18 June 2007. The corrected electronic version is identical to the print version.

Visualization of the cation migration in ionic polymer-metal composite under an electric field

Ionic polymer-metal composites (IPMCs) exhibit a large dynamic bending deformation due to the redistribution of counter-ions inside the polymer. It has not been possible to get the high resolution data of the cation migration. The images obtained so far have only validated the versatile actuation model. The actuation model states that the electrically induced cation movement contributes to the volumetric stress change in the membrane. In this work, a visualization of the cation migration using the fluorescent microscopy is created. The results demonstrated in this letter help to understand the underlying mechanism of the IPMC transduction.

Modeling and experiment of a muscle-like linear actuator using an ionic polymer?metal composite and its actuation characteristics

IPMC (ionic polymer?metal composite) actuators produce large bending displacements under low input voltages and are flexible enough to be implemented for biological and/or biomimetic applications. In this study, IPMC was considered for the development of a natural muscle-like linear actuator. For the purpose of design, numerical analysis was utilized to predict free strain and blocked stress of IPMC-based linear actuators, which we considered as the important parameters of a muscle-like actuator. An elementary unit composed of an IPMC and the base polymer, NafionTM, was proposed for an effective linear actuator. In order to find an optimal design and evaluate the actuation characteristics of the proposed elementary unit, actuation displacement and force were numerically calculated. The calculated maximum free strain of the optimal elementary unit was 25% under an applied 2?V input. Also, brief experimental results are provided.

Electrospun nanoscale polyacrylonitrile artificial muscle

Ionic polymer gels have been known to change in volume due to external stimuli. Activated polyacrylonitrile (PAN) fibers are known to contract and elongate more than 100% in length when immersed in caustic and acidic solutions, respectively. Commercially available PAN fibers with diameters in the range of tens of micrometers have been used in previously reported work. Instead, here we tried to study the phenomenon in fibers with diameters of a few hundred nanometers (Dp<1 µm). These nanometer sized fibers are expected to have faster response times when compared to commercially available fibers. Submicron diameter PAN fibers were made by electrospinning. The fibers were placed in a solution and the change in the shape of the fibers was observed with change in pH. The fibers contracted in acidic solution and expanded in basic solution similarly to reports in the literature. In this work, we measured the in situ variation in the diameter of the fibers using an environmental scanning electron microscope (E-SEM) and an atomic force microscope (AFM) while the change in pH was taking place. It appears that a variation of more than 100% was observed, similar to that observed with conventional fibers of diameter ranging from 10 to 50 µm. Also, the differential scanning calorimetry (DSC) results clearly provide the phase transition information regarding the contraction/elongation of such PAN fibers. These results provide the potential for developing fast actuating PAN muscles and linear actuators, and muscle structures similar to sarcomere/myosin/actin assembly.

Self-oscillating electroactive polymer actuator

To drive the electroactive polymer (EAP) materials and subsequently control their strain generation, the need for power electronics and driving circuits has been eminent. In this letter the authors demonstrate a spontaneous actuation of an electroactive polymer that requires only dc power to produce its ac responses. Such a dc-to-ac response of the EAP was achieved by the deposition of an effective electrocatalyst, i.e., platinum, on an ionomer, Nafion™. The coated ionomer was immersed into an acidic formaldehyde solution. An applied dc voltage will produce current oscillations in the system, and therefore oscillating bending of the actuator.

The mechanical properties of ionic polymer-metal composites

In this study, we investigated the mechanical properties of various type ionic polymer-metal composites (IPMCs) and Pt, Au, Pd, and Pt electroded ionic liquid (IL-Pt) IPMCs, by testing tensile modulus and dynamic mechanical behavior. The SEM was utilized to investigate the characteristics of the doped electroding layer, and the DSC was probed in order to look into the thermal behavior of various types of IPMCs. Au IPMCs, having a 5~7 &mgr;m doped layer and nano-sized Au particles (ca. 10 nm), showed the highest tensile strength (56 MPa) and modulus (602 MPa) in a dried condition. In a thermal behavior, Au IPMC has the highest Tg (153°C) and Tm (263°C) in both the DMA and DSC results. The fracture behavior of various types IPMCs followed base materials behavior, NafionTM, which is represented as the semicrystalline polymer characteristic.

IPMC-assisted miniature disposable infusion pumps with embedded computer control

For military applications, the availability of safe, disposable, and robust infusion pumps for intravenous fluid and drug delivery would provide a significant improvement in combat healthcare. To meet these needs, we have developed a miniature infusion prototype pump for safe and accurate fluid and drug delivery that is programmable, lightweight, and disposable. In this paper we present techniques regarding inter-digitated IPMCs and a scaleable IPMC that exhibits significantly improved force performance over the conventional IPMCs. The results of this project will be a low cost accurate infusion device that can be scaled from a disposable small volume liquid drug delivery patch to disposable large volume fluid resuscitation infusion pumps for trauma victims in both the government and private sectors of the health industry.

Sulfonated Polyamide Based IPMCs

In this study, we introduce a newly developed Ionic Polymer-Metal Composite (IPMC) family that is manufactured using a novel ionic exchange membrane-a randomly sulfonated fluoropoly(ether amide) (TFIPA-90)-as the base material. The thermal behavior and mechanical properties of the ionic polymer were probed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Electrochemical properties and the actuation performance of the TFIPA-90 based IPMCs were also investigated in this study. The stiffness of the TFIPA polymer was significantly higher than that of Nafion® and much noted at high temperatures (>100 oC). The thermal behavior of the TFIPA polymer also showed better stability than Nafion(R) at high temperatures due to the more rigid chemical structure of the ionomer. As an actuator, a new IPMC prepared from TFIPA-90 showed improved performance with rapid response time to the electric field and a large bending displacement. The TFIPA-based IPMC may be useful for microwave-driven robotic applications.

Multi-fields responsive ionic polymer-metal composites

The multi-fields responsive ionic polymer-metal composites, which have wide applications such as actuators, sensors and dampers in one body, are synthesized through an in-situ standard ion-exchange method using Ni particles doped on a NafionTM film. SEM, EDS, and XRD were utilized for revealing their crystal shape and type. Also dynamic mechanical analysis, vibrating sample magnetometry, and cyclic voltammetry were used to investigate the mechanical, magnetic, and electrical properties of the Ni doped ionic polymer-metal composites. The nano-sized Ni particles (ca. 300 nm) were synthesized on the NafionTM film with 2.5 μm layer. The Ni doped ionic polymer-metal composites demonstrated good magnetic, electric and electro-mechanical responses.

Porous Metal Hydride (PMH) Compacts for Thermal Energy Applications

Pelletized Porous Metal Hydride (PMH) was investigated in order to assess its thermal capability for energy storage/transfer applications. Metal hydrides have been known as promising materials for hydrogen storage systems, heat storage systems, and thermal devices, thanks to their nearly reversible reaction characteristics during the hydrogen absorbing and desorbing processes. The conventional powder-type metal hydrides however have a relatively low thermal conductivity, which is responsible for low heat generation. In the present study three representative metal hydrides, LaNi5 , Ca0.6 Mm0.4 Ni5 , and LaNi4.75 Al0.25 , metal hydride powders were coated with thin copper and pressed at 3,000 psig with metal additives in order to improve the thermal conductivity. This pelletizing process does not require the use of an organic binder and additional processes such as sintering under high pressure. The pelletized PMH compacts employing the copper coating exhibit higher thermal conductivity compared to raw metal hydride powders. However, pelletizing may deteriorate the permeability of the PMH compacts, lowering mass transfer of hydrogen. Therefore, the permeability must be observed to verify whether it meets the required level for suitable applications. Measurements were performed by varying copper fractions and plotted against the upstream/downstream pressure differential. Darcy’s equation in conjunction with an ideal gas assumption was used to calculate the permeability of a rigid wall design. This investigation reveals that rising copper content is accompanied with decreases in permeability. Permeability values for most samples tested in this study were found to be larger than the desirable level, 5 × 10−15 m2 . Additionally, the thermal performance of the LaNi5 PMH compacts was tested by calculating and comparing the heat generation of the PMH pellets and powders filled reactors during the hydrogen absorption process in water bath medium.Copyright