Kwang J. Kim

Ionic polymer-metal composites: I. Fundamentals

This paper, the first in a series of four review papers, presents a brief summary of the fundamental properties and characteristics of ionic polymeric-metal composites (IPMCs) as biomimetic sensors, actuators and artificial muscles. The forthcoming three review papers, to follow this paper, will address in detail such fundamentals and, in particular, manufacturing techniques and the electronic and electromechanical characteristics of IPMCs (part II), the phenomenological modelling of the underlying sensing and actuation mechanisms in IPMCs (part III) and the potential application areas for IPMCs (part IV). This paper is a summary of all recent findings and current state-of-the art manufacturing techniques, phenomenological laws and mechanical and electrical characteristics. A number of methodologies in developing high-force-density IPMCs are also reported.

Ionic polymer-metal composites: IV. Industrial and medical applications

This paper, the last in a series of four review papers to appear in this journal, presents some critical applications using ionic polymer?metal composites?(IPMCs). Industrial and biomedical applications of IPMCs are identified and presented along with brief illustration.

Ionic polymer–metal composites: II. Manufacturing techniques

This paper, the second in a series of four review papers to appear in this journal, presents a detailed description of various techniques and experimental procedures in manufacturing ionic polymer–metal composites (IPMCs) that, if fully developed, can be used as effective biomimetic sensors, actuators and artificial muscles as well as fully electroded with embedded electrodes for fuel cells. The performance of IPMCs manufactured by different manufacturing techniques are presented and compared. In particular, a number of issues such as force optimization using the Taguchi design of experiment technique, effects of different cations on electromechanical performance of IPMCs, electrode and particle size and distribution control, manufacturing cost minimization approaches, scaling and three-dimensional (3D) muscle production issues and heterogeneous composites by physical loading techniques are also reviewed and discussed.

Ionic polymer–metal composites: III. Modeling and simulation as biomimetic sensors, actuators, transducers, and artificial muscles

This paper, the third in a series of four review papers to appear in this journal, presents a number of descriptions of various modeling and simulation techniques and, briefly, the associated experimental results in connection with ionic polymer–metal composites and, in general, ionic polymer–conductor composites, as soft biomimetic distributed sensors, actuators, transducers, and artificial muscles.

Metal hydride compacts of improved thermal conductivity

Abstract Metal hydrides begin as hydride-forming metal alloys with good thermal conductivity. However, undergoing hydriding/dehydriding reactions and subsequently causing large strain changes, they decrepitate and finally form a powder bed. Such a powder bed exhibits poor thermal conductivity (k eff ∼0.1 W / m K ) and reduces the heat transfer process to and from the bed that occurs with hydrogen absorption and desorption. A newly developed technique reported here (recompressed expanded graphite technique), that allows one to significantly improve the thermal conductivity of a metal hydride, LaNi5, is presented. The compacts with LaNi5 and recompressed expanded graphite were made and their thermal conductivity measurements were taken. Recompressed expanded graphite is used to allow good heat transfer while providing efficient mass transfer. This study reports that the manufactured metal hydride compact has the thermal conductivity in the range of keff∼3– 6 W / m K that shows a greater potential in developing high-power metal hydride devices. It should be pointed out that a minute amount of expanded graphite increases the thermal conductivity of metal hydride significantly.

Ionomeric electroactive polymer artificial muscle for naval applications

Specialized propulsors for naval applications have numerous opportunities in terms of research, design, and fabrication of an appropriate propulsor. One of the most important components of any propulsor is the actuator that provides the mode of locomotion. ionomeric electroactive polymer may offer an attractive solution for locomotion of small propulsors. A common ionomeric electroactive polymer, ionic polymer-metal composites (IPMCs) give large true bending deformations under low driving voltages, operate in aqueous environments, are capable of transduction, and are relatively well understood. IPMC fabrication and operation are presented to further elucidate the use of the material for a propulsor. Various materials, including IPMCs, are investigated and a simplified propulsor model is explored.

An Equivalent Circuit Model for Ionic Polymer-Metal Composites and their Performance Improvement by a Clay-Based Polymer Nano-Composite Technique

Ionic Polymer-Metal Composite (IPMC) is a new class of polymeric material exhibiting large strain with inherent soft actuation. The observed motion characteristics of an IPMC subjected to an electric field is highly nonlinear. This is believed to be due primarily to the particle electrodes on the IPMC surface, which is inherently both capacitive and resistive due to particle separation and density. Knowing that the value of resistivity and capacity can be manipulated by the number of metal platings applied to the IPMC, the force response of an IPMC when subjected to an imposed electric field is due to the interaction of an array of capacitors and resistors along with ionic migration. In this effort we attempt to incorporate a capacitive and resistive model into the linear irreversible thermodynamic model. The advantages of using such a model are (i) the possible dynamic predictability of the material itself in connection with capacitive responses; and (ii) the realization of capacitive and resistive effect arising from the particle electrodes and the base polymer, respectively. The behavior of the proposed model can explain typical experimentally obtained values well. Also, an experimental effort to improve the properties of the base polymer was carried out by a novel nanocomposite technique. The experiment results on the current/voltage (I/V) curves indicate that the starting material of ionic polymer-metal composites (IPMCs) can be optimized to create effective polymer actuators.

An artificial muscle actuator for biomimetic underwater propulsors

In this paper, we introduce the analytical framework of the modeling dynamic characteristics of a soft artificial muscle actuator for aquatic propulsor applications. The artificial muscle used for this underwater application is an ionic polymer-metal composite (IPMC) which can generate bending motion in aquatic environments. The inputs of the model are the voltages applied to multiple IPMCs, and the output can be either the shape of the actuators or the thrust force generated from the interaction between dynamic actuator motions and surrounding water. In order to determine the relationship between the input voltages and the bending moments, the simplified RC model is used, and the mechanical beam theory is used for the bending motion of IPMC actuators. Also, the hydrodynamic forces exerted on an actuator as it moves relative to the surrounding medium or water are added to the equations of motion to study the effect of actuator bending on the thrust force generation. The proposed method can be used for modeling the general bending type artificial muscle actuator in a single or segmented form operating in the water. The segmented design has more flexibility in controlling the shape of the actuator when compared with the single form, especially in generating undulatory waves. Considering an inherent nature of large deformations in the IPMC actuator, a large deflection beam model has been developed and integrated with the electrical RC model and hydrodynamic forces to develop the state space model of the actuator system. The model was validated against existing experimental data.

Second law analysis and optimization of a combined triple power cycle

In this investigation, a combined triple (Brayton/Rankine/Rankine)/(gas/steam/ammonia) power cycle is analyzed. In the triple cycle, the exhaust of the Brayton gas topping cycle is used in a heat recovery steam generator (HRSG) to produce steam for a Rankine steam middle cycle followed by an ammonia Rankine bottoming cycle. The ammonia bottoming cycle provides a practical and more efficient hot and cold streams thermal matching for the triple cycle HRSG as compared to the HRSG of a conventional combined power cycle. Through exergy analysis of the cycle, the exergy of the exhaust streams and the irreversibility of each component in the cycle are determined, using reasonably practical constraints for the system components. These constraints are mainly due to the size of components and are conveniently parameterized and analyzed. The triple cycle was analyzed and optimized with respect to important system parameters, such as the gas topping cycle pressure ratio, gas turbine inlet temperature, HRSG pinch point, gas/steam approach temperature difference, rate of steam injection into combustion chamber and the effectiveness of the heat exchangers. One goal of the study is to find what configuration will achieve a thermal efficiency of 60% when reasonably practical constraints for system parameters are used.

Sulfur and Nitrogen Co‐Doped Graphene Electrodes for High‐Performance Ionic Artificial Muscles

UNLABELLED Sulfur and nitrogen co-doped graphene electrodes for bioinspired ionic artificial muscles, which exhibit outstanding actuation performances (bending strain of 0.36%, 4.5 times higher than PEDOT PSS electrodes, and 96% of initial strain after demonstration over 18 000 cycles), provide remarkable electro-chemo-mech anical properties: specific capacitance, electrical conductivity, and large surface area with mesoporosity.