Performance Of Ionic Polymer Metal Composite Research Articles

Fabrication and Characterization of a Novel Smart-Polymer Actuator with Nanodispersed CNT/Pd Composite Interfacial Electrodes.

As emerging smart polymers, ionic polymer-metal composites (IPMCs) are playing more and more important roles as promising candidates for next-generation actuators in terms of academic interest and industrial applications. It is reported that the actuation behaviors of IPMCs are dependent on the electrochemical kinetic process between metal/polymer interfaces to a great extent. Thus, the fabrication of tailored metal/polymer interface electrodes with large surface areas and superior interface characteristics is highly desirable in improving the actuation performance of IPMCs, which is still technologically critical for IPMCs. In this contribution, we developed a novel fabrication technology for carbon/metal composite electrodes with a superior interface structure and characteristics to optimize the actuation behaviors of IPMCs by exploiting the synergistic effect of combining a sulfonated multi-walled carbon nanotube (SCNT)/Nafion hybrid layer with nanodispersed Pd particles. The improved IPMCs showed significantly enhanced capacitance characteristics and highly facilitated charge–discharge processes. Moreover, their actuation behaviors were greatly improved as expected, including approximately 2.5 times larger displacement, 3 times faster deformation speed, 4 times greater output force, and 10 times higher volume work density compared to those of the IPMCs with traditional electrode structures. The advantages of the developed SCNT/Pd-IPMCs will greatly facilitate their applicability for artificial muscles.

Formation and characterization of Pt-Cu-IPMC with high specific surface area and dendritic electrode

ABSTRACT Ionic polymer–metal composite (IPMC) is a kind of electroactive intelligent material. The dendritically interfacial electrodes (DIEs) is very important to the performance of IPMC. Herein, the copper–platinum composite electrode (Pt-Cu-IPMC) with a high specific area DIEs was prepared by combining impregnation-reduction plating platinum (IRP-Pt), autocatalytic plating platinum (ACP-Pt) and chemical reduction plating copper (CRP-Cu). The effects of DIEs and the cycles of ACP-Pt have been systematically investigated on the electrode’s thickness, micro-morphology and electromechanical response characteristics of all samples. Importantly, when the cycles of ACP-Pt increases, the platinum and copper particles in the ionomer membrane are highly dispersed. For example, when the cycles of ACP-Pt is 4, the penetration depth of the DIEs reaches 31.98 µm. Thus, copper and platinum dendrites were clearly observed in the samples. Combined with the analysis of the strain energy density, it showed that the presence of DIEs has some impact on the driving performance of the IPMC, the tip displacement, and blocking force of 67.27 mm and 27.21 mN have been achieved in the Pt-Cu-IPMC after three cycles of ACP-Pt.

Preparation and performance analysis of Pt-IPMC for driving bionic tulip

Based on the biological characteristics of tulip, the low driving voltage and fast response of ionic polymer metal composite (IPMC), we analyzed the fabrication, morphology and performance of the platinum IPMC (Pt-IPMC) and selected the right IPMC for driving bionic tulip. The preparation and performance of IPMC was analyzed first in this paper such as blocking force, output displacement and bending angle of IPMC under the different directed current voltage (DC). The optimal IPMC sample size and driving voltage were selected based on tulip blooming angles and the strain energy density of IPMC, which completed the blooming process of bionic tulip. The feasibility of IPMC used in driving bionic field was fully proved in this paper, which laid a foundation for the application of IPMC in driving biomimetic biological robots.

A novel strategy to enhance the generating power of ionic polymer metal composites through magnetoelectricity

In this paper, we put forward a method to enhance the output power of ionic polymer metal composite (IPMC) through a magnetic field by combining the ion-electronic and magnetoelectric effects. Firstly, we confirmed that the total output voltage of IPMC deformation originates from the vector superposition of ion-electronic and magnetoelectric effects when applied a magnetic field. The open circuit voltage and output power of IPMC were experimentally investigated by adjusting the deflecting frequency and magnetic field intensity. As the frequency and magnetic field intensity increase, the increased voltage and output power caused by the magnetic field show an upward trend. Then, the experimental results were analyzed and verified through the piezoelectric and magnetoelectric theory. The results show that the increased voltage has a linear relationship with the frequency and magnetic field intensity and has nothing to do with the inherent parameters of IPMC itself. Finally, we performed simulation and practical tests to verify the energy harvesting effect of this strategy. During the energy harvesting test of water flow fluctuation, the open circuit voltage was increased by 41.91% and the output energy was increased by 110.03%, which indicates that this strategy has excellent performance in practical applications. By this study, the power generation performance of IPMC was explored and improved through multiple physical mechanisms.

Improving the torsion performance of IPMC by changing the electrode separation

Ionic polymer metal composites (IPMCs) are widely studied as actuators and sensors, due to their large bending motion, flexibility and being light-weight. Nowadays, IPMCs are used in the bionic field, for example, to achieve bending and twisting movements of wings and fins. In this paper, a method is proposed to optimize the torsion performance of IPMCs by changing the electrode separation. The IPMCs with patterned electrode fabricated by masking technique are proposed to accomplish twisting motion. The result indicates that the torsion performance is improved as the electrode separation increased. Thereby it provides a new strategy for the bionic field with twisting behavior.

Electroless copper deposition and interface characteristics of ionic electroactive polymer

In this study, the cheap copper electrode ionic polymer metal composite (IPMC) was prepared by chemical deposition. The formation mechanism of the copper electrode layer was analyzed firstly, then the surface and cross section morphology, roughness and porosity of IPMC were measured, and the interface profile was simulated and predicted based on Weierstrass-Mandelbrot (WM) function, at last, the adhesion force of the interface was calculated. The results show that the coarsening of Nafion and the adsorption of Ag+ ions provide a good catalytic activation site for the nucleation and rapid growth of copper particles. The copper layer on the surface of IPMC is arranged in granular, distributed compactly and uniformly, with the porosity of 52.3% and a strong (111) preferred orientation, which are beneficial to the performance of IPMC. Based on the WM function, the fractal dimension, characteristic scale and characteristic roughness are used to reflect the flatness and complexity of surface profile. The adhesive strength between the substrate and the coating is mainly due to the surface force field caused by the coarsening treatment. The theoretical and simulation studies of the interface characteristics are helpful to understand the internal mass transfer mechanism of IPMC and characterize the complex interface morphology, which also lays a foundation for the later research and application of IPMC.

Motion Control of Capsule-like Underwater Robot Utilizing the Swing Properties of Ionic Polymer Metal Composite Actuators

Ionic Polymer Metal Composite (IPMC) is a novel electrically actuated intelligent material with the advantages of big bending displacement, low driving voltage, flexible and so on. It has been recognized as one of the most attractive actuators with prospective applications for underwater robots and bionic organs. In this work, a capsule-like robot was introduced with the pectoral and caudal fins made of IPMC. By analyzing the properties of displacement response to square waves with different frequencies and low level voltages, it was found that performance of IPMC are frequency sensitive. Besides, when the absolute value of low level voltage decreases, IPMC could swing on one side with the decrease in amplitudes, whereas the amplitude at high level voltage fluctuates within small ranges at low frequencies. IPMC tip can approximately maintain when the frequency of driving signal around 30 Hz. Such properties were employed to control the locomotion of robot combining the motions of pectoral and caudal fin. Thus, the locomotions of swimming forward, turning and positioning were realized.

A Compact Review of IPMC as Soft Actuator and Sensor: Current Trends, Challenges, and Potential Solutions From Our Recent Work.

Recently, attempts have been made to develop ionic polymer–metal composite (IPMC), which is garnering growing interest for ionic artificial muscle, as a soft actuator and sensor due to its inherent properties of low weight, flexibility, softness, and particularly, its efficient transformation of electrical energy into mechanical energy, with large bending strain response under a low activation voltage. In this paper, we focused on several current deficiencies of IPMC that restrict its application, such as non-standardized preparation steps, relaxation under DC voltage, solvent evaporation, and poor output force. Corresponding solutions to overcome the abovementioned problems have recently been proposed from our point of view and developed through our research. After a brief introduction to the working mechanism of IPMC, we here investigate the key factors that influence the actuating performance of IPMC. We also review the optimization strategies in IPMC actuation, including those for preparation steps, additive selection for a thick casting membrane, solvent substitutes, water content, encapsulation, etc. With consideration of the role of the interface electrode, its effects on the performance of IPMC are revealed based on our previous work. Finally, we also discuss IPMCs as potential sensors theoretically and experimentally. The elimination of the deficiencies of IPMC will promote its applications in soft robotics.

Fabrication and performance of ionic polymer-metal composites for biomimetic applications

Ionic Polymer-Metal Composites (IPMCs) consisting of ionic polymer membrane sandwiched between platinum and copper (Cu-Pt) electrodes have been synthesized via electroless plating and electroplating. The tip displacement of Cu-Pt coated IPMC reached about 10.7 mm when a sinusoidal potential of 3V, 0.6Hz was applied through the membrane. The surface roughness of Pt coated IPMC, Cu-Pt coated IPMC and Cu-Pt coated IPMC after bending deformation tests were 1.21, 0.77 and 0.71 μm respectively, indicating that Cu electrode could reduce surface roughness. It was also found that a new generated Cu layer healed the cracks of Pt electrode, was formed through using voltage polarity. Butyl rubber and polydimethysiloxane (PDMS) were employed to encapsulate Cu-Pt coated IPMC to prevent Cu electrode from oxidation. The output deformation of packaged Cu-Pt coated IPMCs were stable under various amplitude of potential. The deflection of Cu-Pt coated IPMCs kept in air for 3, 7, 15 and 22 days respectively had no significant changes and were all about 10.1 mm by applying the potential of 3V, 0.6Hz, revealing that Cu electrode is durable and Cu-Pt coated IPMCs exhibit remarkable promise as biomimetic actuators.

The Effects of Dimensions on the Deformation Sensing Performance of Ionic Polymer-Metal Composites.

As an excellent transducer, ionic polymer-metal composites (IPMCs) can act as both an actuator and a sensor. During its sensing process, many factors, such as the water content, the cation type, the surface electrode, and the dimensions of the IPMC sample, have a considerable impact on the IPMC sensing performance. In this paper, the effect of dimensions focused on the Pd-Au typed IPMC samples with various thicknesses, widths, and lengths that were fabricated and their deformation sensing performances were tested and estimated using a self-made electromechanical sensing platform. In our experiments, we employed a two-sensing mode (both current and voltage) to record the signals generated by the IPMC bending. By comparison, it was found that the response trend was closer to the applied deformation curve using the voltage-sensing mode. The following conclusions were obtained. As the thickness increased, IPMC exhibited a better deformation-sensing performance. The thickness of the sample changed from 50 μm to 500 μm and corresponded to a voltage response signal from 0.3 to 1.6 mV. On the contrary, as the length increased, the sensing performance of IPMC decreased when subjected to equal bending. The width displayed a weaker effect on the sensing response. In order to obtain a stronger sensing response, a thickness increase, together with a length reduction, of the IPMC sample is a feasible way. Also, a simplified static model was proposed to successfully explain the sensing properties of IPMC with various sizes.

Enhancing the deformation range of ionic polymer metal composites through electrostatic actuation

The large range of deformations of ionic polymer metal composites (IPMCs) has often been proposed as a key advantage of these soft active materials. Nevertheless, many applications in soft robotics still cannot be addressed by current IPMC technology, demanding an even wider deformation range. Here, we empirically demonstrate the feasibility of integrating electrostatic actuation to enhance IPMC deformations. Through the use of external contactless electrodes, an electrostatic pressure is generated on the IPMC, thereby magnifying the deformation elicited by the small voltage applied across its electrodes. A mathematical model is established to predict the onset of the pull-in instability, which defines when electrostatic actuation can be effectively utilized to enhance IPMC performance.

Formation and Characterization of Dendritic Interfacial Electrodes inside an Ionomer.

Formation of dendritic interfacial electrodes (DIEs) between metal/polymer interfaces has high demands in a variety of areas. By combining impregnation electroplating (IEP) step with impregnation-reduction (IR) step under straightforward conditions, we report a novel method of preparation of dendritic interfacial metal electrodes of palladium, platinum, silver and copper inside an ionomer for ionic polymer-metal composites (IPMC) application. The depth of palladium DIEs can be controlled by adjusting the reaction time, and the maximum depth can almost reach up to contact from the both sides of ionomer with a total thickness of 200 μm. The capacitance and actuation performance of IPMC was dramatically enhanced because of the presence of DIEs.

Effects of surface roughening of Nafion 117 on the mechanical and physicochemical properties of ionic polymer–metal composite (IPMC) actuators

In this paper, the surface of a Nafion membrane was roughened by the sandblasting method, mainly considering the change of sandblasting time and powder size. The roughened surfaces were characterized in terms of their topography from the confocal laser scanning microscope (CLSM) and SEM. The key surface parameters, such as Sa (the arithmetical mean deviation of the specified surface profile), SSA (the surface area ratio before and after roughening) and the area measurement on the histogram from the CLSM images, were extracted and evaluated from the roughened membranes. Also, the detailed change in surface and interfacial electrodes were measured and discussed together with the surface resistance, equivalent modulus, capacitance and performances of IPMC actuators based on the roughened membranes. The results show that a suitable sandblasting condition, resulting in the decrease in the bending stiffness and the increase in the interface area closely related to the capacitance, can effectively increase the electromechanical responses of IPMCs. Although the surface roughening by sandblasting caused a considerable lowering of mechanical strength, it was very effective for enlarging the interfacial area between Nafion membrane and the electrode layers, and for forming a penetrated electrode structure, which facilitated improvement of the surface resistance and capacitance characteristics of IPMCs. In this work, a quantitative relationship was built between the topography of Nafion membrane surface and electromechanical performance of IPMCs by means of sandblasting.

Effect of surface roughening method on performance of IPMC artificial muscle

Ionic Polymer Metal Composite (IPMC) is a new kind of ionic Electro-active Polymer (EAP) composed of a perfluorinated polymer membrane coated with a noble metal (usually use Pt and Au) on both sides, which behaves like biological muscle bends towards the anode (in the case of cation exchange membrane) under the influence of an applied electric field. Since it has several advantages such as large deformation, light weight, flexibility, bio-compatibility and low driving voltage compared with shape memory alloy materials and piezoelectric ceramic, IPMC, also termed “artificial muscle”, can be widely applied to the actuators, sensors, biomimetic materials and medical engineering. As a kind of composite materials composed of polymer and metal, the performance of IPMC is closely related to the construction between polymer membrane and metal electrode. Surfaces roughening treatment of the Nafion membranes is employed in order to improve the construction way of the interfaces between polymer membranes and metal electrodes, which is a significant method to improve the electromechanical properties of IPMC materials. In this paper, a controllable and directional surface treatment for IPMC was developed. A surface roughening device included friction head, membrane jig and fixed stage was demonstrated for the IPMC membranes based on linear reciprocating motion of the UMT-2 friction-abrasion testing machine. Compared with manual surfaces roughening treatment, mechanical surface roughening treatments under 20, 50 and 80 N three kinds of load was used. The same preparation process was guaranteed to prepare IPMC on the basis of Nafion membranes with different surfaces roughening methods. The surface morphology of the Nafion membranes was observed using digital microscope. The cross-sectional and metal electrodes of the IPMC were observed using scanning electron microscopy (SEM). The surface roughness of the roughened membranes were measured with surface profiler. The effect of different roughening treatments methods and loading condition on the displacement and blocking force of IPMC artificial muscle were investigated using home-built apparatus. Compared with IPMC with manual surfaces roughening treatment, the IPMC with 20 N roughening load shows the best actuation performance of displacement, and the IPMC with 50 N roughening load shows the best actuation performance of blocking force. Mechanical roughening method can exclude the human factors in the manual roughening process, and produce controllable loading strength and direction, making the polishing cracks uniform in depths and directions. Compared with manual surfaces roughening treatment, the compactness constructed of the interfaces between polymer membranes and metal electrodes can be improved by the mechanical surface roughening treatments, the adsorption capability and deposition thickness of the Pt particles were increased. Thus, the flat and dense electrode with uniform cracks was obtained, which definitely reduced the surface resistance and enhance the blocking force and displacement of IPMC. The denser and thicker electrodes can prevent water leakage and extend the effective operating time of IPMC artificial muscle in the air. This research can improve the stability of the preparation process, which lays a solid foundation for the standardization of preparation process of IPMC. Also, the actuation performance of IPMC was enhanced, guaranteeing the further development and application of IPMC artificial muscle.

Electromechanical performance of ionic polymer-metal composite under electrode constraint

The electro-active performance of ionic polymer-metal composite has been widely reported to be related to the strain caused by the unbalance of local water content. In this paper, the anisotropic strain under electrode constraint in ionic polymer-metal composite during water uptake was investigated. A model was proposed to claim that existence of electrode would lead to anisotropic swelling in ionic polymer-metal composite, and the strain state was significantly affected by the electrode volume proportion as well as the elasticity ratio of the electrode and polymer. Based on Nafion-Pd ionic polymer-metal composite, experiments were carried out to measure the swelling strain during saturation process. Evaluation by the proposed model showed great agreement with the experimental observation, both of which gave the conclusion that, under the surface electrode constraint, strain in the thickness direction was much larger than that in plane directions. At last, based on a formerly-established multi-physical model, it was predicted that for ionic polymer-metal composite, the anisotropy of local swelling can lead to a 10%–15% decrease of the tip displacement.

Ionic polymer metal composites with polypyrrole-silver electrodes

Ionic polymer metal composites (IPMCs) are a class of soft active materials that are finding increasing application in robotics, environmental sensing, and energy harvesting. In this letter, we demonstrate the fabrication of IPMCs via in-situ photoinduced polymerization of polypyrrole-silver electrodes on an ionomeric membrane. The composition, morphology, and sheet resistance of the electrodes are extensively characterized through a range of experimental techniques. We experimentally investigate IPMC electrochemistry through electrochemical impedance spectroscopy, and we propose a modified Randle's model to interpret the impedance spectrum. Finally, we demonstrate in-air dynamic actuation and sensing and assess IPMC performance against more established fabrication methods. Given the simplicity of the process and the short time required for the formation of the electrodes, we envision the application of our technique in the development of a rapid prototyping technology for IPMCs.

Electroactive nanostructured polymer actuators fabricated using sulfonated styrenic pentablock copolymer/montmorillonite/ionic liquid nanocomposite membranes

High-bendable, air-operable ionic polymer–metal composite (IPMC) actuators composed of electroactive nanostructured middle-block sulfonated styrenic pentablock copolymer (SSPB)/sulfonated montmorillonite (s-MMT) nanocomposite electrolyte membranes with bulky imidazolium ionic liquids (ILs) incorporated were fabricated and their bending actuation performances were evaluated. The SSPB-based IPMC actuators showed larger air-operable bending displacements, higher displacement rates, and higher energy efficiency of actuations without conventional IPMC bottlenecks, including back relaxation and actuation instability during actuation in air, than the Nafion counterpart. Incorporation of s-MMT into the SSPB matrix further enhanced the actuation performance of the IPMC actuators in terms of displacement, displacement rate, and energy efficiency. The remarkably high performance of the SSPB/s-MMT/IL IPMCs was considered to be due to the microphase-separated large ionic domains of the SSPB (the average diameter of the ionic domain: ca. 20 nm) and the role of s-MMT as an ionic bridge between the ionic domains, and the ion pumping effect of the bulky imidazolium cations of the ILs as well. The microphase-separated nanostructure of the composite membranes caused a high dimensional stability upon swelling in the presence of ILs, which effectively preserved the original electrode resistance against swelling, leading to a high actuation performance of IPMC.

Effects of surface roughening on the mass transport and mechanical properties of ionic polymer-metal composite

Ionic Polymer-Metal Composite (IPMC) has been well-documented of being a promising functional material in extensive applications. In its most popular and traditional manufacturing technique, roughening is a key process to ensure a satisfying performance. In this paper, based on a lately established multi-physical model, the effect of roughening process on the inner mass transportation and the electro-active output of IPMC were investigated. In the model, the electro-chemical field was monitored by Poisson equation and a properly simplified Nernst–Planck equation set, while the mechanical field was evaluated on the basis of volume strain effect. Furthermore, with Ramo-Shockley theorem, the out-circuit current and accumulated charge on the electrode were bridged with the inner cation distribution. Besides, nominal current and charge density as well as the curvature of the deformation were evaluated to characterize the performance of IPMC. The simulation was implemented by Finite Element Method with Comsol Multi-physics, based on two groups of geometrical models, those with various rough interface and those with different thickness. The results of how the roughening impact influences on the performance of IPMC were discussed progressively in three aspects, steady-state distribution of local potential and mass concentration, current response and charge accumulation, as well as the curvature of deformation. Detailed explanations for the performance improvement resulted from surface roughening were provided from the micro-distribution point of view, which can be further explored for the process optimization of IPMC.

Encapsulation of ionic polymer-metal composite (IPMC) sensors with thick parylene: Fabrication process and characterization results

Ionic polymer-metal composites (IPMCs) tend to have inconsistent sensing properties when operating in air under different humidity levels, or after exposure to different ambient media. Motivated by the need to ensure consistent sensing performance of IPMCs under different ambient environments, in this paper we propose thick (up to 25 micrometers) parylene C coating for IPMC sensors, develop effective coating processes, and evaluate the performance of the encapsulated sensors, along with the comparison with the typical naked IPMC sensors. The proposed fabrication process features the water drive-in step which enables the control and adjustment of the hydration level of an encapsulated IPMC. Experiments are conducted to evaluate the sensing consistency of IPMC sensors in a humidity chamber, first under different humidity levels, and then following exposure to solutions with different cations and different organic solvents. Experimental results show that the proposed thick parylene coating can effectively keep the water content inside the IPMC, isolate the IPMC sensor from various ambient environments, and maintain the sensing consistency, which allows IPMC sensors to be used in practical applications.

Improving the performance of IPMCs with a gradient in thickness

An ionic polymer metal composite (IPMC) is a kind of electro-active polymer. Due to the properties of low driving voltage, large deformation, flexibility and lightness, it is becoming one of the more popular from a diversity of smart materials. In this study, a novel structure of Nafion® film is proposed to improve the performance of an IPMC. IPMC samples with a gradient structure in thickness are fabricated and their performance is investigated to confirm the validity of the gradient structure. The deformation displacement and the blocking force are compared under AC and DC voltage by experiments. The results indicate that the structure of gradient in thickness would improve the performance both in deformation displacement and blocking force.