Advanced Electro-active Dry Adhesive Actuated by an Artificial Muscle Constructed from an Ionic Polymer Metal Composite Reinforced with Nitrogen-doped Carbon Nanocages

An advanced electro-active dry adhesive, which was composed of a mushroom-shaped tibrillar dry adhesive array actuated by an Ionic Polymer Metal Composite （IPMC） artificial muscle reinforced with nitrogen-doped carbon nanocages （NCNCs）, was developed to imitate the actuation of a gecko＇s toe. The properties of the NCNC-reinforced Nation membrane, the electro- mechanical properties of the NCNC-reinforced IPMC, and the related electro-active adhesion ability were investigated. The NCNCs were uniformly dispersed in the 0.1 wt% NCNC/Nafion membrane, and there was a seamless connection with no clear interface between the dry adhesive and the IPMC. Our 0.1 wt% NCNC/Nation-IPMC actuator shows a displacement and force that are 1.6 - 2 times higher than those of the recast Nafion-IPMC. This is due to the increased water uptake （25.39%） and tensile strength （24.5 MPa） of the specific 3D hollow NCNC-reinforced Nation membrane, as well as interactions between the NCNCs and the sulfonated groups of the Nation. The NCNC/Nation-IPMC was used to effectively actuate the mushroom-shaped dry adhesive. The normal adhesion forces were 7.85 raN, 12.1 mN, and 51.7 mN at sinusoidal voltages of 1.5 V, 2.5 V, and 3.5 V, respectively, at 0.1 Hz. Under the bionic leg trail, the normal and shear forces were approximately 713.5 mN （159 mN·cm^-2） and 1256.6 mN （279 mN·cm^-2）, respectively, which satisfy the required adhesion. This new electro-active dry adhesive can be applied for active, distributed actuation and flexible grip in robots.

Review on Improvement,Modeling,and Application of Ionic Polymer Metal Composite Artificial Muscle

Recently,researchers have concentrated on studying ionic polymer metal composite(IPMC)artificial muscle,which has numerous advantages including a relatively large strain under low input voltage,flexibility,high response,low noise,light weight,and high driving energy density.This paper reports recent developments in IPMC artificial muscle,including improvement methods,modeling,and applications.Different types of IPMCs are described,along with various methods for overcoming some shortcomings,including improvement of Nafion matrix membranes,surface preparation of Nafion membranes,the choice of high-performing electrodes,and new electro-active polymers for enhancing the properties of IPMCs.IPMC models are also reviewed,providing theoretical guidance for studying the performance and applications of IPMCs.Successful applications such as bio-inspired robots,opto-mechatronic systems,and medical engineering are discussed.

Effects of Cu^2＋ Counter Ions on the Actuation Performance of Flexible Ionic Polymer Metal Composite Actuators

The resistance of Ionic Polymer Metal Composite （IPMC） electrodes plays an important role in the actuation performance of IPMC actuators. Owing to crack formation on the surface of platinum electrode, the surface resistance of the electrode increases, which greatly limits its actuating performance. In this paper, we proposed a new method of dynamic self-repair electrodes by ex- changing Cu2＋ into the IPMC basement membrane. IPMC actuators with Cu2＋ were prepared and the actuation performance in the air was subsequently measured. Compared with conventional IPMC actuators containing Li＋ counter ions, those containing Cu2＋ counter ions exhibited 2 times - 3 times larger displacement and 2 times -3 times bigger blocking force. In the morphology observation, we found that many small copper particles scattered in the middle of cracks after several bending cycles, which leads to an obvious decrease in electrode resistance. In the Cyclic Voltammetry （CV） scan measurement, we observed that the oxidation reaction of copper alternates with reduction reaction of copper ions with the change of voltage polarity, which was a dynamic process. Based on these analyses, it is concluded that the presence of Cu2＋ can repair the damaged electrodes and induce lower electrode resistance, thus leading to the performance improvement of actuation.

Printing ionic polymer metal composite actuators by fused deposition modeling technology

In this work,we printed a Nafion precursor membrane by fused deposition modeling(FDM)rapid prototyping technology and further fabricated IPMCs by electroless plating.The ion-exchange capacity of the Nafion membrane was tested,and the morphology of IPMCs was observed.The electro-mechanical properties of IPMCs under AC voltage inputs were studied,and grasping experiments were performed.The results show that the Nafion membrane after hydrolysis has a good ion-exchange ability and water-holding capacity.SEM observed that the thickness of the IPMC’s electrode layer was about 400 nm,and the platinum layer was tightly combined with the substrate membrane.When using a square wave input of 3.5 V and 0.1 Hz,the maximum current of IPMCs reached 0.30 A,and the displacement and blocking force were 7.57 mm and 10.5 mN,respectively.The new fabrication process ensures the good driving performance of the printed IPMC.And two pieces of IPMCs can capture the irregular objects successfully,indicating the feasibility of printing IPMCs by FDM technology.This paper provides a new and simple method for the fabrication of three-dimensional IPMCs,which can be further applied in flexible grippers and soft robotics.

Experimental study and electromechanical model analysis of the nonlinear deformation behavior of IPMC actuators

This paper develops analytical electromechanical formulas to predict the mechanical deformation of ionic polymer-metal composite (IPMC) cantilever actuators under DC excitation voltages. In this research, IPMC samples with Pt and Ag electrodes were manufactured, and the large nonlinear deformation and the effect of curvature on surface electrode resistance of the IPMC samples were investigated experimentally and theoretically. A distributed electrical model was modified for calculating the distribution of voltage along the bending actuator. Then an irreversible thermodynamic model that could predict the curvature of a unit part of an IPMC actuator is combined with the electrical model so that an analytical electromechanical model is developed. The electromechanical model is then validated against the experimental results obtained from Pt- and Ag-IPMC actuators under various excitation voltages. The good agreement between the electromechanical model and the actuators shows that the analytical electromechanical model can accurately describe the large nonlinear quasi-static deflection behavior of IPMC actuators.

Significantly Enhanced Actuation Performance of IPMC by Surfactant-Assisted Processable MWCNT/Nafion Composite

The performance of Ionic Polymer Metal Composite （IPMC） actuator was significantly enhanced by incorporating surfactant-assisted processable Multi-Walled Carbon Nanotubes （MWCNTs） into a Nation solution. Cationic surfactant Cetyl Trimethyl Ammonium Bromide （CTAB） was employed to disperse MWCNTs in the Nation matriX, forming a homogeneous and stable dispersion ofnanotubes. The processing did not involve any strong acid treatment and thus effectively preserved the excellent electronic properties associated with MWCNT. The as-obtained MWCNT/Nafion-IPMC actuator was tested in terms of conductivity, bulk and surface morphology, blocking force and electric current. It was shown that the blocking force and the current of the new IPMC are 2.4 times and 1.67 times higher compared with a pure Nation-based IPMC. Moreover, the MWCNT/IPMC performance is much better than previously reported Nafion-IPMC doped by acid-treated MWCNT. Such significantly improved performance should be attributed to the improvement of electrical property associated with the addition of MWCNTs without acid treatment.

The Development of a Venus Flytrap Inspired Soft Robot Driven by IPMC

In recent years,more and more creatures in nature have become the source of inspiration for people to study bionic soft robots.Many such robots appear in the public’s vision.In this paper,a Venus flytrap robot similar to the biological Venus flytrap in appearance was designed and prepared.It was mainly cast by Polydimethylsiloxane(PDMs)and driven by the flexible material of Ionic Polymer Metal Composites(IPMCs).Combining with ANSYS and related experiments,the appropriate voltage and the size of IPMC were determined.The results showed that the performance of the Venus flytrap robot was the closest to the biological Venus flytrap when the size of IPMC length,width and driving voltage reach to 3 cm,1 cm and 5.5 V,respectively.Moreover,the closing speed and angle reached 8.22°/s and 37°,respectively.Finally,the fly traps also could be opened and closed repeatedly and captured a small ball with a mass of 0.3 g firmly in its middle and tip.

Modeling of IPMC Cantilever＇s Displacements and Blocking Forces

The motion of an Ionic Polymer Metal Composite （IPMC） cantilever under a periodic voltage control is modeled. In our finite element 3D model, we follow both the free tip displacements and the blocking forces for various thicknesses and elastic constants of the ionomer membrane. It turns out that the maximum displacement of the free tip strongly depends on the value of the Young＇s modulus of the electrodes. Furthermore, the maximum blocking force, Fmax, increases with the thickness of the ionomer membrane. At constant values of Young＇s moduli of the electrodes and ionomer membrane thickness, if the Young＇s modulus of the ionomer membrane varies within the range from 0.2 MPa to 1 GPa, the change of Fmax is less than 10 %. The simulated maximal displacements, blocking forces and electrical currents are compared with the corresponding sets of ex- perimental data, respectively. Qualitative agreement between the simulated and the respective measured data profiles is ob- tained. Furthermore, it is found that the assumption of electrostatic interactions in the cation depleted region of the ionomer membrane has a negligible effect. The advantage of the model consists in its simplicity.