Influence of conductive network composite thickness and structure on performance of ionic polymer-metal composite transducer

The important role of the nanostructure of conductive network composite (CNC) layers on the performance of ionic polymer-metal composite (IPMC) transducer has been discussed detailedly. IPMC transducers exhibit both electromechanical and mechanoelectrical behaviors. When subjected to an external electric field, electromechanical behavior of IPMC transducers causes an actuation response which can be reversed by alternation of the polarity of the applied field. The same structure, when subjected to an external mechanical force, generates an electrical signal which can be picked up by ordinary electronic. Mechanoelectrical behavior of IPMCs is utilized in stress sensors and structural health monitoring devices. We have employed the layer by layer (LbL) self-assembly technique to fabricate CNC layers based on spherical gold nanoparticles (AuNPs) and poly(allylamine hydrochloride) (PAH) polycation with a controllable thickness in nano and micro ranges; which, when compared with IPMC transducer without CNC layers on both sides of ionomeric membrane, show an improvement in the actuation and sensing performances significantly. Moreover, the thickness and conformation of CNC nanostructure can also be adjusted by the addition of small salt molecules. The presence of salt ions can affect the conformation of polymer chains and their molecular shape since it screens the repulsive force among the same charges on the repeat units of polyelectrolyte. As a result, the polymer chains become more coiling when dissolved in an environment with high ionic strength. At the same time, while part of the charges have been screened, larger amount of polymer chains or nanoparticles are required to reverse the surface charge led by the previous layer. The presence of salt ions in CNC can also prohibit the aggregation of AuNPs and promote a more homogeneous distribution of the nanoparticles. In this case, both the thickness and conformation of CNC have been changed; which, as indicated by experimental results, has a positive influence on the actuation and sensing performance of IPMC devices

Ion transport in ionomeric polymers for ionic electroactive polymer devices

Recently, electroactive polymers (EAPs) have received immense attention and interest from the materials community because of their promising properties such as light weight, high elastic energy density and easy processing, which provide them the applicability in wide areas including solar cells, super capacitors, actuators and sensors. Among wide variety of electroactive polymers, ionic electroactive polymer (IEAP) has been proven more practical for both actuator and sensor applications. This dissertation discusses the the limiting factors in IEAP actuators and sensors. Three important components, ionomeric polymer membrane, conductive network composites (CNCs) and electrolytes, all have significant determination on the performance of IEAP actuators and sensors. Thorough investigation are conducted by both experimental and theoretical methods, and the findings are presented in this dissertation. We first investigated how the morphology of CNC thin-film influences the mechanoelectrical performance of IEAP sensors. IEAP sensor, in most cases, is also referred to as ionic polymer-metal composite (IPMC) sensor. A novel approach, layer-by-layer (LbL) ionic self-assembly technique is utilized to fabricate the porous and conductive CNC nanocomposites based on polymers and metal nanoparticles. The electrochemical, morphological characteristics, and the corresponding mechanoelectrical performance of this IEAP sensor were explored as a function of the CNC morphology. Meanwhile, the influence of ionic liquids (ILs) concentration on the electromechanical response of IEAP actuators has been investigated. It was observed that an optimum concentration of ions where the electromechanical response is maximized is achieved by adjusting the uptake of IL in the ionomeric membrane; this optimum concentration, however, is not the highest ion concentration. Functional ionomeric polymer membrane is the backbone of a wide range of ionic devices due to its permeability to ions, which is the principle of these devices. Ions are sourced by either aqueous electrolytes or ILs. ILs are preferred as their near zero vapor pressure allows longer shelf life, operation in air, and higher operation voltages. We report that in addition to ions sourced by the dopant (e.g. electrolytes or ILs), counterions of the ionomeric membrane contained in the IEAP actuator are also mobilized and contribute to the final electromechanical response. Many approaches to fabricate CNC thin-film structures have been proposed and enabled an intrinsic way to control the performance of IEAP actuators. We have demonstrated that manipulation of ionic mobility through means of structural design can realize intrinsic limb-like motion in IEAP actuators. By incorporating conjugated polymers in desired patterns as CNC thin-films, we have developed unique IEAP actuators which are capable of exhibiting limb-like angular deformation. In a collaborative effort, we have also developed a nonlinear dynamic model of IEAP actuators using rigid finite element method.</p

Influence of conductive network composite thickness and structure on performance of ionic polymer-metal composite transducer

The important role of the nanostructure of conductive network composite (CNC) layers on the performance of ionic polymer-metal composite (IPMC) transducer has been discussed detailedly. IPMC transducers exhibit both electromechanical and mechanoelectrical behaviors. When subjected to an external electric field, electromechanical behavior of IPMC transducers causes an actuation response which can be reversed by alternation of the polarity of the applied field. The same structure, when subjected to an external mechanical force, generates an electrical signal which can be picked up by ordinary electronic. Mechanoelectrical behavior of IPMCs is utilized in stress sensors and structural health monitoring devices. We have employed the layer by layer (LbL) self-assembly technique to fabricate CNC layers based on spherical gold nanoparticles (AuNPs) and poly(allylamine hydrochloride) (PAH) polycation with a controllable thickness in nano and micro ranges; which, when compared with IPMC transducer without CNC layers on both sides of ionomeric membrane, show an improvement in the actuation and sensing performances significantly. Moreover, the thickness and conformation of CNC nanostructure can also be adjusted by the addition of small salt molecules. The presence of salt ions can affect the conformation of polymer chains and their molecular shape since it screens the repulsive force among the same charges on the repeat units of polyelectrolyte. As a result, the polymer chains become more coiling when dissolved in an environment with high ionic strength. At the same time, while part of the charges have been screened, larger amount of polymer chains or nanoparticles are required to reverse the surface charge led by the previous layer. The presence of salt ions in CNC can also prohibit the aggregation of AuNPs and promote a more homogeneous distribution of the nanoparticles. In this case, both the thickness and conformation of CNC have been changed; which, as indicated by experimental results, has a positive influence on the actuation and sensing performance of IPMC devices.</p

Influence of Temperature on the Electromechanical Properties of Ionic Liquid-Doped Ionic Polymer-Metal Composite Actuators

Ionic polymer-metal composite (IPMC) actuators have considerable potential for a wide range of applications. Although IPMC actuators are widely studied for their electromechanical properties, most studies have been conducted at the ambient conditions. The electromechanical performance of IPMC actuators at higher temperature is still far from understood. In this study, the effect of temperature on the electromechanical behavior (the rate of deformation and curvature) and electrochemical behavior (current flow) of ionic liquid doped IPMC actuators are examined and reported. Both electromechanical and electrochemical studies were conducted in air at temperatures ranging from 25 °C to 90 °C. Electromechanically, the actuators showed lower cationic curvature with increasing temperature up to 70 °C and a slower rate of deformation with increasing temperature up to 50 °C. A faster rate of deformation was recorded at temperatures higher than 50 °C, with a maximum rate at 60 °C. The anionic response showed a lower rate of deformation and a higher anionic curvature with increasing temperatures up to 50 °C with an abrupt increase in the rate of deformation and decrease of curvature at 60 °C. In both cationic and anionic responses, actuators started to lose functionality and show unpredictable performance for temperatures greater than 60 °C, with considerable fluctuations at 70 °C. Electrochemically, the current flow across the actuators was increased gradually with increasing temperature up to 80 °C during the charging and discharging cycles. A sudden increase in current flow was recorded at 90 °C indicating a shorted circuit and actuator failure

Soft Ionic Electroactive Polymer Actuators with Tunable Non-Linear Angular Deformation

The most rational approach to fabricate soft robotics is the implementation of soft actuators. Conventional soft electromechanical actuators exhibit linear or circular deformation, based on their design. This study presents the use of conjugated polymers, Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) to locally vary ion permeability of the ionic electroactive polymer actuators and manipulate ion motion through means of structural design to realize intrinsic angular deformation. Such angular deformations are closer to biomimetic systems and have potential applications in bio-robotics. Electrochemical studies reveal that the mechanism of actuation is mainly associated with the charging of electric double layer (EDL) capacitors by ion accumulation and the PEDOT:PSS layer’s expansion by ion interchange and penetration. Dependence of actuator deformation on structural design is studied experimentally and conclusions are verified by analytical and finite element method modeling. The results suggest that the ion-material interactions are considerably dominated by the design of the drop-cast PEDOT:PSS on Nafion

Nonlinear dynamic modeling of ionic polymer conductive network composite actuators using rigid finite element method

Ionic polymer conductive network composite (IPCNC) actuators are a class of electroactive polymer composites that exhibit some interesting electromechanical characteristics such as low voltage actuation, large displacements, and benefit from low density and elastic modulus. Thus, these emerging materials have potential applications in biomimetic and biomedical devices. Whereas significant efforts have been directed toward the development of IPMC actuators, the establishment of a proper mathematical model that could effectively predict the actuators\u27 dynamic behavior is still a key challenge. This paper presents development of an effective modeling strategy for dynamic analysis of IPCNC actuators undergoing large bending deformations. The proposed model is composed of two parts, namely electrical and mechanical dynamic models. The electrical model describes the actuator as a resistive-capacitive (RC) transmission line, whereas the mechanical model describes the actuator as a system of rigid links connected by spring-damping elements. The proposed modeling approach is validated by experimental data, and the results are discussed. &copy; 2014 Elsevier B.V. All rights reserved