Ion transport in ionomeric polymers for ionic electroactive polymer devices

Abstract

<p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>In a collaborative effort, we have also developed a nonlinear dynamic model of IEAP actuators using rigid finite element method.</p>