Electro-mechanical Coupling Properties Of BaTiO₃/Nafion Ionic Polymer Metal Composite

Ionic Polymer Metal Composite（IPMC）is a new kind of electric active functional materials,which is comprised of a layer of ionic exchange membrane（e.g.,Nafion,Flemion,and Aciplex）plated with noble metal（e.g.,Pt,Ag）electrodes.It exhibits inherent advantages including low density,fast response,flexibility,structural simplicity and low excitation voltage.It can be widely applied in bio-mechanism,medical treatment,aeronautics and astronautics.However,the application and development of IPMC are limited by the performances of low driving force,complex response mechanism and nonlinear large deformation of IPMC.Aiming at these problems of IPMC,this thesis studied the fabrication technology and the basic performances of BaTiO₃/IPMC,the drive response analysis and electro-mechanical coupling modeling of IPMC.The fabrication process of IPMC was optimized.BaTiO₃/Nafion membranes were fabricated using the solution casting method,and then Pt-BaTiO₃/IPMCs were prepared using electrolss deposition.The microstructure and characteristics of BaTiO₃/IPMC samples with different mass ratio of BaTiO₃,were obtained by using scanning electron microscope.The basic properties of BaTiO₃/IPMCs including the dehydrating,mechanical and electrical properties were studied to measure the basic physical parameter.The results indicate that the water content of BaTiO₃/Nafion and BaTiO₃/IPMCs were less than the sample without BaTiO₃.Three kinds of testing methods including tension,bending,and post buckling methods were compared and used to measure the modulus of IPMC,which shows that the mechanical properties of BaTiO₃/Nafion and BaTiO₃/IPMCs were obveriously better than than the sample without BaTiO₃.The influence of the curvature of IPMC on surface electrode resistance,and the size influence on the capacitance and resistance of IPMC were obtained.Testing platforms were built to study the electroactive performances of BaTiO₃/IPMCs with different mass ratio of BaTiO₃ under excitation voltages.The results about the deformations and force output of the samples show that,the samples with BaTiO₃ nanoparticles exhibit the best overall property than the pure counterpart,and 3wt%BaTiO₃/IPMC sample was the best.The micro-scale displacement and strain distribution of IPMC actuator and its relation with the excitation voltages were revealed using DIC method and a digital microcope.Functional gradient model of BaTiO₃IPMC was proposed to predict the effective elastic modulus and the surface electrode resietance of IPMC.The IPMC is divided into three parts in our model,porous metal electrode,gradient polymer-metal composite electrode and membrane,based on the geometrically properties of the electroless plated metal electrode.The validity and accuracy of the model is justified with the experimental results of an IPMC sample.The results show that the errors between the predicted and experimental values of Young’s modulus and surface resistance of IPMC sample are+6.8%and-5.5%,respectively.Electromechanical modeling of IPMC was performed to predict the electroactive nonlinear deformation of IPMC.The large nonlinear deformation and the effect of curvature on surface electrode resistance of IPMC samples were investigated experimentally and theoretically.An irreversible thermodynamic model was used to predict the curvature of a unit part of IPMC actuator.A distributed RC electrical model was modified to establish an electromechanical model,and the empirical relation between curvature and deflection was used to establish an empirical elctromechanical model.And the two electromechanical models were then validated against the experimental results obtained from Pt-and Ag-IPMC actuators under various excitation voltages.The results show that the predicted and experimental values of deformation of IPMC samples agree within10%.The research on the fabrication method,elctroactive response and electromchanical model of IPMC in the thesis,could provide the necessary theoretical basis and research foundation for the follow-up study and application of IPMC.