Progress of experimental characterization and micromechanistic modeling of actuation of ionic polymer-metal composites

Ionic polymer-metal composites (IPMCs) consist of a polyelectrolyte membrane (usually, Nafion or Flemion) plated on both faces by a noble metal, and is neutralized with certain counterions that balance the electrical charge of the anions covalently fixed to the backbone membrane. In the hydrated state, a cantilevered strip of this composite performs bending vibration when subjected to an AC potential across its faces, and it produces millivolt potential when suddenly bent. Thus the composite is a soft actuator and sensor. Its coupled electrical-chemical-mechanical response depends on the chemical composition and structure of the backbone ionic polymer; the morphology of the metal electrodes; the nature of the cations; and the level of hydration. A systematic experimental evaluation of the mechanical response of both metal-plated and bare Nafion in various cation forms and various water saturation levels has been performed at UCSD. By examining the measured stiffness of the Nafion-based composites and the corresponding bare Nafion, under a variety of conditions, I have develop relations between internal forces and the resulting stiffness and deformation of this class of IPMCs. Based on these and through a comparative study of the effects of various cations on the material's stiffness and response, I have sought to identify potential micro-mechanisms responsible for the observed electro-mechanical behavior of these materials, model them, and compare the model results with experimental data. A summary of some of these developments is given in the present work.