Physical interpretation of deformation evolvement with water content of ionic polymer-metal composite actuator

Water-based Nafion ionic polymer metal composites (IPMC) exhibit complex deformation properties. In this paper, three eigen stresses, osmotic pressure, total electrostatic stress, and capillary pressure, are investigated with water concentration at various cation concentration levels and compared with the reference hydrostatic pressure, in order to give a physical interpretation on the deformation evolvement with water content. By numerical analysis it is found that under various saturation conditions, the steady-state of the relaxation deformation is dominated by the magnitudes of the osmotic pressure and the total electrostatic stress. When the former is less than the later, IPMC actuator will show a positive steady-state deformation such as the case of Pd-IPMC (water content 20 w.t.%), and vice versa for the case of Au-IPMC (water content 18 w.t.%). With the water content initially decreasing (no more than 4 w.t.%), the relaxation deformation decreases. It is due to the increase of the osmotic pressure and the decrease of the total electrostatic stress. With further decreasing, the relaxation deformation disappears. It is due to the decrease of the cation mobility. And the amplitude of the anode deformation is mainly decided by the effective electrical constant. (C) 2013 AIP Publishing LLC.