Microelectro-mechanics of ionic polymeric gels as artificial muscles for robotic applications

Ionic polymeric gels are three-dimensional networks of cross-linked macromolecular polyelectrolytes that swell or shrink in aqueous solutions in addition of alkali or acids, respectively. Linear reversible dilation and contraction of the order of more than 1000 per cent are observed in a laboratory for polyacrylonitrile fibers. It is experimentally observed that swelling and shrinking of ionic gels can also be induced electrically. Thus, direct computer control of large expansions and contractions of ionic polymeric gels by means of a voltage gradient appears to be possible. A mechanism is presented for the reversible nonhomogeneous large deformations and in particular for bending of strips of ionic polymeric gels in the presence of an electric field. Exact expressions are given relating the deformation characteristics of the gel to the electric field strength or voltage gradient, gel dimensions and other physical parameters such as the resistance and the capacitance of the gel strip. It is concluded that direct voltage control of such nonhomogeneous large deformations in ionic polymeric gels is possible