<title>Microelectromechanics of ionic polymeric gels as synthetic robotic muscles</title>

Abstract

An ionic polymeric gel is defined as a 3-D charged network of a cross-linked macromolecular polyelectrolyte capable of collapsing or swelling in an acidic or alkaline environment, respectively, purely due to pH changes. Fixed electrical charges reside at all cross-links in such macromolecular networks in the presence of wandering mobile charges that tend to change their spatial distribution within the gel network. In the presence of an electric field, the mobile ions redistribute themselves in the gel network and thus cause the network to deform accordingly. A microelectro-mechanical model is presented that takes into account such internal electric charge redistribution of fixed and mobile ions due to the presence of an electric field. 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 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. It is concluded that direct voltage control of such nonhomogeneous large deformations in ionic polymeric gels is possible.