Peter Sommer-Larsen received his MS and PhD degree in physical chemistry from the University of Copenhagen, Denmark in 1985 and 1990 respectively. He is currently senior scientist in the Danish Polymer Centre at Risø National Laboratory, Denmark, where he is managing the ARTMUS research project on polymer based actuators.

Various classes of volume responsive polymers are reviewed. These may potentially act as actuators. A gel in equilibrium with its solvent will in general change volume in response to any change in the environment – temperature changes, changes in solvent composition and even electric fields. The volume of a gel may increase more than ten times upon swelling. Unfortunately, a very slow speed of response limits the potential of gels for actuators. Also, electric activation occurs in an indirect way - take an example – by creating a pH change in the solvent, which the gel responds to.

Nafion (tm) ion exchange membranes have been used to fabricate “ionomeric polymer metal composites” (IPMC) structures which act as actuators. A large number of researchers are working with these materials and actuators. They have been used to construct a soft micromanipulators and steer able catheters.

Conjugate polymers like polypyrrole and polyaniline form complexes with various anions that conducts electrons. These materials are directly electromechanically active: upon reduction and oxidation they change volume. A strip of polypyrrole can expand more than 10%, but although the oxidation/reduction process is fast, the structural changes are slow - the expansion takes minutes.

A composite of a polyelectrolyte gel with an interpenetrating conjugated polymer network was formed in order to speed up the response of gel contraction and making the material directly electric activated.

Composite structures of elastomers with compliant electrodes change form when a high electric potential difference is applied over the electrodes. Several thousands volts are needed, whereas the former actuators and materials all are activated by a few volts. On the other hand, such actuators have properties similar to pneumatics and in some respects they supersede the performance of electric motors.