Mass transfer induced hydraulic actuation in ionic polymer-metal composites

Discussed is the phenomenon of mass transfer-induced hydraulic actuation in ionic polymer-metal composites (IPMCs) strips with chemically plated surface electrodes. A new category of actuators as mass transfer induced hydraulic actuators (MTIHAs) is thus defined. Such mass transport of ions and water is across the thickness of the strip and ends up near the permeable metal electrodes. The imposition of an electric field causes the mobile hydrated cations that are conjugated to the polymeric network anions to undergo electrophoretic dynamic migration that can result in local deformation of the material. Such an electrophoretic behavior of the hydrated cations in IPMC causes the water to flow across the strip and partially leak out of the cathode side of the permeable electroded boundary. These leakages are undesirable because they lower the actuation performance. The IPMC is a good example of such MTIHAs. The advantage of MTIHAs is their potential to generate substantially high force densities if the leakage can be minimized or eliminated. Based upon this MTIHA concept, a certain manufacturing technique was developed to minimize the leakage and increase the force density of the conventional IPMCs by almost a factor of two (100% improvement in force). This phenomenon and the associated experimental results are presented in this paper.