Performance Characteristics of Electro–chemically Driven Polyacrylonitrile Fiber Bundle Actuators

Abstract

Polyacrylonitrile (PAN) gel is known for its large volume change when subjected to environmental stimuli. In particular, PAN fiber contracts when exposed to a low pH environment and expands when exposed to a high pH environment. Due to this phenomenon, PAN fibers can create effective actuation forces and displacements through muscle–like contractile behavior during the volume change. An alternative way to manage contraction/elongation is to generate a local pH gradient, which can be achieved through an electrochemical cell and is more convenient than using a pH changing solution. The main objective of this study is to investigate the chemo–mechanical (i.e., pH response) and electro–chemo–mechanical behavior of PAN bundle actuators in order to characterize the performance capability of PAN fiber gel as an effective soft actuator for new engineering applications. In order to do this, the shrinking and swelling properties of PAN gel fiber bundles under the influence of various stimuli, such as pH difference and electric field, are investigated and characterized, while a capability map has been suggested and compared with other conventional actuators. Pre–oxidized PAN fibers are annealed for 5 h at 220 C and then placed in a bundle configuration. Fibers of 30 strands, 150 mm in length, are bound as a soft actuator, with a ring gripper epoxied to each end of the bundle. After significant efforts were made to properly address the corrosive behavior of the electrode, performance characteristics of PAN actuators have been experimentally obtained and compared to other conventional actuator technologies. It was found that the actuation stress of PAN bundle actuators is in the range of a moving coil transducer, and the actuation strain is also better than a solenoid, as well as similar to natural muscle. The power, density, and frequency of a PAN actuator are within the range of other polymer gel actuators. The obtained maximum actuation stress and linear actuation strain are generally in the range of 2 10 3 –1 100 MPa and 20–100% for both chemically induced and electro–chemically induced PAN bundle actuators, respectively. Finally, suggestions for the practical application ranges of PAN actuation systems are given.