Evidence of counterion migration in ionic polymer actuators via investigation of electromechanical performance

• We investigated migration of counterions in ionomeric membrane of IEAP actuators.
• Counterions of Nafion ionomeric membrane are mobilized.
• Exchanging counterions with larger cations influences response of IEAP actuators.

Functional ionomeric polymer membranes are the backbone of a wide range of ionic devices; the mobility of ions through the ionomeric membrane is the principle of operation of these devices. Drift and diffusion of ions through ionomeric membranes strongly depend on the ionic properties of host membrane, as well as the physical and chemical properties of the ions. It is well-established that cations and anions provided via a dopant (e.g. electrolyte or ionic liquid) are mobilized under stimulation. However, in this study, we report that in addition to ions sourced by the dopant, counterions of the ionomeric membrane are also mobilized when stimulated. In particular, we have investigated the electromechanical response of ionic electroactive polymer actuators consisting of Nafion ionomeric membranes with different counterions and have demonstrated that those with cation counterions of larger Van der Waals volume exhibit stronger actuation due to motion of the larger cation counterions compared to actuators consisting of Nafion with counterion of smaller Van der Waals volumes.

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