The development of linear muscle‐like actuators remains a key objective in the field of electroactive polymers (EAPs). While ionic EAPs are promising technologies to develop biomimetic artificial muscles, their reliance on liquid electrolytes for operation typically restricts them to use in bending devices. Seldom have ionic linear actuators been demonstrated in air, and never in vacuum. Here both are demonstrated. A rational approach supported by a theoretical model is described to identify the general conditions allowing the design of ionic actuators with intrinsically linear deformations. The model highlights that linear deformation can occur by combining two electroactive electrodes with different mechanical and/or electromechanical properties. Where previous work on laminated actuators resulted in bending only, here it is shown that by combining one soft and one stiff electrode, or one highly expanding electrode, and the other minimally deforming electrode, 0.55% linear strain is achieved when activated with 2 V. Best combination of electrodes is selected based on electromechanical model predictions. Single actuator fibers are fabricated for experimental validation. Graded force up to 0.18 N has been achieved by bundling together five linear actuators. The resulting artificial muscles operate in open‐air, and also under high vacuum conditions, opening possibilities for space applications.

Trilayer bending actuators are charge driven devices that have the ability to function in air and provide large mechanical amplification. The electronic and mechanical properties of these actuators are known to be functions of their charge state making prediction of their responses more difficult when they operate over their full range of deformation. In this work, a combination of state space representation and a two-dimensional RC transmission line model are used to implement a nonlinear time variant model for conducting polymer-based trilayer actuators. Electrical conductivity and Young's modulus of electromechanically active PEDOT conducting polymer containing films as a function of applied voltage were measured and incorporated into the model. A 16% drop in Young's modulus and 24 times increase in conductivity are observed by oxidizing the PEDOT. A closed form formulation for radius of curvature of trilayer actuators considering asymmetric and location dependent Young's modulus and conductivity in the conducting polymer layers is derived and implemented in the model. The nonlinear model shows the capability to predict the radius of curvature as a function of time and position with reasonable consistency (within 4%). The formulation is useful for general trilayer configurations to calculate the radius of curvature as a function of time. The proposed electrochemical modeling approach may also be useful for modeling energy storage devices.

With the recent growing interest for soft actuation, many new types of ionic polymers working in air have been developed. Due to the interrelated mechanical, electrical, and chemical properties which greatly influence the characteristics of such actuators, their behavior is complex and difficult to understand, predict and optimize. In light of this challenge, an original linear multiphysics finite difference bond graph model was derived to characterize this ionic actuation. This finite difference scheme was divided into two coupled subparts, each related to a specific physical, electrochemical or mechanical domain, and then converted into a bond graph model as this language is particularly suited for systems from multiple energy domains. Simulations were then conducted and a good agreement with the experimental results was obtained. Furthermore, an analysis of the power efficiency of such actuators as a function of space and time was proposed and allowed to evaluate their performance.

Metals and glass are excellent for containing electrolytes and liquids in general, but their rigid mechanics limits their application for mechanically active ionic actuators or flexible/ stretchable electrochemical devices such as batteries and supercapacitors. In this study, we evaluate the performance of spray-coated poly (styrene-block-isobutylene-block-styrene) (SIBS) as a stretchable encapsulant, which suggests that it offers a better combination of compliance and impermeability than any other barrier. We examined the drying time of 360-µm thick encapsulated tri-layer conducting polymer (CP) actuators, comprised of poly(3,4-Ethylenedioxythiophene) (PEDOT) as the CP electrode and an interpenetrated polymer network of polyethylene oxide (PEO) and nitrile butadiene rubber (NBR) as the separator layer, which operates with a 1 M solution of Lithium bis(trifluoromethanesulfonyl)imide (Li + TFSI − ) in propylene carbonate (PC). A 100-µm thick SIBS encapsulation layer is anticipated to help these devices to retain 80% of stored PC for more than 1000 times longer compared to when there is no encapsulation (from less than 0.5 days to over 1.5 years). This low permeability combined with the low Young's modulus of the SIBS film, its biocompatibility, biostability, and FDA approval, as well as ease of fabrication, make this thermoplastic elastomer a promising candidate as an encapsulant for flexible ionic devices such as flexible batteries and supercapacitors, ionic-electrode capacitive sensors, and ionically electroactive actuators. This paves the way for using these devices in implantable and in vivo applications. ]. Moreover, in some applications where the device is required to work in a liquid environment other than its electrolytes, such as in water or blood, if the device is not well protected against its environment, ions and solvent will leave the device over time and will be substituted by the environment molecules [1,2]. The encapsulating layer can also serve as a protection against the escape of hazardous electrolytes for applications where direct user interactions are involved, such as biomedical devices [12,13] and tactile interfaces [14].Among different types of ionic devices, encapsulation of ionic bending actuators such as tri-layer conducting polymers [1,2], Bucky gels [15], and ionic polymer metal composites (IPMCs) [3,4] is the most challenging since they are typically soft, and the mechanical properties of the encapsulating layer can significantly alter their performance. An encapsulating material for these actuators should be (1) a good barrier that limits the exchange of molecules with the environment, (2) flexible enough to not prevent the bending, (3) able to be deposited under conditions compatible with the materials that the device is made of, and (4) stable over the lifetime of the device in its operation and storage environments. The effectiveness of the encapsulating layer for ionic bending actuators have been mostly evaluated by measuring the change in the device's displacement during cycli...

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