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Simultaneous actuation and sensing properties of a triple layer actuator interchanging cations are presented for the first time. Thick polypyrrole (pPy)/dodecylbenzenesulfonate (DBS) films (36 mm) were electrogenerated on stainless steel electrodes. Sensing characteristics of pPy-DBS/tape/pPy-DBS triple layer artificial muscle were studied as a function of electrolyte concentration, temperature and driving current using lithium perchlorate (LiClO 4 ) aqueous solution as electrolyte. The chronopotentiometric responses were studied by applying consecutive square waves of currents to produce angular movements of AE45 by the free end of the triple layer. The evolution of the muscle potential (anode film versus cathode film) during current flow is a function of the studied chemical and physical variables. The electrical energy consumed to describe a constant angle is a linear function of the working temperature or of the driving electrical current, and a double logarithmic function of the electrolyte concentration. Those are the sensing functions. The cation exchanging bending triple layer actuator senses the working conditions. Similar sensing functions were described in the literature for devices interchanging anions. Irrespective of the reaction mechanism, a single electrochemo-mechanical device comprised of two reactive polymer electrodes (oxidation film and reduction film) works simultaneously as both sensor and actuator (self-sensing actuators). These are the general sensing properties of dense and biomimetic reactive gels of conducting polymers. Thus, any reactive device based on the same type of materials and reactions (batteries, smart windows, actuators, electron-ion transducers) is expected to sense surrounding conditions, as biological organs do.

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Artificial muscle fiber mimicking myofibril is fabricated using electrospun nanofibers of high strength polyurethane followed by controlled in situ chemical polymerization with aniline. The resulting polyurethane(PU)/polyaniline(PANi) hybrid nanofibrous bundle consisting individual nanofibers of about 900 nm diameter responds to an electrical stimuli producing a linear actuation strain as high as 1.65% at an applied stress of 1.03 MPa in 1 M methane sulfonic acid (MSA), the highest strain produced in the nanofibers templated PANi. The hybrid nanofibrous bundle shows an electrical conductivity of about 0.5 S/cm and the electroactivity is imparted by PANi. The biomimetic artificial nanofibrous bundle shows work per cycle (W.C.) efficiency of above 75% for the electrochemical actuation even beyond 100 cycles. The PU/PANi hybrid nanofibrous bundle could be stably actuated without significant creep up to an applied load of 11 mN (2.263 Mpa) beyond which significant creep behavior appears.

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Flexible, controllable, and stable electrochemical supercapacitors serving as actuators at low operating voltage combining the advantages of the high power of the dielectric capacitors and the high specific energy of rechargeable batteries are important in artificial muscle technology, hybrid electric vehicles, and in short-term power sources for mobile electronic devices [ Baughman , Science , 300 , 268 (2003) ; Winter and Brodd , Chem. Rev. (Washington, D.C.) , 104 , 4245 (2004) ; Ebron , et al. , Science , 311 , 1580 (2006) ]. High capacitance, a surprising 99% inner charge contribution and actuation in the hydrogel-assisted actuatable electrochemical supercapacitor (HAES) microfiber fabricated through wet spinning of a chitosan solution, followed by the in situ chemical polymerization of aniline was made possible through the perfect utilization of the large surface area provided by the nanostructured polyaniline grown inside as well as on the surface of the fiber. The HAES electrodes with an actuation strain of 0.33% showed 703F∕g specific capacitance in 1M methane sulfonic acid, and more than 3000cycles durability. The change in impedance as well as capacitance was achieved by the controlled strain as a function of applied stress, which can establish a direct relationship between the actuation strain and specific capacitance of electrochemical supercapacitors.

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