Artificial muscles driven by the cooperative actuation of electrochemical molecular machines. Persistent discrepancies and challenges

Figures & data

Figure 1. Ideal multielectronic electrochemical molecular machine. The neutral chain presents a coil like structure in an electrolyte. By extraction of consecutive electrons consecutive planar polaronic (conjugated radical cations) structures are generated promoting conformational movements of the chain and a stick like structure. Anions are attracted from the solution for charge balance forming a linear electrical double layer along the chain. Reproduced with permission from ref [13]., 1999, Kluwer.

Figure 2. The polymer oxidation (reaction 1 forwards) promotes the cooperative actuation of the molecular machines (the polymer chains) constituting the polymer film. Free volume is generated to incorporate balancing counterions and solvent required for osmotic balance. The material becomes a dense gel constituted by molecular machines, ions and solvent, which swells during its oxidation. During reduction reverse processes occur and the film shrinks. Reconstructed with permission from ref [13]. 1999, Kluwer.

Figure 3. A PPy/tape bilayer muscle was submitted to consecutive potential sweeps from 1.00 V to −2.50 V, at 5 mVs⁻¹ in 0.1 M LiClO₄ aqueous solution. (a) Stationary voltammetric response after three consecutive potential cycles. (b) Parallel evolution of the consumed charge, coulovoltammetric response (black line), and parallel evolution of the angle described by the muscle, voltammo-dynamics response (dotted red line). (c) Amplitude of the described angle for different consumed charges: coulo-dynamic response. Pictures 1–6 show the bending position of the muscle for the same points, 1 to 6, on figures 2a, 2b and 2c. The last picture overlaps pictures 3, 4 and 5. Reproduced with permission from Ref [109]. Elsevier.

Figure 4. (a) Closed coulovoltammetric response from a polypyrrole film coating a Pt electrode in 0.1 M NaCl aqueous solution to a potential sweep at 50 mV s⁻¹ from – 0.5 to 0.3 V; and open coulovoltammetric response from – 1.35 to 0.3 V.; Q_redox is the film reduction/oxidation reversible charge and Q_i, the irreversible cathodic charge consumed by parallel irreversible redution reactions. (b1) The open loop curve shows the charge involved in a new irreversible oxidation process (Q_i) plus the film redox charge; (b2) The closed loop shows the film reversible redox film charge, Q_redox. Reproduced with permission from Ref [19]., Wiley.

T.F. Otero, Conducting polymers, electrochemistry, and biomimicking processes, in Modern Aspects of Electrochemistry, R.E. White, J.O. Bockris, and B.E. Conway, eds., Springer US, New York, 1999, pp. 307–434. Available at http://link.springer.com/chapter/10.1007/0-306-46917-0_3. accessed January 9, 2013).

 Google Scholar

T.F. Otero and J.G. Martinez, Ionic exchanges, structural movements and driven reactions in conducting polymers from bending artificial muscles, Sens. Actuators B Chem. 199 (2014), pp. 27–30. doi:10.1016/j.snb.2014.03.053

 Web of Science ®Google Scholar

T.F. Otero, M. Alfaro, V. Martinez, M.A. Perez, and J.G. Martinez, Biomimetic structural electrochemistry from conducting polymers: Processes, charges, and energies. coulovoltammetric results from films on metals revisited, Adv Funct Mater. 23 (2013), pp. 3929–3940. doi:10.1002/adfm.201203502

 Web of Science ®Google Scholar