Creeping and structural effects in Faradaic artificial muscles

Abstract

Reliable polymeric motors are required for the construction of rising accurate robots for surgeon assistance. Artificial muscles based on the electrochemistry of conducting polymers fulfil most of the required characteristics, except the presence of creeping effects during actuation. To avoid it, or to control it, a deeper knowledge of its physicochemical origin is required. With this aim here bending bilayer tape/PPy-DBSH (Polypyrrole-dodecylbenzylsulphonic acid) full polymeric artificial muscles were cycled between −2.5 and 1 V in aqueous solutions with parallel video recording of the described angular movement. Coulo-voltammetric (charge-potential, QE), dynamo-voltammetric (angle-potential, αE), and coulo-dynamic (charge-angle, Qα) muscular responses corroborate that 10 % of the charge is consumed by irreversible reactions overlapping the polymer reduction at the most cathodic potentials. In parallel, the range of the bending angular movement (145°) shifts by 15°per cycle (creeping effect) pointing to the irreversible charge as possible origin of the irreversible swelling of the PPy-DBS film. Different slopes in the closed loop part of the QE identify the different reaction driven structural processes in the film: oxidation-shrinking, oxidation-compaction, reduction-relaxation, reduction-swelling, and reduction-vesicle's formation. Despite the irreversible charge fraction, the muscle motor keeps a Faradaic behaviour: described angles are linear functions of the consumed charge in the full potential range.

Bending Monolayer Artificial Muscle

“…By combining Figure a and Figure b the coulo‐dynamic (charge‐angle) characterization (Figure b) of the muscle during each voltammetric cycle is attained. A linear, in average, control of the muscle angular position (α) with the consumed charge (Q) is obtained corroborating the Faradaic nature (driven by reaction 1) of those polymeric motors, as described by Equation :,,, …”

A Potentiostatic/Galvanostatic Study and Theoretical Description of Polypyrrole Film Electrodes: A Model of the Intracellular Matrix of Ectothermic Muscle Cells

“…Thus, reaction 1 drives reversible conformational (or allosteric) movements of each reactant polymeric chain originating a multistep electrochemical molecular machine ,. The cooperative actuation of those molecular machines in a reacting polypyrrole film electrode gives macroscopic structural volumetric (swelling, shrinking, conformational compaction and conformational relaxation) changes, required to lodge, expel or trap balancing counterions and solvent . By cooperative actuation of the constitutive polymeric motors a free volume is generated in the polymer film during oxidation, which swells to lodge those counterions and solvent coming from the solution and required for the reaction completion.…”

“…[30,31] The cooperative actuation of those molecular machines in a reacting polypyrrole film electrode gives macroscopic structural volumetric (swelling, shrinking, conformational compaction and conformational relaxation) changes, required to lodge, expel or trap balancing counterions and solvent. [32][33][34] By cooperative actuation of the constitutive polymeric motors a free volume is generated in the polymer film during oxidation, which swells to lodge those counterions and solvent coming from the solution and required for the reaction completion. By cooperative actuation the film shrinks during reduction with expulsion of counterions and solvent towards the solution.…”

Construction and coulodynamic characterization of PPy-DBS-MWCNT/tape bilayer artificial muscles

“…[1][2][3][4][5][6] During the oxidation/reduction of the electroactive material counterions and solvent molecules are exchanged with the electrolyte to keep the charge balance inside the film and the osmotic balance between the material and the electrolyte. [10][11][12][13][14][15] They are electro-chemo-mechanical transducers. Bending bilayer artificial muscles transduce minor reaction-driven ionic exchanges into large angular (> 30°) displacements.…”