Exchanged Cations and Water during Reactions in Polypyrrole Macroions from Artificial Muscles

Abstract

The movement of the bilayer (polypyrrole-dodecylbenzenesulfonate/tape) during artificial muscle bending under flow of current square waves was studied in aqueous solutions of chloride salts. During current flow, polypyrrole redox reactions result in variations in the volumes of the films and macroscopic bending: swelling by reduction with expulsion of cations and shrinking by oxidation with the insertion of cations. The described angles follow a linear function, different in each of the studied salts, of the consumed charge: they are faradaic polymeric muscles. The linearity indicates that cations are the only exchanged ions in the studied potential range. By flow of the same specific charge in every electrolyte, different angles were described by the muscle. The charge and the angle allow the number and volume of both the exchanged cations and the water molecules (related to a reference) between the film to be determined, in addition to the electrolyte per unit of charge during the driving reaction. The attained apparent solvation numbers for the exchanged cations were: 0.8, 0.7, 0.6, 0.5, 0.5, 0.4, 0.25, and 0.0 for Na(+), Mg(2+), La(3+), Li(+), Ca(2+), K(+), Rb(+), and Cs(+), respectively.

Bending Monolayer Artificial Muscle

“…The coulo‐dynamic specific efficiency of the system (polypyrrole‐DBS, LiClO 4 , water) is the slope from Figure b: 0.53 mC mg −1 (°) −1 . This is the highest specific efficiency (Table ) among bending artificial muscles exchanging anions (positive slope) or cations (negative slope) described in the literature ,,…”

“…This is the highest specific efficiency (Table 1) among bending artificial muscles exchanging anions (positive slope) or cations (negative slope) described in the literature. [36,44,45] The irreversible charge consumed at the higher cathodic potential range (Figure 3b) does not give any bending movement of the muscle, as observed in Figure 4b, from point 1 to point 2. In addition it produces a small creeping chemical effect: the muscle does not recover at the end of the cycle 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 (point 10) the departure position at the beginning of the potential cycle (point 1).…”

“…The polypyrrole coating the steel borders was scraped. Two independent films were peeled of, one by electrode side, from the working electrode ,,. The films were then submerged in de‐ionized water for 48 hours to remove DBSA adsorbed on the polypyrrole surface.…”

“…The film oxidation/reduction drives the expulsion/entrance of cations and solvent from/towards, respectively, the solution (reaction 1) for charge and osmotic balance. [36][37][38][39][40][41] The parallel reversible bending movements reveal the great electroactivity (large shrinking/swelling variations) of the film surface in contact with the electrolyte during the film electrogeneration (fresh films interface). The film surface touching the polymermetal interface during electrogeneration (old film interface, Figure 1) presents a minor electroactivity.…”

“…Two independent films were peeled of, one by electrode side, from the working electrode. [36,42,55] The films were then submerged in de-ionized water for 48 hours to remove DBSA adsorbed on the polypyrrole surface. Finally the pPy-DBS films were air-dried at room temperature.…”