Abstract
Controllable linear actuation of polypyrrole (PPy) is the envisaged goal where only one ion dominates direction (here anions) in reversible redox cycles. PPy with polyethylene oxide (PEO) doped with dodecylbenzenesulfonate forms PPy-PEO/DBS films (PPy-PEO), which are applied in propylene carbonate (PC) solvent with electrolytes such as 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate (EDMICF3SO3), sodium perchlorate (NaClO4) and tetrabutylammonium hexafluorophosphate (TBAPF6) and compared in their linear actuation properties with pristine PPy/DBS samples. PPy-PEO showed for all applied electrolytes that only expansion at oxidation appeared in cyclic voltammetric studies, while pristine PPy/DBS had mixed-ion actuation in all electrolytes. The electrolyte TBAPF6-PC revealed for PPy-PEO best results with 18% strain (PPy/DBS had 8.5% strain), 2 times better strain rates, 1.8 times higher electronic conductivity, 1.4 times higher charge densities and 1.5 times higher diffusion coefficients in comparison to PPy/DBS. Long-term measurements up to 1000 cycles at 0.1 Hz revealed strain over 4% for PPy-PEO linear actuators, showing that combination of PPy/DBS with PEO gives excellent material for artificial muscle-like applications envisaged for smart textiles and soft robotics. FTIR and Raman spectroscopy confirmed PEO content in PPy. Electrochemical impedance spectroscopy (EIS) of PPy samples revealed 1.3 times higher ion conductivity of PPy-PEO films in PC solvent. Scanning electron microscopy (SEM) was used to investigate morphologies of PPy samples, and EDX spectroscopy was conducted to determine ion contents of oxidized/reduced films.
Highlights
Conducting polymer (CP) actuators have been in research for nearly over 30 years with the aim at first to understand how actuation can be controlled and applied
We want to demonstrate that the mixed-ion activity can be reduced in PPy-polyethylene oxide (PEO) linear actuators in comparison to PPy/DBS types, leading to high strain adaptability as an “artificial muscle” candidate
Raman peaks of PPy [41,42,43] (Figure 2b) can be found at 1571 cm−1 (PPy-PEO) with a shift to 1579 cm−1 for PPy/DBS that represents the C=C backbone stretching. The shift in such peaks represents the conductivity of the samples, and shifts to lower frequency shown from previous research [41] refer to a higher oxidation state and an increase in conductivity (Table 1) of PPy-PEO/DBS films (PPy-PEO)
Summary
Conducting polymer (CP) actuators have been in research for nearly over 30 years with the aim at first to understand how actuation can be controlled and applied. The other case of cation-driven actuation is immobile anions such as DBS− incorporated during electropolymerization forming PPy/DBS films leading to expansion at reduction, named cation-driven actuation. Those specified types do not comply if different electrolytes [7] or solvents [8] are applied, leading in most cases to the unfavorable mixed-ion actuation or changes in actuation directions (in the special case of PPy/DBS becoming anion-driven in propylene carbonate electrolyte [9]). EDX spectroscopy of PPy-PEO and PPy/DBS films after actuation were analyzed to evaluate which elements can be found in oxidized and reduced samples
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