Abstract
Linear actuators based on polypyrrole (PPy) are envisaged to have only one ion that triggers the actuation direction, either at oxidation (anion-driven) or at reduction (cation-driven). PPy doped with dodecylbenzenesulfonate (PPy/DBS) is the most common applied conducting polymer having cation-driven actuation in aqueous solvent and mainly anion-driven actuation in an organic electrolyte. It is somehow desired to have an actuator that is independent of the applied solvent in the same actuation direction. In this research we made PPy/DBS with the addition of phosphorus tungsten acid, forming PPyPT films, as well with included carbide derived carbon (CDC) resulting in PPyCDC films. The solvent in electropolymerization was changed from an aqueous ethylene glycol mixture to pure EG forming PPyPT-EG and PPyCDC-EG composites. Our goal in this study was to investigate the linear actuation properties of PPy composites applying sodium perchlorate in aqueous (NaClO4-aq) and propylene carbonate (NaClO4-PC) electrolytes. Cyclic voltammetry and square potential steps in combination with electro-chemo-mechanical-deformation (ECMD) measurements of PPy composite films were performed. The PPyPT and PPyCDC had mixed ion-actuation in NaClO4-PC while in NaClO4-aq expansion at reduction (cation-driven) was observed. Those novel PPy composites electropolymerized in EG solvent showed independently which solvent applied mainly expansion at reduction (cation-driven actuator). Chronopotentiometric measurements were performed on all composites, revealing excellent specific capacitance up to 190 F g−1 for PPyCDC-EG (best capacitance retention of 90 % after 1000 cycles) and 130 F g−1 for PPyPT-EG in aqueous electrolyte. The films were characterized by scanning electron microscopy (SEM), Raman, Fourier-transform infrared (FTIR) and energy dispersive X-ray spectroscopy (EDX).
Highlights
IntroductionPPy doped with DBS− is one of the best studied types of conducting polymer materials, found in various formations in micro-fabrication [1] such as micro-robotic devices [2,3]
The inclusion of carbide-derived carbon (CDC) in electropolymerization with the addition of PTA shown for PPyCDC (Figure 1d) had a quite rough surface morphology with CDC particles on the surface being more apparent in the cross section image (Figure 1d inset)
Electropolymerization at low temperature needs anti-freezing agents, for which in general EG is applied mixed with aqueous solvent forming PPy doped with DBS− with the addition of PTA and CDC composite films such as PPyPT and PPyCDC
Summary
PPy doped with DBS− is one of the best studied types of conducting polymer materials, found in various formations in micro-fabrication [1] such as micro-robotic devices [2,3]. Biomedical applications [4], biochips to trigger cell growth over actuation [5] and, recently, smart textile fabrications [6]. Addition of charged molecules such as polyoxometalates (Keggin type [7], phosphotungstic acid (PTA, PW12 O40 3− )) forming PPyDBS-PT composites revealed strain in aqueous electrolyte in range of 5.2% [8]. Additional incorporation of meso-porous carbide-derived carbon (CDC) particles forming PPyDBS-PT-CDC (PPyCDC). Linear films [9] had strain in the range of 12% while PPyDBS linear actuators strain values varied at 4–6% strain depending on the choice of electrolyte applied [10].
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