Electrolyte and solvent effects in PPy/DBS linear actuators

• PPy/DBS actuation is established in organic and ‘ueous electrolytes.
• Changing of actuation direction was achieved during cycling.
• PPy/DBS can be modified from cation-driven to anion-driven actuation.

An important question with conducting polymer linear actuators concerns the processes that occur once the electrolyte is changed. To address this question, a series of electro-chemo-mechanical deformation (ECMD) measurements on electrochemically prepared free-standing films of polypyrrole doped with dodecylbenzenesulfonate (DBS) were investigated under isometric (constant force) conditions in an organic solvent- and in aqueous based-electrolytes during cyclic voltammetric and square wave potential step experiments. The same film was actuated first in propylene carbonate electrolyte (0.1 M TBACF3SO3), where cation-driven actuation (12% strain) was observed. The film was then exposed to an aqueous electrolyte (0.2 M TMACl) where the actuation changed to anion-driven (7% strain). The same film was then returned to the propylene carbonate electrolyte, where anion-driven actuation (10% strain) was observed rather than the original cation-driven actuation. Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and scanning ionic conductance microscopy were applied to evaluate changes in morphology and electrochemical properties before and after the actuation cycles to examine changes in the actuation mode. The mechanism and reasons for the observed behaviour are proposed.