Electrochemical actuation properties of a novel solution-processable polythiophene

A solution-processable polythiophene, poly((E)-4,4″-didecoxy-3′-styryl[2,2′:5′,2′′]terthiophene) demonstrated large electrochemically induced strain up to 11.5%. Free-standing polymer films were characterised using four-point probe conductivity measurements, cyclic voltammetry and electrochemical actuation measurements. Conductivities of ∼6 × 10−5 S/cm (reduced state) or ∼1–2 S/cm (oxidised state) were measured. Well-defined polymer oxidation–reduction responses were observed in both the propylene carbonate and acetonitrile electrolytes, with electrochemical efficiency of >80% observed under ideal conditions. Results obtained suggested that the actuation strain approximately correlates with the size of the anion (i.e. TFSI > PF6− > ClO4−) used in the electrolyte. The largest strain ∼11.5% was obtained in an electrolyte solution consisting of 0.1 M Li.TFSI in acetonitrile. The maximum strain attainable increased with an increase in the anodic potential applied and decreased with an increase in stimulation frequency or increasing mechanical load. Such functionalised polythiophene material has the combined advantage of solution processability and the ability to produce large strain.