Application of conducting polymers has been growing widely in different fields such as batteries, solar cells, capacitors
and actuators. Mechanical properties of conducting polymers like flexibility, high power to mass ratio and high active
strain make them potentially applicable to robotic and automation industries. Obviously, a dynamic model of the
actuation phenomenon in conducting polymers is needed to study its controllability and also to optimize the mechanical
performance. De Rossi and colleagues suggest treating the mechanical behaviour of conducting polymers separately
from the viscoelastic structural model and electrochemical actuation. But it has been observed that the effects of
electrochemical actuation and diffusion of ions on the viscoelastic coefficients cannot be neglected in some conducting
polymer actuators, as shown in. In this paper, we present the effects of cyclic voltammetry actuation on shear modulus
of polypyrrole in propylene carbonate and EMI.TSFI as measured by an electrochemical Quartz Crystal Microbalance
(eQCM). The QCM consists basically of an AT-cut piezoelectric quartz crystal disc with metallic electrode films
deposited on its faces. One face is exposed to the active medium. A driver circuit applies an AC signal to the electrodes,
causing the crystal to oscillate in a shear mode, at a given resonance frequency. QCM has been routinely used for the
determination of mass changes. Measured resonance frequency shifts are converted into mass changes by the wellknown
Sauerbrey's equation. In this paper, we correlate the admittance output of QCM to the real shear modulus of
polypyrrole. Then the results of the correlation which contains mechanical data are presented during actuation using two
different types of electrolyte.
Conducting polymer actuators are being investigated for a number of applications. Both linear contracting/expanding and bending type actuators can be constructed that utilise the redox-induced volume changes in the conducting polymer. Improved actuator performance has been demonstrated by modifications to our helix-tube design. The pitch of the helix and bundling the actuators have increased the strain and force generated. Short-term improvements to the strain were also generated using new dopants, but cycle life was poor in this case. Further studies on the mechanism of actuation have continued to focus attention on the influence of the elastic modulus on the actuation strain. Surprising results have been obtained from polythiophene actuators that show an increased strain and increased work-per-cycle with an increasing applied load in isotonic operation. The observations were explained by an increase in modulus during the contraction cycle of the actuation. Preliminary studies show how the change in modulus can be conveniently measured using an in situ mechanical technique.
The phase inversion technique was used to produce polyaniline (PAn) actuators with different geometries that cannot be obtained by PAn cast from N-methyl-2-pyrrolidinone (NMP) solution in a conventional way. PAn was cast and coagulated in a water bath forming films and tubes with or without a platinum (Pt) wire helix as an interconnect. PAn was doped with hydrochloric solution (HCl, 1 M) (PAn/HCl) or methanesulfonic acid (MSA, 1 M) (PAn/MSA). In nitric acid (HNO3, 1 M) aqueous electrolyte, the actuation strain of PAn/HCl was 0.9% which increased to 2.0% and 2.7% for the tubes without and with the Pt helix, respectively. The Pt helix helped prevent the IR drop along the actuator. Comparing with NaNO3 (1 M) aqueous electrolyte, the use of HNO3 aqueous electrolyte gave better actuation stability where at least 100 cycles were observed and the final actuation strain was determined by the size of dopant. Change of coagulation bath from water to NMP (30% w/w)/water resulted in subtle difference in the Young’s modulus of PAn/MSA in oxidized and reduced states. PAn prepared by phase inversion technique is porous by nature, consequently it is brittle and exhibits a low actuation stress (0.3 - 0.4 MPa).
Polythiophene, one of the most extensively studied conducting polymers, was selected as an actuator material due to its chemical and electrochemical stability both in air and moisture. In this work, poly(3-methylthiophene) based actuators were constructed electrochemically with a tubular geometrical configuration. The actuation behaviour was investigated regarding to the actuation strain generated, the stress produced and work per cycle performed by poly(3-methylthiophene) actuators. The effect of potential sweep rate and different electrolytes (ionic liquid and organic solvent) on the actuation performance were also explored. Poly(3-methylthiophene) actuators show an increase in actuation strain with an increase in applied load.