Mixed-ion linear actuation behaviour of polypyrrole

Conducting polymer bending actuators show potential for unique manipulation devices, particularly at the microscale, given low actuation voltages, controllable manufacture, biocompatibility, and ability to operate in either air or liquid environments; however, the impracticalities of implementing feedback in these environments and at these scales can impede positional control of the actuator. This paper presents an application of inversion-based feedforward positional control to a trilayer bender actuator, which is shown to improve the performance without the use of feedback or adjustments to the chemistry of the device. The step and dynamic displacement responses have all been improved under the feedforward control system, while the response does not change significantly under large increases in external loads. This study contributes the first implementation of inversion-based feedforward control to the emerging area of conducting polymer actuators, paving the way toward their use in functional devices, particularly where the implementation of feedback is difficult.

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Inversion-Based Feedforward Control of Polypyrrole Trilayer Bender Actuators

In situ observation of dynamic elastic modulus in polypyrrole actuators

The actuation properties of free standing PPy films polymerised from propylene carbonate (PC) solutions of tetrabutylammonium triflouromethanesulfonate (TBACF3SO3) and tetrabutylammonium hexaflourophosphate (TBAPF6) electrolytes were investigated by means of electrochemomechanical deformation (ECMD) measurements during cyclic voltammetry (CV) and chronoamperometry. The ECMD properties of the films were studied in PC/TBAPF6 and PC/TBACF3SO3 electrolytes to determine the effect of both the preparation and cycling electrolytes. Most systems showed mixed-ion actuation, although PPy/TBACF3SO3 films exhibited greater cathodic actuation. However, the extent of anodic actuation exceeded the cathodic actuation in all cases. When the cycling electrolyte was different from the preparation electrolyte it was found that the size of the anion at preparation had a critical effect: smaller PF6− anions in PPy/TBAPF6 films cannot be easily ion-exchanged for the larger CF3SO3−, which also had a tendency to stay entrapped in the polymer network, resulting in decreased anodic actuation and an increase in cathodic (cation-driven) actuation. On the contrary, significant cathodic movement for PPy/TBACF3SO3 films was suppressed when the cycling electrolyte was changed to PC/TBAPF6. Chronoamperometry was used to examine the kinetics of actuation in the positive potential region and electrochemical potential step experiments to investigate the long-term stability of the studied systems.

Actuation of polypyrrole films in propylene carbonate electrolytes

The deflection of the electrochemically grown poly(3,4-ethylenedioxythiophene) (PEDOT) bilayers was shown to depend greatly on the polymerisation potential, as established by measurements of bilayer deflection during chronoamperometry experiments. The reproducibility was tested by polymerising PEDOT bilayers at least three times at the same polymerisation potential. Therefore, PEDOT bilayer films obtained at low polymerisation potentials showed high deflection at oxidation, high actuation speed and good durability, while those values decreased for bilayer films obtained at higher polymerisation potentials. Long term cycling characteristics for a PEDOT bilayer polymerised at a low polymerisation potential (1.05 V versus Ag/AgAgCl) were tested by actuating the film in 11,000 cycles.

Effect of electrochemical synthesis conditions on deflection of PEDOT bilayers

The use of bimorph actuators based on conducting polymers (CP) in an integrated oxygen control system is explored with practical focus on the control of a fruit storage atmosphere at 5% oxygen. A low-cost oxygen sensor is integrated with a simple actuator valve to limit the influx of atmospheric oxygen to the storage package. For this task, electrochemical oxygen sensors as used in the study, such as zinc–air cells with output potentials up to 1 V, appear to be well suited to drive trilayer strips based on CPs that actuate over a similar range. The actuator used, based on polypyrrole (Ppy), gave reliable and repeatable mechanical behaviour for about 50 h. Two sensor–actuator systems have been trialled. In one, the output from a lead-oxygen sensor was electronically augmented to drive a conducting polymer trilayer actuator valve. The desired oxygen concentration was easily maintained with response times of tens of seconds. The other system used the output from a zinc–air cell directly to drive an actuator valve that limited the diffusion of air into the enclosure. Positive oxygen concentration control was achieved but at lower rates of oxygen flux and longer response times. Good sealing of the orifice at closure was found to be critical.

Murray L. Jansen

Papers

An integrated electrochemical sensor–actuator system