Small, highly-mobile "swimming" robots are desired for underwater monitoring operations, including pollution
detection, video mapping and other tasks. Actuator materials of all types are of interest for any application where space
is limited. This constraint certainly applies to the small-scale swimming robot, where multiple small actuators are
needed for forward/backward propulsion, steering and diving/surfacing. A number of previous studies have
demonstrated propulsion of floating objects using IPMC type polymer actuators [1-3] or piezoceramic actuators [4, 5].
Here, we show how propulsion is also possible using a multi-layer polypyrrole bimorph actuator. The actuator is based
on our previously published work showing very fast resonance actuation in polypyrrole bending-type actuators [6].
The bending actuator is a tri-layer structure, in which the gold-PVDF (porous poly(vinylidene fluoride) membrane)
substrate was coated on both sides with polypyrrole layers to form an electrochemical cell. Polypyrrole films on gold
coated PVDF were grown galvanostatically at a current density of 0.10 mA/cm2 for 12 hours from propylene carbonate
(PC) solution containing 0.1 M Li+TFSI-, 0.1 M pyrrole and 1% (w/w) water. The polypyrrole deposited PVDF was
thoroughly rinsed with acetone and stored in 0.1 M Li+TFSI- / PC solution. The edges of the bulk film were trimmed
off and the bending actuators were prepared as rectangular strips typically 2mm wide and 25 mm long.
These actuators gave fast operation in air (to 90 Hz), and were utilised as active flexural joints on the tail fin of a fishshaped
floating "boat". The actuators were attached to a simple truncated shaped fin and the deflection angle was
analysed in both air and liquid for excitation with +/- 1V square wave at a range of frequencies. The mechanical
resonance of the fin was seen to be 4.5 Hz in air and 0.45 Hz in PC, which gave deflection angles of approximately 60°
and 55° respectively.
The boat contained a battery, receiver unit and electronic circuit attached to the actuator fin assembly. Thus, the boat
could be operated by remote control, and by varying the frequency and duty cycle applied to the actuator, the speed and
direction of the boat could be controlled. The boat had a turning circle as small as 15 cm in radius and a maximum
speed of 2m/min when operating with a tail frequency of approximately 0.7 Hz. The efficiency of the flapping tail fin
was analysed and it was seen that operation at this frequency corresponded with a Strouhal number in the optimal range.
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.
Designing and building devices that utilize electroactive polymer actuators brings into sharp focus the performance required of these materials. Using the example of a "rehabilitation glove", it is shown that the performance of polypyrrole actuators fall short of that required. In particular, the need to simultaneously produce 5% actuator strain at a 5 MPa isotonic stress cannot be achieved with the actuators investigated in our laboratories to date. However, significant improvements in the performance under load have been achieved with the use of ionic liquid electrolytes. The use of new materials such as composites of conducting polymers and carbon nanotubes offers the possibility of further improvements in actuator performance. Finally, redesigning the glove actuator offers a compromise solution that allows existing actuators to be used in a prototype device.
There is a great need to develop a computer screen based on Braille technology that allows blind people to access computer-based information to the same extent as sighted people. The lack of a "graphical user interface" for the blind severely restricts employment, educational and recreational opportunities readily available to sighted people in the "internet age". Equally, the development of a refreshable 2-D Braille screen offers the EAP community a great opportunity to make a tremendous impact with new actuator technology. In this paper we review progress made in the development of a prototype multi-dot Braille cell using conducting polymer actuators. Two innovations (a helical wire interconnect and ionic liquid electrolytes) have provided significant performance advances in terms of strain rate and cycle lifetime, respectively. Despite these advances, some further challenges remain.
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