OTHER ELECTROCHEMOMECHANICAL ACTUATION

Baughman et al. [726] discussed in detail the merits of CP-based electrochemo-mechanical actuators as compared to other electromechanical actuators, e.g. those based on piezoelectrics. They noted, for instance that the voltages required for the CP-based actuators and a piezoelectric polymer such as poly(vinylidene fluoride) were of the order of single volts and tens of volts respectively, whilst the fraction length I change, AL/L, obtained with the former were 10%, whereas that with the latter Ws ca. 0.1%. 

Baughman et al. however also noted the considerable disadvantages of CPs their cyclability (just 100 cycles or so according to the work of Otero et al. cited above), as compared to possibly millions of cycles obtainable with piezoelectric materials and response time- of the order of seconds or tens of seconds, as compared to ms or even (is for piezoelectric materials. It would clearly be such factors which would limit commercial application of CP-based actuators. 

Smela et al. [929] constructed CP unimorph hinges, of dimension ca. 90 X 90 /tm, and used these to rotate paddles of dimension 900 X 900 (im in solution, as shown in Fig. 21-3. This would be the equivalent of a human arm moving a 30 X 30 m plate in water. They also used a P(Py)/Au bilayer to construct a microscopic box actuator , as shown in Fig. 21-4. 

BLACK Polypyrole/gold cantilever actuator RED Rigid,inactive polymer 

Actuators with similar action but based on P(ANi) single fibers have also been described [928], However, some of the applications envisioned for these, such as steerable optical fiber catheters for medical applications, seem a bit premature for the level of development achieved. 

---

Researchers are facing difficulties in attempts to improve properties and response rates of chemomechanical and electrochemomechanical systems based on polymer gels or proteins for practical applications as actuators in robotics. Lack of mechanical toughness and long-term durability are other problems to be solved. The efficiency of energy conversion must also be improved. New polymers that can link reversible chemical reactions to changes in volume are required to produce electrochemomechanical devices of practical interest. From a conceptual point of view, deep discussions are required to clarify and differentiate between chemomechanical, electromechanical, electroosmotic, electrophoretic driven, and electrochemomechanical devices. The main problem is to differentiate the presence and absence of chemical reaction. 

---