Electrochemical actuators

In recent several years, super-capacitors are attracting more and more attention because of their high capacitance and potential applications in electronic devices. The performance of super-capacitors with MWCNTs deposited with conducting polymers as active materials is greatly enhanced compared to electric double-layer super-capacitors with CNTs due to the Faraday effect of the conducting polymer as shown in Fig. 9.18 (Valter et al., 2002). Besides those mentioned above, polymer/ CNT nanocomposites own many potential applications (Breuer and Sundararaj, 2004) in electrochemical actuation, wave absorption, electronic packaging, selfregulating heater, and PTC resistors, etc. The conductivity results for polymer/CNT composites are summarized in Table 9.1 (Biercuk et al., 2002). 

The fabrication of supercapacitors and electrochemical actuators that could be used as artificial muscles is another alternative for nanotube applications. Supercapacitors already were built on hybrid vehicles because this could provide rapid acceleration and store braking energy electrically. When using sheet electrodes with SWNT and MWNTs, it is possible to obtain specific capacitance of 180 and 102 F/g and power densities of 20 and 8kW/kg, respectively. 

Mirfakhrai T, Madden JDW, Baughman RH (2006) Electrochemical actuation of carbon nanotube yams. Smart Mater Stmct 16 S243... 

Kaneto K, Kaneko M, Min Y, MacDiarmid AG (1995) Artificial muscle-electrochemical actuators using polyaniline films. Synth Met 71 2211... 

Lewis TW, Kane-Maguire LAP, Hutchinson AS, Spinks GM, Wallace GG (1999) Development of an all-polymer, axial force electrochemical actuator. Synth Met 102 1317... 

Figure 15.8 SEM image of a PANI membrane prepared by the phase inversion technique with the appearance of macrovoids. (Reprinted with permission from Advanced Functional Materials, High-performance, monolithic polyaniline electrochemical actuators by j.-M. Sansinena, J. Gao and H.-L. Wang, H.-L., 13, 9, 703-709. Copyright (2003) Wiley-VCH)...

G. Han and G. Shi, High-response tri-layer electrochemical actuators based on conducting polymer films, J. Electroanal. Chem., 569 (2), 169-174 (2004). 

G. Han and G. Shi, Conducting polymer electrochemical actuator made of high-strength threelayered composite films of polythiophene and polypyrrole. Sens. Actual. B, B99 (2-3), 525-531... 

X. He and G. Shi, Electrochemical actuator based on monolithic polypyrrole-Ti02 nanoparticle composite film. Sens. Actual. B, B115 (1), 488-493 (2006). 

B. Xi, V.-T. Truong, P. Whitten, J. Ding, G.M. Spinks, G.G. Wallace, Poly(3-methylthio-phene) electrochemical actuators showing increased strain and work per cycle at higher operating stresses. Polymer, 47 (22), 7720-7725 (2006). 

However, the electrochemical actuators made Irom conducting polymers still suffered from the short cyclic lifetime and slow responsiveness. In particular, compared with the dry-state counterparts, the mechanical performances of the conducting polymers in electrolyte media are significantly degraded (Spinks et al., 2006) which significantly limits the practical applications. 

Kong, L.R., Chen,W., 2014. Carbon nano tube and graphene-based bioinspired electrochemical actuators. Adv. Mater. 26,1025-1043. 

Biochemical analysis on nanoliter scale is precisely carried out by micrototal analysis system (pTAS) which consists of microreactors, microfluidic systems, and detectors. Performance of the pTAS depends on micromachined and electrochemically actuated micropump capable of precise dosing of nanoliter amounts of liquids such as reagents, indicators, or calibration fluids [28]. The dosing system is based on the displacement of the liquid from a reservoir which is actuated by gas bubbles produced electrochemically. Electrochemical pump and dosing system consist of a channel structure micro-machined in silicon closed by Pyrex covered with novel metal electrodes. By applying pulsed current to the electrodes, gas bubbles are produced by electrolysis of water. The liquid stored in the meander is driven out into the microchannel structure due to expansion of gas bubbles in the reservoir as shown in Fig. 11.8. 

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