Trilayer actuators

Figure 15.1 Conducting-polymer actuation based upon bending of a bilayer or trIlayer actuator in which S-SO-jim-thick polymer layers are typically grown on a metal-coated Inert support the linear stretching of a free-standing film, of several mm to cm in length and the out-of-plane actuation of conducting-polymer films...

Trilayer PPy actuators have also been constructed in which PPy is electrodeposited on either side of a gold electrode using the large DBS ion on one side (cation-driven PPy) and a smaller benzenesulfonate on the other (anion-driven PPy), which bent quickly in a cooperative manner as the trilayer was oxidized or reduced in 1 M LiC104 [26]. A problem with any design in which the conducting-polymer remains attached to an inert metal... 

Conducting-polymer actuators have been developed for several applications by the Wollongong group [9]. These include the use of bUayer PPy actuators in a cochlear ear implant [85]. Hollow-tube actuators with helical wire interconnects have also been developed for use in an electronic Braille screen [39]. A trilayer actuator valve has been included in a combined sensor-actuator system to control a gas valve inlet for food... 

PPy doped with TFSl has also been used to create a fast bending trilayer actuator, based upon a gold-coated PVDF membrane operated in air, relying on high diffusion rates through the gel-like polymer, more so than the size of the polymer conductivity. Tip displacements peaked for certain actuation frequencies (between 4 and 90 Hz, depending... 

G. Alici and N.N. Huynh, Predicting force output of trilayer polymer actuators. Sens. Actuat A, A132 (2), 616-625 (2006). 

The trilayer PPy actuator is illustrated in Fig. 5.1. On both sides of the actuator are PPy layers. In the middle is an amorphous, porous pol3cvinyli-dene fluoride (PVDF) layer that serves both as a backing material and a reservoir for the electrolyte, which allows the actuator to work in air for a limited period of time (up to several hours). During the electrochemical deposition of the PPy layers, anions A in the electrolyte are introduced into the polymer matrix, which is a process called doping. When a voltage is ap-... 

Fig. 5.1 Illustration of a trilayer PPy actuator (a) Working principle of a trilayer bender the sectional view of the trilayer structure (left) and bending upon application of a voltage (right) (b) observed large bending deformation. Reprinted from [Fang and Tan (2010)1 with permission from Elsevier, Copyright 2010.

Trilayer PPy actuators were first reported by the Intelligent Polymer Research Institute at the University of Wollongong, Australia. A description of the fabrication process can be found in, e.g., [Wu et al. (2006)], and it is provided here for completeness. The PPy layers are electrochemically deposited on both sides of a gold-coated porous PVDF film. The PVDF film obtained from Sigma-Aldrich Co., has a thickness of 110 lam with pore size of 0.45 /Ltm. Gold layers of 100 nm are sputtered on both sides of the PVDF,... 

Fig. 5.2 Fabrication of trilayer PPy actuator (a) The fabrication setup (b) a fabricated sample. Reprinted from [Fang and Tan (2010)].

Experiments were conducted on trilayer PPy actuators to validate the effectiveness of the redox level-dependent admittance model. The electrolyte used was tetrabutylammonium hexafluorophosphate (TBA+PFg) in the solvent propylene carbonate (PC). The samples were predoped with PFg during fabrication, and the nominal concentration Co in the absence of DC bias was estimated to be fOOO mol/m based on the deposition conditions. In experiments different values of Cq were achieved by applying appropriate DC biases. Sinusoidal voltages of amplitude 0.05 V and frequency 0.08 — 200 Hz were superimposed on the DC voltage, as perturbations, for the measurement of admittance (or equivalently, impedance) spectra. 

Fig. 5.16 Inner bending radius of trilayer PPy actuators under different DC voltages (a) Sample with dimensions 13 x 5 x 0.17 mm (b) (a) Sample with dimensions 33 x 6 x 0.17 mm . Reprinted from [Fang et al. (2008a)j.

Fang, Y., Pence, T. J. and Tan, X. (2008a). Nonhnear elastic modeling of differential expansion in trilayer conjugated polymer actuators. Smart Materials and Structures 17, p. 065020. 

Fang, Y., Tan, X., Shen, Y., Xi, N. and Alici, G. (2008d). A scalable model for trilayer conjugated polymer actuators and its experimental validation. 

Wu, Y., Alici, G., Spinks, G. M. and Wallace, G. G. (2006). Fast trilayer polypyrrole bending actuators for high speed applications, Synthetic Metals 156, pp. 1017-1022. 

The bilayer deviee requires a eounter-electrode to allow the current flow, expending there most of the consumed electrical energy. Trilayer actuators (Fig. 2b) use two CP films, electrode and counter-electrode, with cooperative actuation due to opposed volume variations during current flow, increasing the effieieney of the aetuator (Han and Shi 2004 Ahci and Huynh 2006 John et al. 2008 Yao et al. 2008 Zainudeen et al. 2008 Garcia-Cordova et al. 2011). 

Empirical results Irom bending bilayer or trilayer actuators corroborate that the described angle (angle) is under linear control of the charge (Q) consxuned by the conducting polymer film reaction (Otero and Sansinena 1997 Otero and Cortes 2004 Conzuelo et al. 2010 Valero et al. 2011) ... 

Alici G, Huynh NN (2006) Predicting force output of trilayer polymer actuators. Sensors Actuators Phys 132 616 25. doi 10.1016/j.sna.2006.02.046... 

Sensors Actuators Phys 163 240-246. doi 10.1016/j.sna.2010.06.002 Fang Y, Tan X, Alici G (2008a) Robust adaptive control of conjugated polymer actuators. IEEE Trans Control SystTechnol 16 600-612. doi 10.1109/rCST.2007.912112 Fang Y, Tan X, Shen Y et al (2008b) A scalable model for trilayer conjugated polymer actuators and its experimental validation. Mater Sci Eng C Biomim Supramol Syst 28 421-428. doi 10.1016/ j.msec.2007.04.024... 

Trilayer Polymer Actuator (a monolithic active mechanism)... 

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