Fabrication and Characterization of Polyaniline Monolithic Actuators Based on a Novel Configuration:  Integrally Skinned Asymmetric Membrane

Abstract

We report the synthesis and characterization of polyaniline integrally skinned asymmetric membranes (PANI ISAMs) and their use as chemical and electrochemical actuators. SEM characterization of a PANI ISAM cross section showed a thin dense skin and a microporous substructure with a PANI density gradient. The deformation mechanism of chemical monolithic PANI ISAM actuation was found to result mainly from asymmetric volume expansion/contraction because of the presence/absence of counterions during PANI doping/dedoping cycles. Actuator performance was affected by acid concentration and film thickness. Our results also show that the deformation mechanism in electrochemical PANI ISAM actuation involves mainly changes in polymer conformation with changes in oxidation state. Because these PANI ISAM actuators are monolithic, that is, they are fabricated without any additional layer (tape, polymer, or gold), their structural stability is expected to be superior to bimorph actuators.

Biomimetic Sensing – Actuators Based on Conducting Polymers

“…It is possible to obtain bending movement from asymmetrical monolayers of the same CP, having an internal asymmetry capable of producing asymmetric swelling or shrinking across the film under the same electrochemical process (doping or de-doping) (Okamoto et al 2000;Onoda et al 1999a;Onoda & Tada 2004;Onoda et al 1999b;Shakuda et al 1993;Takashima et al 2003b;Takashima et al 1997;Wang et al 2002): one half of the film has a prevalent anionic exchange, while the second half experiences a prevalent cationic exchange. This can be achieved in two separate stages of electrogeneration using different dopants for the same polymer.…”

“…A metallic counter electrode is required. Other possibilities are being explored to produce asymmetric monolayers by physical means, for example, by growing the CP on adsorbed and porous materials (Li et al 2004), or by electrochemical means generating a film of CP with a counterion concentration gradient (Okuzaki & Hattori 2003;Sansiñena et al 2003;Shakuda et al 1993;Wang et al 2002), conductivity (Nakano & Okamoto 2001;Onoda et al 2005) or morphology gradients (Han & Shi 2006;Okamoto et al 2001;Onoda & Tada 2004) by crosslinking network, or by generating a bilayer of the conducting polymer with a macroanion (shrinks by oxidation) and then of the same conducting polymer with a small anion (swells by oxidation) (Han & Shi 2006;Takashima et al 2003a), or even placing a metal sheet between both films (Han & Shi 2004b). As in the case of bilayer devices, asymmetric films also need an electrolyte and a metallic counter electrode in order to allow the flow of the current and to produce the bending movement.…”

Simultaneous Smart Actuating-Sensing Devices Based on Conducting Polymers

“…In a similar way it is possible to obtain bending movement from asymmetrical monolayers of the same conducting polymer, having an internal asymmetry capable of producing asymmetric swelling or shrinking across the film under the same electrochemical process (Okamoto et al, 2000;Onoda et al, 1999a;Onoda & Tada, 2004;Onoda et al, 1999b;Shakuda et al, 1993;Takashima et al, 2003;Takashima et al, 1997;Wang et al, 2002). Here half of the film has a prevalent anionic exchange, while the second half experiences a prevalent cationic exchange.…”

Monolithic Actuators from Flash‐Welded Polyaniline Nanofibers

“…Previous work on polyaniline actuators has involved dispersing conventional polyaniline in highly polar solvents such as N-methyl pyrrolidinone for casting into fibers, [9][10][11] rods, [12][13][14] sheets, [5] layered bimorphs [15,16] and integrally skinned asymmetric membranes. [7,[17][18][19] Elongation or contraction of polyaniline films and fibers has been induced by oxidation state, electrostatic or conformational changes as well as combinations of all of these to create linear or bending movement depending on the initial structure. Typical bending actuators require the use of two or more different materials bound together to produce a bimorph.…”

“…Bending of bimorph structures has generally been limited to < 90°and problems with adhesion between the layers often leads to delamination especially with extended use. [20] Alternative bending structures have been proposed such as active dual layers, which expand and contract cooperatively.[21] Wang, et al [7] made a major advance by developing integrally skinned asymmetric membrane (ISAM) bending polyaniline actuators. ISAMs use a single material processed so that one side of the film has much higher porosity than the other side.…”