Monolithic Actuators from Flash‐Welded Polyaniline Nanofibers

Abstract

Asymmetric films formed by flash-welding polyaniline nanofiber mats demonstrate rapid reversible actuation in the presence of select aqueous acids and bases. These continuous single component bending/curling actuators have several advantages over conventional dual component, bimorph actuators including ease of synthesis, large degree of bending, patternability and no delamination. The films are made through a controlled, facile, all aqueous process that yields water dispersed polyaniline nanofibers that are readily cast into films. Flash welding photothermally cross-links and melts the top surface of the nanostructured polymer producing an asymmetric film. The resultant cross-linked surface is quite dense and has a reduced number of protonic acid doping sites available. The film surface is therefore less susceptible to the protonic acid doping which expands the underlying high surface area nanofiber layer. Actuation occurs at a comparable or faster rate than bimorph actuators with an unprecedented > 720°bending relative to the initial flat position for a 2.5 cm length film. The collective movement of the individual nanofibers in the asymmetric film creates a large degree of actuation resembling natural muscle. These bending actuators could be developed for use in microtweezers, microvalves, artificial muscles, chemical sensors and/or patterned actuator structures.Polyaniline and other conducting polymers have been of interest for their actuation properties for more than two decades. [1][2][3][4][5][6][7][8] The actuation is due to the unique chemistry of conducting polymers, which generally swell reversibly with the incorporation of dopant ions and their associated solvent molecules. 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. One material forms the active part that expands or contracts relative to the inactive part upon stimulation, thus inducing bending. 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. Doping induced swelling ...

Giving Direction to Motion and Surface with Ultra‐Fast Speed Using Oriented Hydrogel Fibers

“…The pioneering work of Hu et al [ 16 ] regarding actuation based on differential swelling/shrinking of two layers triggered by water and temperature in a bilayer polymeric system remains the basis of thermoresponsive polymeric actuators, highly interesting for applications in tissue engineering, cell High porosity was utilized in providing fast actuation to polymeric actuators with acetone, camphor sulphonic acid, ethanol, and sodium hydroxide as solvents. [ 2,21,25 ] We recently showed the fastest temperature-triggered bilayer polymeric actuators, with a thickness of more than 100 µm and planar size of 25 × 5 mm, reversibly bending and rolling to tubes in less than 1 s. [ 26 ] But a still unresolved challenge is to control the direction of movement without sacrifi cing instant/fast reversible large-scale actuation. We addressed the issue and in this work, present a large size temperature-triggered polymeric actuator with control in the direction of movement at ultra-fast speed, i.e., ≈0.6-5 s depending upon the type of movement.…”

EC-AFM investigation of reversible volume changes with electrode potential in polyaniline

“…Among these polyaniline (PANI) is one of the most important owing to its stability, easy synthesis and optical properties. This has led to many research efforts for applications of PANI in various fields such as actuators [4,5], fuel cells [6], supercapacitors [7,8], biosensors [9,10], electrocatalysis [11], and photovoltaic devices [12]. PANI has been used as transducer material for sensors as its electrical property strongly depends on the electrochemical potential and its rapid equilibrium with protons in the medium [13][14][15].…”

Covalent attachment of functional side-groups to polyaniline nanofibres

“…These one-dimensional objects combine the advantages of an organic conductor with those of a high surface area material, thus making them ideal for a diverse range of applications such as electronic devices, chemical sensors and actuators (Huang et al, 2003;Virji et al, 2004Virji et al, , 2005aVirji et al, , 2005bVirji et al, , 2006Small et al, 2007;Baker et al, 2008;Roh et al, 2002). Polyaniline (PAni) is an example of a conducting polymer, which can be switched between distinct states that exhibit dramatically different properties.…”