A composite system comprised of polyaniline nanofibers bonded with gold nanoparticles is shown to possess a memory effect via a charge transfer mechanism. The charge transfer occurs between the imine nitrogen in the polyaniline and the gold nanoparticles as confirmed by x-ray photoelectron spectroscopy and Raman spectroscopy. This charge transfer enables a bistable electrical conductivity, allowing the material system to be used as a digital memory device. The charge transfer is further confirmed by the elimination of the conductance switching when the fully reduced form of polyaniline, leucoemeraldine, which possesses no imine nitrogens, is used in place of the emeraldine form.

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 ...

Controlling reaction temperature for a set time enables the size of gold nanoparticles autoreduced on the surface of polyaniline nanofibers to be controlled. The size of the gold nanoparticles can be used to tune the electrical bistable memory effect in gold/polyaniline nanofiber composite devices. Turn-on voltages and on/off ratios improve with decreasing nanoparticle size, making this a promising method to enhance performance and create smaller devices. Long-term stability of the composites can be improved by the addition of stabilizers following autoreduction of the gold nanoparticles.

Zinc oxide (ZnO) nanoparticles functionalized with a bi-functional coupling agent methacryloxypropyl-trimethoxysilane (MPS) were used to fabricate a vinyl-ester resin polymeric nanocomposite, which shows an improved interfacial interaction between the particle and matrix. As a result, in comparison to the unmodified particle-filled nanocomposites, the functionalized particle-filled composites possessed higher resistance to thermal degradation, and demonstrated improved UV shielding and enhanced photoluminescent properties. The more uniform particle dispersion, passivation of the particle surface with MPS and increased oxygen vacancies were justified to contribute to the increased thermal stability and the enhanced photoluminescent properties. Significant tensile strength improvement was closely related to the observed uniform particle distribution and the intimate interfacial interaction through the strong chemical bonding