DOE OSTI2015
An actuating material system comprising a gold-film with nanotextured surface was fabricated. Using electroless gold plating onto a substrate of porous anodized aluminum oxide, a thin film of gold with a high density of short gold nanofibers on its surface was made. When one end of such a film was connected to an ion generator, bending was achieved upon electrical charging in air. Experiments showed that the free end of an 8 mm film could be displaced by more than 1.6 mm with a bending strain of 0.08%. In contrast with other types of thin-film artificial muscle materials, the present Au-film did not require any electrolyte to function. With the relatively easy fabrication method, this nanotextured film shows promising actuation behavior in air. Actuation systems based on a number of mechanisms have been developed in the last few decades, including electric, ionic, photonic, pneumatic, and thermal. As discussed in detail in Madden et al. and Brochu and Pei,11 the weaknesses of these materials include bulkiness, low stress or strain generation, low strain rate, long response time, short cycle life, and low energy efficiency. Recent developments have involved the possibilities to use the unique properties of nanostructures to produce actuation, such as in nanostructured carbon, nanoporous gold or platinum, V 2 O 5 nanofibre sheet, electroactive nanostructured polymers, hybrid carbon nanotube yarn, niobium nanowire yarn, and anodized aluminum oxide (AAO). Here, we introduce a nanostructured material system comprising a gold film with a high density of short gold-nanofibers attached to one side, which can bend to produce a large displacement (~1.6 mm) upon electrical charging through an ion generator. In addition to the displacement, the functionality without the need of an electrolyte is another advantage for using this material system as actuators. We discuss the fabrication and characterization methods, the morphology, and the actuating properties of this system here. To achieve a metal film with a nanotextured surface, electroless gold-plating was performed on substrates of AAO with a characteristic nano-honeycomb structure consisting of >10 10 pores per cm 2 . The fabrication of the AAO substrates followed the procedures described in Cheng and Ngan. The anodization condition for the AAO was 40 V against graphite electrode in saturated oxalic acid at 18 °C for 2 h. The pore diameter observed was 50 ± 5 nm. By using an electroless gold-plating method described by Kohli et al.,22 gold in short nanofiber form was deposited into the pores of the AAO template. As shown in Figs. 1(a) and 1(b), in addition to partially filling the pores with gold, the top surface of the AAO template was coated with a thin gold film (~100 nm) of Au. A ~30 μm layer of lacquer was then painted on the top of the thin gold film to serve as a supporting layer.