Carbon Nanotube/Polyelectrolyte Composites as Novel Actuator Materials

Abstract

Mechanical actuators that simultaneously provide high power densities and large force generation capacities are of great scientific and technological interest. Recently single wall carbon nanotube (SWNT) papers ("bucky" papers) were shown to possess significant promise as electrochemical actuators. Embedding polyelectrolytes, like Nafion, within the nanotube matrix has the potential to address the limitations of SWNT bundling and tube slippage thus increasing force generation. In this paper two types of Nafion/SWNT composite actuators have been investigated depending on the method of fabrication. In the first case, infiltration of Nafion within SWNT paper matrix was followed by annealing at 150 °C to invert Nafion's micellar structure and render it insoluble. This has resulted in a substantially exfoliated layer morphology that causes a reduction in both conductivity and actuation strain (c.a. 0.03%). In the second case, slow casting of a methanolic suspension of Nafion and SWNT soot, followed by annealing at 150 °C, resulted in a more homogeneous structure. This composite, upon electrochemical cycling between -1 and +1 V in aqueous electrolytes, exhibited actuation strains (as high as 0.43%). However, these higher strains are accompanied by an order of magnitude reduction in modulus largely due to Nafion swelling.

Fibrillar Structure of Nafion: Matching Fourier and Real Space Studies of Corresponding Films and Solutions

“…As drawn in Figure 1c, we can describe the electron density or the phase variation observed along the fibrils in TEM or in AFM respectively as, in a first approximation, an oscillation in size or in density (or both) along the cylinder axis. We will see further in the article that a model of a necklace particle which has been already considered for a low charge polyelectrolyte 65,66 allows one to describe the scattering intensity modulation in the Nafion film spectra as well.…”