An actuating system composed of nafion ionomeric polymer coated with single-walled carbon nanotubes electrodes was studied as an electromechanical actuator. The actuator gives a sizable mechanical response to low voltages (turn-on voltage of approximately 2.5 V) under open-air conditions, i.e., in the absence of a surrounding supporting electrolyte. The actuator is active under both dc and ac bias and has a strong resonance at low frequencies which is dependent upon the size of the actuator. The actuator was studied using Fourier transform infrared and vis-NIR spectroscopies, cyclic voltammetry, and by the current-time response under an applied step voltage. An analytical model is proposed to understand the electrical behavior, which is consistent with the spectroscopic results.

A bilayer composite of single walled carbon nanotubes (SWNTs) deposited onto Nafion exhibits substantial mechanical motion upon exposure to visible or near-infrared light. The magnitude of the actuation parallels the absorption spectrum of the SWNTs in the near-infrared, but the actuation diminishes in the visible and disappears in the UV portions of the spectrum. In the near-infrared region, the photoactuation is linear with respect to the light intensity. The photoactuation also appears to be associated with a photocurrent across the nanotube/Nafion interface. The proposed mechanism for the actuation is that band bending of the semiconducting SWNTs induces polarization of mobile hydrogen ions at the Nafion interface, which then causes swelling of the polymer.

We report the fabrication and characterization of a novel composite material based on single walled carbon nanotubes (SWNT)s and the ionomeric polymer Nafion. SWNTs were airbrushed from a chloroform suspension onto both sides of a Nafion membrane (180 µm) and the electromechanical properties of the composite material were explored. The outer layers of carbon nanotubes acted as electrodes in order to pass electrical current through the system while the mechanical response was monitored. Under this design, the mechanical response could be characterized, with respect to the electrical signal, as a function of: voltage, waveform (AC vs. DC), and frequency (AC). Data was also compiled to gauge the effect of size and thickness of each individual layer of the system. The reference samples (graphite-Nafion and sputtered goldNafion) did not exhibit mechanical actuation at the same conditions. An analytical model for current decay was considered that is in agreement with the experimental data. Bi-exponential decay with a long time component was found for bias, which is above the actuating threshold. That was explained in terms of increasing of the water dielectric constant and polymer-SWNT interface area. The possible mechanisms of the actuation in this novel composite are discussed.

The photoconductive response of single-walled carbon nanotubes (SWNTs) has been studied under CW illumination in the NIR (900 -1800 nm) and far-IR (9-10 pm) range. SWNTs were coated onto patterned gold electrodes with spacing which was varied from 5 to 300 nm. SWNT samples exhibit absorption NIR bands that are typical for semiconducting nanotubes with a diameter distribution o f 0 3 -1.1 nm and band at -10 pm in the far4R range. A clear correlation between current and IR exposure has been observed. The detection of photoconductivity requires instrumentation with a high dynamic range due to a significant dark current. The photocurrent exhibits a linear response with light intensity and with bias voltage. Possible mechanisms of photoconductivity in SWNT films and applications of this new photosensitive material are discussed. I. INRODUCTIONThe large amount of attention placed on the electronic and optical properties of single-walled carbon, nanotubes (SWNTs) is associated with both the nanotuhe well-defined ID structure and the possibility of employing them as building blocks for various nanotechnoloa applications [I].In particular, the interaction of light with the nanotube structures is a matter of special interest due to the opportunity to observe new photophysical effects related to the nanotube low dimensionality and quantum confinement. For the past several years, numerous studies have been performed in the field of nanotube light absorption [2-4], Raman scattering [I, 51, fluorescence [4, 61, photoinduced molecular desorption [7], and electroluminescence [SI. Nevertheless, the SWNT photoconductivity remains a practically non-explored area: a temporal photocurrent was detected in the fust reported observation of SWNT mat photoconductivity using pulsed laser excitation [9]. Such scarce information hints that observation of steady-state SWNT photoconductivity can be hampered by obstacles related to low light absorption of the nanotubes andlor a high level of dark cumnt due to the metal conductivity masking the semiconductor properties [I]. Thus, the SWNT photoconductive response under steady state or continuous wave (CW) illumination presents interest not only for a fundamental understanding of SWNT photoinduced processes, but also for the development of a new photosensitive material with unique optical and conductive features. In this paper we report the fust observation of CW photoconductivity of single-walled carbon nanotubes in the NIR and far-IR spectral range.11. EXPERIMENT SWNTs were synthesized by the arc discharge method and purified (85%) using air oxidation, acid treatment and thermal annealing, as purchased from BuckyUSA, Inc. The average diameter of the most nanotubes was in the range of 0.8 -1.1 tun according to NIR spectroscopy and TEM observation. However, as it was found from FTIR spectra, that some SWNTs have significantly larger diameter (7-8 nm) with the absorbance band at -10 pm.For the photoconductivity study, a nanotube suspension in methanol was sonicated followed by dropping a small amo...

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