RESUMO
The combination of smooth, continuous sound spectra produced by a sound source having no vibrating parts, a nanoscale thickness of a flexible active layer and the feasibility of creating large, conformal projectors provoke interest in thermoacoustic phenomena. However, at low frequencies, the sound pressure level (SPL) and the sound generation efficiency of an open carbon nanotube sheet (CNTS) is low. In addition, the nanoscale thickness of fragile heating elements, their high sensitivity to the environment and the high surface temperatures practical for thermoacoustic sound generation necessitate protective encapsulation of a freestanding CNTS in inert gases. Encapsulation provides the desired increase of sound pressure towards low frequencies. However, the protective enclosure restricts heat dissipation from the resistively heated CNTS and the interior of the encapsulated device. Here, the heat dissipation issue is addressed by short pulse excitations of the CNTS. An overall increase of energy conversion efficiency by more than four orders (from 10-5 to 0.1) and the SPL of 120 dB re 20 µPa @ 1 m in air and 170 dB re 1 µPa @ 1 m in water were demonstrated. The short pulse excitation provides a stable linear increase of output sound pressure with substantially increased input power density (>2.5 W cm-2). We provide an extensive experimental study of pulse excitations in different thermodynamic regimes for freestanding CNTSs with varying thermal inertias (single-walled and multiwalled with varying diameters and numbers of superimposed sheet layers) in vacuum and in air. The acoustical and geometrical parameters providing further enhancement of energy conversion efficiency are discussed.
RESUMO
Soft, flexible, and stretchable electronic devices provide novel integration opportunities for wearable and implantable technologies. Despite the existing efforts to endow electronics with the capability of large deformation, the main technological challenge is still in the absence of suitable materials for the manufacturing of stretchable electronic circuits and devices with active (sensitive) and passive (stable) components. Here, we present a universal material, based on single-walled carbon nanotube (SWCNT) films deposited on a polydimethylsiloxane (PDMS) substrate, which can act as a material being both sensitive and insensitive to strain. The diverse performance of SWCNT/PDMS structures was achieved by two simple dry-transfer fabrication approaches: SWCNT film deposition onto the as-prepared PDMS and on the prestretched PDMS surface. The correlation between applied strain, microstructural evolution, and electro-optical properties is discussed on the basis of both experimental and computational results. The SWCNT/PDMS material with the mechanically tunable performance has a small relative resistance change from 0.05 to 0.07, while being stretched from 10 to 40% (stable electrode applications). A high sensitivity of 20.1 of the SWCNT/PDMS structures at a 100% strain was achieved (strain sensing applications). Our SWCNT/PDMS structures have superior transparency and conductivity compared to the ones reported previously, including the SWCNT/PDMS structures, obtained by wet processes.
RESUMO
We propose a novel, scalable, and simple method for aerosol doping of single-walled carbon nanotube (SWCNT) films. This method is based on aerosolization of a dopant solution (HAuCl4 in ethanol) and time-controlled deposition of uniform aerosol particles on the nanotube film surface. The approach developed allows fine-tuning of the SWCNT work function in the range of 4.45 (for pristine nanotubes) to 5.46 eV, controllably varying the sheet resistance of the films from 79 to 3.2 Ω/â¡ for the SWCNT films with 50% transmittance (at 550 nm). This opens a new avenue for traditional and flexible optoelectronics, both to replace existing indium-tin oxide electrodes and to develop novel applications of the highly conductive transparent films.