Transparent Film Heater Using Single‐Walled Carbon Nanotubes

Abstract

Since their discovery, many practical applications of carbon nanotubes (CNTs) have been proposed because of their excellent properties. Many researchers have reported remarkable electrical, optical, and thermal properties of CNTs. The electrical conductivity of single-walled carbon nanotubes (SWCNTs) is very high (10 6 S m -2 ). Films made of SWCNTs also possess a low sheet resistance and exhibit an optical transmittance in the visible spectrum comparable to that of commercial indium tin oxide (ITO). [1,2] Recently, a thermal conductivity of nearly 3500 W m -1 K -1 was measured at room temperature for SWCNTs measuring 2.6 lm in length and 1.7 nm in diameter. [3] This thermal conductivity value is much higher than that of diamond. In the field of thermal engineering, research has focused on enhancing their heat-transfer properties. CNTs have been modeled as heat-sink fins in cooling channels for microelectronics, and several groups have developed various CNT mats and composites for the next generation of thermal interface materials. [4][5][6][7][8][9][10][11][12][13] Although a high thermal conductivity is a central issue in thermal engineering, few pioneering works have utilized other useful properties of CNTs, such as their high electrical conductivity and optical transparency. Therefore, we propose a unique application of SWCNT films as transparent heaters. Currently, thin ITO films has been used as transparent heaters in various applications, such as outdoor panel displays, avionic displays, liquid-crystal display (LCD) panels for use in harsh environments, periscopes, and vehicle window defrosters. However, ITO film heaters have some limitations, such as a slow thermal response and complex fabrication processes.Because CNT films have a high thermal conductivity and can be produced by using various common fabrication methods [1,2,[14][15][16] they are a promising alternative to ITO films in transparent heaters. To our knowledge, there are no reports about transparent CNT film heaters. Therefore, we fabricated the first transparent film heater using SWCNTs and investigated its heating performance. Purified SWCNTs were grown by using the arc discharge technique. We chose the vacuum filtration method to fabricate the transparent SWCNT films. In this manner we could control the transparency and obtain excellent uniformity of the networked SWCNT films.[2] First, the SWCNT samples were purified using standard processes, such as centrifugation, acid treatment, and membrane filtration. The SWCNTs were then dispersed in deionized water with a 1 wt % sodium dodecyl sulfate (SDS) solution and sonicated for several hours. The film transparency was modulated by adjusting the volume of the SWCNT solution between 0.5 and 4.0 mL. This resulted in SWCNT films with a transparency of 65-97 % and a sheet resistance of 230-3500 X m -2 . An anodic aluminium oxide (AAO) membrane with 200 nm pores (Whatman International, Anodisc 47) was used as a filter. The CNT membrane was soaked in NaOH solution for 1 h, rinsed with deionized wate...

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