P‐92: Orientational Ordering of Nematic Liquid Crystal Aligned with a Directly Spinnable Carbon Nanotube Web

Abstract

We studied about the orientational ordering of liquid crystal (LC) aligned with a carbon-nanotube (CNT) web and its temperature dependence. The CNT web works as an alignment layer as well as an electrode. The LC molecules were aligned along the drawing direction of the CNT web but the order parameter S of the unrubbed CNT web sample was lower than the polyimide (PI) sample. To improve S of the CNT web sample, we directly rubbed the CNT web. S of the rubbed CNT web sample was nearly same with the PI sample and also showed similar temperature dependence. We also measured voltage-transmittance curve and the residual dc of the CNT web sample. The CNT web sample showed a good electrooptical modulation of the retardation and smaller residual dc than the PI sample. Author KeywordsCNT web; alignment; nematic liquid crystal Objectives and BackgroundThe liquid crystal (LC) alignment technology has been actively developed for the last decades such as the conventional rubbing method, the ion beam irradiation, and the photoalignment. In recent years, the approaches using a small amount of nanoparticles doped into LC or a polyimide (PI) have drawn a great deal of attention [1][2][3][4][5]. For instance, Kuo et al. reported a vertical alignment of LC using the polyhedral oligomeric silsequioxane (POSS) nanoparticles [1]. Lee et al. showed that a mixture of small amount of multi-wall carbon-nanotube (CNT) and PI induced a uniform surface topography and a faster relaxation of LC molecules [2]. Russell et al. obtained a planar alignment using the film of aligned CNT bundles deposited on glass [3]. Furthermore, Fu et al. [4] and Jiang et al. [5] found that aligned CNTs could function both as the alignment layer and electrode. However, in the previous paper [5], the orientational ordering of LC and the temperature dependence of LC ordering was not studied.In this report, we studied about the orientational ordering of LC aligned with CNT web and its temperature dependence. The LC molecules were aligned along the drawing direction of the CNT web. The order parameter S of the rubbed CNT web sample was nearly same to the rubbed PI sample. We also measured voltagetransmittance and the residual dc properties. The rubbed CNT sample showed smaller residual dc than the PI sample. MethodsDirectly spinnable CNTs (dsCNTs) were grown on silicon wafers. The wafers were annealed in a 90 mm inner diameter quartz tube reactor at 680 o C under helium (4000 sccm, 40 min). Acetylene (100 sccm) and hydrogen (100 sccm) were added to the flow and the reaction run for 20 min to give ~400 μm long CNTs of 10 nm diameter. A web of dsCNTs was drawn from the front face of the dsCNTs forest and laid onto a glass substrate [6].To fabricate the PI sample, a commercial PI SE7492 (Nissan) was coated onto an indium-tin-oxide (ITO)-deposited glass substrate and then baked at 200 o C for 1 h. The substrates were rubbed with a cotton cloth and assembled in an antiparallel fashion. For the measurement of S, the cell gap d was fixed at 3.2 μm using bead spacers. ...

Flexible and Thermally Stable Optical Polarizers Based on Highly Aligned Carbon Nanotube Sheets for the Visible Spectral Range

“…In recent years, a technique for spinning a carbon nanotube (CNT) sheet with the CNTs aligned in one direction from a vertically grown CNT forest has been introduced . Thus, various devices, such as touch screens, electrodes, polarizers, and speakers based on CNT sheets have been reported . In particular, since CNTs are excellent optoelectronic materials with broadband anisotropic light‐absorption properties, highly aligned CNT sheets are very promising for developing WGP films.…”