Carbon nanotubes in liquid crystals as versatile functional materials

Abstract

Liquid crystals can be easily aligned in desired directions by treated surfaces or by external fields. The least ordered liquid crystal phase, the nematic, exhibits orientational order that can be easily transferred onto carbon nanotubes dispersed in it. The alignment of the carbon nanotubes can be demonstrated by polarized Raman spectroscopy. Carbon nanotubes not only well integrate in the matrix but also, even at very low concentration, have a detectable effect on the liquid crystal properties that can be very attractive for display applications. The presence of big aggregates of carbon nanotubes, on the other hand, interfere strongly with the switching behaviour of the liquid crystal, as we can show following the local switching of liquid crystal molecules with Raman spectroscopy.

Carbon nanotubes in liquid crystals

“…The large polarisation dependence of the intensities of both peaks shows that the CNTs and LC are aligned equally. 60 Recently, the polarised Raman technique was employed also to track the electric-field-induced switching of the LC in the vicinity of a SWCNT aggregate that was much too large to allow LC-alignment of the contained nanotubes 21 . 22,23 : some studies report no improvement (often even a deterioration was observed), others report enhancement in some respects while degradation was observed in other parameters (which however were reported to be improved in yet other studies).…”

Carbon Nanotubes in Liquid Crystals

“…The large polarisation dependence of the intensities of both peaks shows that the CNTs and LC are aligned equally. 60 Recently, the polarised Raman technique was employed also to track the electric-field-induced switching of the LC in the vicinity of a SWCNT aggregate that was much too large to allow LC-alignment of the contained nanotubes 21 . In that case the CNTs influenced the director, rather than the other way 65 around, stabilizing the starting configuration and counteracting the effect of the electric field.…”

“…a display. Reported effects include reduced effective ion content 16,18,20,21 , increased dielectric anisotropy 16,17,19 , suppressed backflow effects 16,17 , faster 10 electrooptic response due to reduced rotational viscosity 14 and lower switching threshold 16,17,19 . The CNT concentration was in all these works kept extremely low, yet substantial effects were reported.…”

“…via polymerization) to produce a composite material with enhanced macroscopic mechanical, electronic and / or thermal properties, or it can be removed, a 55 necessary step in the development of most CNT-based devices, which are generally incompatible with the LC matrix. A number of reports have appeared recently suggesting a beneficial CNT-LC relationship also in the other direction, the LC behavior in electrooptic devices such as displays possibly being improved by the presence of small amounts of CNTs 21 . Although clearly an appealing concept, we will in this review only briefly touch upon this issue, as the observations are far from understood and have also been challenged by contradictory reports 22,23 .…”

Dispositivos de cristal líquido dopados con nanopartículas = Nanoparticle-doped liquid crystal devices

“…Se sabe que los CNTs presentan distinta intensidad Raman dependiendo de la polarización de la luz que se aplica y si ésta incide paralela o perpendicular al eje largo. De este modo se ha podido detectar en CL nemáticos positivos dopados con CNTs, que éstos siguen al CL cuando se reorienta [140,141]. Mediante el mismo método se ha estudiado la relación de anclaje entre CNTs y CL, y si la composición de las moléculas de CL tiene algún efecto en este proceso [142].…”