Title: Carbon nanotube concentration effects on the elelctro-optic properties of liquid crystals

Abstract

The major objective of this study wastoimprove the quality of liquid crystal devices by using carbon nanotubes. The concentration of inserted particles is crucial for the electro-optic properties and doesn’t present a continuous behavior suggesting a bundling process after a critical value (about 0.5% mass fraction of MWCNT). This paper is aimed to qualitatively explain the electro-optic behavior of nematicliquid crystals with carbon nantubes dispersions at different temperatures in the nematic range for low concentration (below 0.5%massfraction) and for high concentration(above 0.5 mass fraction). The analyzed samples were prepared by mixing 7CB nematic with multiwalled carbon nanotubes. The nanotube’s length is between 0.1 to 10 micrometers, the inner diameter is 2 nm – 6 nm and the outer one is about 10 nm to 15 nm. The samples were mixed in two concentrations 0.36% and 1.3% (mass fraction) and used to fill 15 micrometers thick planar aligned cell. To determine the electric Freedericksz transition threshold, a laser beam was sent through the sample subjected toan external electric field. The emergent beam intensity was recorded and plotted versus the applied field. The Freedericksz transition decreases with the CNT adding if the concentration is lowand increases for high concentration when compared to simple 7CB samples. This suggests a bundling phenomenon occurs in high concentration and theinteractions with the host molecules and the applied field is different. The most important aspect observed is a decrease of the Freedericksz transition threshold when small amounts of MWCNT are added. For high nanoparticles concentration, the transition threshold is increased due to the bundling effects.