Effect of carbon nanotubes on phase transitions of nematic liquid crystals

Abstract

Phase diagrams of multi‐wall carbon nanotube (MWNT)/nematic liquid crystal (E7) and buckminsterfullerene (C60‐I h)/nematic liquid crystal (E7) binary systems have been investigated by means of polarizing optical microscopy and differential scanning calorimetry. It was found that the isotropic–nematic phase transition temperature (T NI) of the liquid crystal component was enhanced by the incorporation of MWNT within a small composition gap. A chimney‐type phase diagram can be identified in the MWNT/E7 mixture over a narrow range of ∼0.1–0.2% MWNT concentration. Upon substituting the nanotubes with isotropic fillers such as fullerene, the (C60‐I h)/E7 blend showed no discernible change of T NI in the same concentration range of the chimney of the MWNT/E7 mixture, suggesting a significant contribution of anisotropy (or the aspect ratio) of the nanotubes to the entropy of the system containing liquid crystal molecules. This enhanced T NI phenomenon may be attributed to anisotropic alignment of liquid crystal molecules along the carbon nanotube bundles.