Effect of carbon nanotubes on phase transitions of nematic liquid crystals |
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Authors: | Hatice Duran Bruce Gazdecki Atsushi Yamashita Thein Kyu |
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Affiliation: | a Department of Polymer Engineering, The University of Akron, Akron, OH 44325-0301 |
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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. |
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