Study on Carbon Nanotube Doped Nematic Liquid Crystals

• Main Authors: Yu-ChiaHuang, 黃裕家
• Other Authors: Andy Ying-Guey Fuh
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/17196703809319911213

博士 === 國立成功大學 === 光電科學與工程學系 === 101 === This dissertation is dedicated to the study on the binary mixture of nematic liquid crystal (NLC) and carbon nanotube (CNT). Based on the literatures over the decade, this novel combination exhibits eye-catching characteristics such as mutual alignment, guest-host effect under electric fields, improved non-linear optic properties and electro-optical performances etc. Thus, besides a brief introduction to both materials, this dissertation starts from a scientific review on the historic studies related to this novel mixture. After the background and the review chapters, presented is the characterization of the physical properties of the mixture through thermal, optical, dielectric measurements and computer calculations, re-assuring the enhancements of dielectric anisotropy, birefringence, rotational viscosity and effective elastic coefficient of the mixture, yet the decrease in the phase transition temperature compared with the pristine NLC matrix. Although the combination seems attractive and promising, it is ill-famed and observed in our experiments that the agglomeration of CNTs in LCs is serious and dissolving these two components into a reliable and empirically repeatable mixture is indeed, a painstaking and frustrating task. Therefore, a theoretical study which is based upon the well-known, yet for the first time (to the best of our knowledge), Flory-Huggins model is applied in effort to solubilization of the polar LCs and the non-polar CNTs. The results reveal that when the grafting ratio of maleic anhydride (MA) functionalized single-walled CNT (SWCNT-MA) is 20 atomic weight percent, SWCNT-MA can dissolve in the 5CB liquid crystal solvent within certain length and composition range. And when the grafting ratio reaches up to 30 atomic weight percent, SWCNT-MA can spontaneously and fully dissolve in the NLC with all regular CNT lengths and mixture compositions. On the other hand, to interpret the physical phenomena observed in our experiments, especially for the enhanced dielectric anisotropy which is an important factor for the binary mixture to play a role in future applications, a numerical analysis using the Maxwell Garnett approximation method was performed , and the results show that the Debye parameter of the CNT dopant at optic frequency limit seems to be the key physical cause of the enhancement of dielectric anisotropy of the NLC host.