Computer Simulations of Faceted Nanoparticles and Carbon Nanotubes in Liquid Crystals

• Main Author: Bale, Shivkumar Shankar
• Other Authors: Chen, Bin
• Format: Others
• Language: en
• Published: LSU 2012
• Subjects: Chemical Engineering
• Online Access: http://etd.lsu.edu/docs/available/etd-07052012-234402/

The purpose of this research is to investigate the use of liquid crystals (LCs) to manipulate and organize faceted nanoparticles and carbon nanotubes (CNTs). Computer simulations at different levels of detail are used to study these systems. Results from this project will be relevant for potential applications of these systems in displays, nanoscale electronics, electro-optical switches, and in the development of composites with unique mechanical, thermal and/or electronic properties. In this research, two independent but directly related projects were carried out. In the first part of the research, we investigated the torque that develops when faceted nanoparticles, namely cubes and triangular prisms, are immersed in a nematic LC. We used a mesoscale theory in terms of the tensor order parameter Q(r) to model the nematic. Homeotropic anchoring condition of the NLC is imposed on the surfaces of faceted nanoparticles. Our results indicate that, when the particle is oriented at an out-of-plane orientation (i.e. unstable configuration), it moves away immediately from that state and then slowly orients itself back to the stable configuration (i.e. in-plane orientation). The magnitude of the out-of-plane torques is similar to that of in-plane torques. In case of an isolated nanoprism system, the torque reaches maximum when the particle orients with one of its rectangular sides parallel to the far field director n(r). In contrast, the torque of an isolated nanocube system reaches maximum when the particle orients with its four lateral faces parallel to the far field director n(r). In the second part of our research, we investigated the effect of varying the molecular structure and the phase of the LC on the CNTs interactions by performing MD simulations. Our results suggest that increasing the chain length of the hydrophobic tail of the nCB LC molecule decreases the tendency of aggregation for CNTs in nCB LCs. Additionally, varying the phase of the nCB LC is insufficient to decrease the tendency of aggregation for CNTs.