Browsing by Subject "Liquid Crystal"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Synthesis and Characterization of Polymer Composites Containing Aligned Conducting Polymers and Carbon Nanotubes(2014-04-21) Manda, SwathiMiniaturization of electronics and impending demand for bendable electronic gadgets creates a dire need for a thin and flexible film technology that would not only provide spot cooling for the crammed transistors, but also tap into the waste heat generated to produce a portable power source. Thin film thermoelectrics offer a viable solution and have several structural, chemical and economical advantages over inorganic thermoelectric materials. However, their low power factor compared to that of inorganic materials prevents them from being used for practical applications. The tradeoff between Seebeck coefficient and electrical conductivity restricts the improvement of power factor through increase in number of charge carriers. However, controlled modulation of the mobility of charge carriers has a potential to increase the electrical conductivity without adversely affecting the Seebeck coefficient. This research involves investigating a novel way to fabricate organic thermoelectric thin films with high power factor by modulating the morphology of the conducting polymer poly-(3,4-ethylenedioxythiophene) (PEDOT) and creating a composite with carbon nanotubes to control the mobility and hence the electrical conductivity of the thin films. Aligned PEDOT-carbon nanotube composite thin films were fabricated and characterized to study both the alignment of the polymer chains and change in their electrical conductivity. This research utilized the bottom up self organized molecular system templates to control the nano structure and ordering of the polymer?carbon nanotube composite. Liquid crystal template was used to capture all the monomer (3,4-ethylenedioxythiophene) EDOT molecules within the cylindrical cores of hexagonal mesophase oriented in effective net direction within domains, and the monomers were electro-polymerized to obtain aligned polymer chains. This aligned structure renders better anisotropic electrical conductivity along the polymer chain direction. A non percolated dispersion of carbon nanotubes and dopants was incorporated into the aligned PEDOT thin film by spraying as well as internally dispersing within the liquid crystal network before polymerization. The carbon nanotube and dopant incorporation into the aligned PEDOT thin films increased the electrical conductivity by about two orders of magnitude.Item Synthesis and Liquid Crystal Phase Transitions of Zirconium Phosphate Disks(2013-05-07) Shuai, MinSolvent-mediated self-assembly of nanoparticles is an effective and efficient way for the bottom-up organization of functional structures. The primary object of this work is to build up a model system for the study of suspensions of disk-shaped nanoparticles, and use it for the study of self-assembly and discotic liquid crystal phase transitions of discotic particles. The work was introduced by the control over the size and polydispersity of zirconium phosphate (ZrP) disks through synthesis. Systematic experiments revealed that regular-shaped ?-zirconium phosphate crystalline disks with a size-to-thickness ratio from 1 to 50 and size polydispersity as low as 0.2 can be obtained through hydrothermal treatment in 3 M to 15 M phosphoric acid solutions. Transmission and scanning electron micrographs revealed that the growth of the disks is mediated by oriented attachment, which happened continuously throughout the hydrothermal treatment between various sized disks. Ostwald ripening is effective in improving the regularity of the shape of the disks, especially under prolonged hydrothermal treatment. Under the microwave assisted hydrothermal conditions, the rate of attachment on the flat surfaces of the disks is accelerated, which leads to the formation of the column-shaped crystals. With the ability to adjust the size, aspect ratio, and polydispersity of ZrP disks, the study on self-assembly behavior and the discotic liquid crystal phases was enabled. Firstly, liquid crystal phases of aqueous suspensions of ZrP disks were investigated. Iridescent smectic phase and the critical points of phase transitions were found. Moreover, monolayer ZrP nanosheets with extremely high aspect ratio, which were achieved by exfoliating the ZrP crystals, were also used in this study. The high aspect ratio of nanosheets produces a laminar phase at low nanosheet concentration. Chiral liquid crystal phases were demonstrated when increased the concentration of the nanosheets. The competition between the chirality and layering leads to twisted and layered structures. For the final part, solvent-mediated self-assembly of disks and nanosheets via undulation of liquid crystal phases showed an interesting approach for bottom-up design of functional nano-structures.