Browsing by Subject "Liquid crystalline polymers"

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Effects of nanoconfinement on structure and properties of side-chain liquid crystalline polymers
(2013-12) Gonzalez Garza, Paola Anaid; Ellison, Christopher J.
Semi-crystalline polymers have shown increased crystalline order and size when confined in multilayered films by coextrusion1. The resulting large crystals lead to dramatic improvements in gas barrier properties. Ordered polymers whose characteristics are between that of the liquid phase and the crystalline phase are known as liquid crystalline polymers. The highly ordered mesogens in liquid crystalline polymers contribute to their exceptional bulk properties. In this research, side-chain liquid crystalline polymers were confined in multilayered films, made by either multilayer coextrusion or spin coating, with a non-liquid crystalline polymer in an attempt to improve the ordering of the liquid crystalline mesogens. The liquid crystalline behavior and morphology was studied to understand the correlation between the confinement size and the properties of the multilayer films. Commercial main chain liquid crystalline polymers and hydrogen bonded liquid crystalline polymers were also explored in this research for their use in multilayer coextrusion.
Structure and properties of nano-confined main chain liquid crystalline polymers
(2015-05) Li, Zhenpeng, Ph. D.; Ellison, Christopher J.; Freeman, Benny; Willson, Grant; Sanchez, Issac; Holliday, Bradley
Main chain liquid crystalline polymers (MCLCPs) possess many interesting properties, including extraordinary gas/water barrier properties, chemical resistance and mechanical strength, all which imparted by the special chain ordering in liquid crystal phases. Hence, MCLCPs are very attractive candidates in a variety of applications (e.g. high performance gas barrier and separation membranes, solar cells and electronic devices, etc.). Previous studies have shown that the structure and thermophysical properties of polymers can be dramatically affected by nano-confinement. However, most of the studies performed in this area are focused on the effect of nano-confinement of conventional amorphous or semi-crystalline polymers. A comprehensive understanding of structure and ordering of nano-confined MCLCPs is still lacking. Nano-confined MCLCPs (e.g. nanoscale MCLCP thin films) have been widely used in organic electronic devices and fuel cells, therefore, a better fundamental understanding of their structure and properties is key for controlling and improving performance in these applications. In this dissertation, various systems (i.e. multilayer coextrusion, spin coating and nano-imprint lithography) were employed to study the effect of nano-confinement on the structure and properties of MCLCPs. High quality MCLCP multilayer films were fabricated through coextrusion, which could be potentially used as high performance gas/water barrier packaging films. Further studies on spin coated single layer films have shown that the nano-confined MCLCP chains adopted a highly ordered in-plane structure with their chain axis aligned parallel to the film plane. Such unique chain ordering imparted more than an order of magnitude lower gas permeability when compared to that of the bulk due to the increased tortuosity of the gas molecule diffusion pathway. Furthermore, nanoimprint lithography was performed to simultaneously control the chain structure and alignment by nano-confinement and the squeeze flow present during processing.