Nanophase Separation and Photochemical Reaction of Rodcoil Molecules, Reactive Liquid Crystal Molecules, and Binary Mixtures
Gresham, Kyle Daniel
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https://hdl.handle.net/2142/82899
Description
Title
Nanophase Separation and Photochemical Reaction of Rodcoil Molecules, Reactive Liquid Crystal Molecules, and Binary Mixtures
Author(s)
Gresham, Kyle Daniel
Issue Date
1998
Doctoral Committee Chair(s)
Stupp, Samuel I.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
"This work presents the synthesis and characterization of three related organic systems designed for self-assembly into ordered materials such as two dimensional objects and nanostructures. A family of reactive block molecules referred to as ""rodcoils"" was synthesized for the purpose of forming nanostructures. In these reactive rodcoil molecules rod-like segments are covalently attached to less rigid coil-like segments. These rodcoil molecules were found to assemble into extremely small aggregates of dimensions on the order of 2-3 nm. New reactive thermotropic liquid crystalline compounds with structure similar to the rod segments of the rodcoil molecules were synthesized and their mesophase behavior characterized. These compounds contained photochemically sensitized groups such as anthracene and diacetylene segments. Irradiation of these materials at various temperatures led to the formation of distinct dimesogens and other high molecular weight material which allowed one of the reactive liquid crystals to act as a negative photoresist for the lithographic formation of 3-5$\mu$m features on a silicon wafer. A new methodology for the formation of nanostructures that is presented for the first time in this work is the use of binary mixtures of rodcoil molecules and chemically similar rod molecules. This system was found to form two different types of nanomorphology seen by TEM. The first was a kinetically trapped, striped nanomorphology that was still reactive to topochemical reaction of the rods and which disappeared upon heating to 120$\sp\circ$C. Secondly, nanocrystals, with dimensions of 3-10 nm were found in the striped regions of as-cast films believed to contain mostly rodcoil molecules. These nanocrystals became more prevalent throughout the film upon heating to 100$\sp\circ$C whereas the striped morphology disappeared. At 120$\sp\circ$C, the nanocrystals also melt to form a new mixed phase exhibiting characteristic X-ray and electron diffraction patterns. Interestingly, the size and shape of the nanocrystals was constant upon heating which is in contrast to what would be expected of classic nucleation and growth behavior. This is thought to be due to interactions of the rodcoils and rods which limits the size of the aggregates and allows for the formation of a more thermodynamically stable phase containing nanocrystals surrounded by a less ordered matrix."
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