Synthesizing thin and ultrathin polymer films by a two-step deposition/polymerization process
Abstract
The role of conjugated polymer materials in emerging electronic, sensor, display, and optical technologies is rapidly expanding. Future application of such polymers greatly depends on the ability to process them into the form of thin films with desired properties. In an effort to overcome the problem of insolubility of conjugated polymers, we demonstrate the possibility of making thin and ultrathin polymer films by an in-situ vacuum deposition/polymerization process. In this process, the monomer deposition and polymerization are separated to give smoother surface. The process is also able to simultaneously pattern the polymer film by selective UV-induced polymerization. Using time-resolved RAIRS, we have performed kinetic studies for both the monomer adsorption and the polymerization reaction. In general, low substrate temperature favors the deposition of amorphous monomer films, while polycrystalline monomer is formed when substrate temperature is raised. The monomer state and the UV light intensity were discovered to be the most important factors that control the rate of polymerization. We have successfully synthesized polystyrene, polyacrylonitrile, poly(styrene-co-acrylonitrile), and polypyrrole films with thickness from 80 nm to 1 μm. However, we were not able to obtain poly(methyl methacrylate) due to a decomposition reaction. The relation between the UV photon energy and the resulting reactions is discussed for the purpose of selecting desired reactions and improving materials properties. The film properties, including surface morphology, film thickness, molecular weight, and conductivity, have been examined by various experimental techniques such as SEM, AFM, ellipsometry, profilometry, GPC, etc. Based on the preliminary data obtained from several polymers, we come to the conclusion that the monomer deposition/polymerization process has the ability to grow high quality insoluble conjugated polymer films on various substrates. Most significantly, this research demonstrates the potential application of the process in the formation and patterning of conjugated polymers for microelectronic and optoelectronic devices.
Degree
Ph.D.
Advisors
Delgass, Purdue University.
Subject Area
Chemical engineering
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