Thesis (Ph. D.)--University of Rochester. Dept. of Mechanical Engineering, 2009.
New techniques to fabricate structured polymer films using chemical
vapor deposition were developed and studied. Two different vapor deposition
approaches, one using step-growth polymerization and another using
chain-growth polymerization, were employed. The primary objective of this thesis
was to determine the feasibility of controlling morphology of vapor-deposited
polymer films by introducing non-reactive, immiscible components into the vapor
deposition process. Poly(amic acid)s, condensation polymers and precursors to rigid-rod
polybenzoxazoles (PBO), formed upon co-deposition of 3, 3’-dihydroxybenzidine
(DHB) and pyromellitic dianhydride (PMDA). Deposited coatings were cured
under inert gas conditions and resulted in the conversion to semi-aromatic
polybenzoxazoles at around 550 °C. Physical and chemical changes occurring
during the curing process were studied with FT-IR, TGA and nanoindentation
experiments. Successful fabrication of PBO films provided a platform to study
simultaneous film growth and phase separation in vapor-deposited condensation
polymers. Control of morphology of vapor-deposited condensation polymer films
was achieved by the fabrication of polyimide/CuPc composite films, which were
made from the co-evaporation of 4,4’-oxydianiline (ODA) and 3,3’,4,4’-biphenyl
tetracarboxylic dianhydride (BPDA) in the presence of non-reactive, third-component
CuPc. Spectroscopy experiments confirm the formation of polyimide segments and
suggest that embedded CuPc molecules have less mobility compared to pure CuPc
films. Electron microscopy and XRD studies show evidence of embedded CuPc particles at the surface and in the bulk of fine lateral structure with a length scale
of about 100 nm.
Fabrication of poly (methyl methacrylate) (PMMA) films using initiated
chemical vapor deposition (iCVD) provided a platform to investigate film growth and
phase separation for a classical chain-growth polymer. An axisymmetric,
multi-component iCVD apparatus was designed to study the vapor-phase growth of
glassy PMMA films. Key reactor operating parameters, including the hot-zone
temperature, reactor base-pressure, substrate temperature, and the monomer/initiator
molar feed ratio were systematically varied to understand film growth kinetics. The
non-reactive solvent-vapor, t-butanol, was then introduced into the deposition process
to promote polymer film dewetting. When solvent-vapor is used, non-equilibrium
dewetted structures comprising of randomly distributed polymer droplets were
observed. The length-scale of observed topographies, determined using power
spectral density (PSD) analysis, ranges from 5 to 100 microns and can be
influenced by deposition conditions, especially the carrier gas and solvent-vapor
flowrates. Control over lateral length-scale is demonstrated by preparation of
hierarchal “bump-on-bump” topographies. Autophobic dewetting of PMMA from
SiOx/Si substrate during iCVD process is attributed to a thin film instability driven
by both long range van der Waals forces and short range polar interactions.
