Spontaneous Polymer Thin Film Assembly and Organization Using Mutually Immiscible Side Chains

Polymer ultrathin film self-assembly and organization on
solid substrates has been directed using grafted
siloxane copolymers bearing mutually immiscible alkyl and
perfluoroalkyl side chains. Polysiloxanes grafted
with
both alkyl disulfide and perfluoroalkyl side chains have been
synthesized and characterized. These terpolymer
systems
assemble spontaneously on gold surfaces, forming bound polymeric
monolayers organized by intramolecular phase
separation. Interfacially bound polymer monolayer fabrication is
driven by multipoint alkyl disulfide side chain
chemisorption to gold surfaces from dilute organic solution.
Immiscible perfluoroalkyl side chains of low
interfacial
energy enrich the ambient-exposed outer regions of these monolayers,
yielding a novel bound polymer monolayer
with an anisotropic, layered structure and perfluorinated surface
properties. Ellipsometry indicates that these polymer
films have thicknesses ranging from 22 to 32 Å, depending on solution
conditions and chemistry. Angular-dependent
X-ray photoelectron spectroscopy has provided a depth profile of the
bound polymer films, detailing the anisotropic
composition resulting from perfluoroalkyl surface enrichment.
Static secondary ion mass spectrometry measurements
support the enrichment of perfluoroalkyl groups in the outer atomic
levels of these films. Cyclic voltammetry using
the redox probes Fe(CN)63-
and methylviologen with film-coated gold electrodes evaluated
film-attenuated electron
transfer. Time-of-flight secondary ion mass spectrometry has been
used to image micropatterned polymer surfaces
lithographed at high resolution both before and after organic monolayer
assembly. Qualitative and quantitative
information on film spatial organization and surface chemistry
distribution on microstructures was obtained.