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

Abstract

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.