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Wettability of polymer surfaces: Effects of chemistry and topography
Various methods for modification of polymer surfaces were studied with the objective of controlling changes in wetting behavior. Random copolymers and block copolymers were synthesized by free radical polymerization and atom transfer radical polymerization, respectively, of methacryloxymethyl- or methacryloxypropyltiis(trimethylsiloxy)silane and methyl methacrylate. These polymers spontaneously rearrange to concentrate the low energy, non-wettable siloxane at the surface. The nanoporous nature of the surfaces of these polymers was confirmed using X-ray photoelectron spectroscopy (XPS) analysis and dynamic contact angle analysis. Another method for wettability modification that was studied was the selective modification of polymer surfaces using 3-aminopropyltriethoxysilane (APTES); this provided surfaces with silica-like reactivity. This surface chemistry had been reported for poly(ethylene terephthalate); this thesis work expands the reaction to many other polymers (ostensibly all that are H-bond acceptors). Variations in temperature, concentration, and solvent were studied as well as reagent mixtures with tetraethoxysilane. Our experiments led us to propose a new pathway for the reaction. Subsequently, polymers were hydrophobized by fluorination with a monochlorosilane. ^ Argon plasma sputtering of polymers was investigated and a new mechanistic scheme was developed for non-classical polymer sputtering in which the polymer depolymerizes yielding gas-phase monomer which then re-polymerizes. This new understanding of the sputtering process was used to create ultrahydrophobic surfaces, which water drops were unstable on. Polymer surfaces were simultaneously roughened and hydrophobized to test the effect of roughness and topography on surface wettability. A new phenomenological model for wettability was developed with this knowledge in which wettability is treated as a one-dimensional contact line issue. For droplet motion to occur, an energy barrier to three phase contact line motion must be overcome, which can be accomplished by: (1) surface structures becoming smaller to lower barriers to motion and/or (2) contortion of the contact line to raise its ground state energy. ^
Jeffrey P Youngblood,
"Wettability of polymer surfaces: Effects of chemistry and topography"
(January 1, 2001).
Doctoral Dissertations Available from Proquest.