Hydrophilic-oleophobic stimuli-responsive materials and surfaces | Posted on:2009-05-14 | Degree:Ph.D | Type:Thesis | University:Purdue University | Candidate:Howarter, John A | Full Text:PDF | GTID:2441390005451338 | Subject:Chemistry | Abstract/Summary: | | Due to their high surface energy, hydrophilic surfaces are susceptible to contamination which is difficult to remove and often ruins the surface. Hydrophilic-oleophobic coatings have a diverse engineering potential including applications as self-cleaning surfaces, extended life anti-fog coatings, and environmental remediation in the selective filtration of oil-in-water mixtures. A successful design model for hydrophilic-oleophobic behavior has been developed using perfluorinated surfactants covalently bound to a surface. Within this design model, a variety of materials have been explored which the surfactants are covalently bound to a substrate; similarly, the surfactants may also be incorporated as a monomer into bulk copolymers.;Surfactant based surfaces exhibited simultaneous hydrophilicity, necessary for anti-fogging, and oleophobicity, necessary for contamination resistance. The combination of these features rendered the surface as self-cleaning. Surfactant based brushes, composed of polyethylene glycol and perfluorinated constituents were grafted on to silica surfaces. The relationship between brush density and stimuli-responsiveness was determined by varying grafting conditions. The resultant surfaces were characterized with respect to chemical composition, brush thickness, and wetting behavior of water and hexadecane. Optimized surfaces exhibited stimuli-responsive behavior such that the surfaces will be wetted by water but not by oil.;Surfactants were incorporated into random copolymers to create self-cleaning polymers which could be easily coated on to surfaces post-synthesis. Acrylic acid, methyl methacrylate, and hydroxyethyl methacrylate were used as comonomers; feed ratio was varied to establish compositional limits of stimuli-responsive behavior. Polymer composition dictated coating durability and self-cleaning performance as determined by water and hexadecane contact angle. The ability of select coatings to mitigate fogging was assessed in two extreme environments: transition from -20°C to humid laboratory environment; exposure to steaming water vapor.;Silica membranes of varying pore size were modified with stimuli-responsive surfactants. Membranes showed the ability to selectively pass water and restrict passage of oil, demonstrating a reusable method of separating oil-in-water emulsions. Selectivity of oil-in-water emulsions and permeate flow rate of each individual fluid were quantified for the surfactant modified membranes. Permeate flow rate was characterized with respect to individual droplets and bulk fluid. | Keywords/Search Tags: | Surfaces, Stimuli-responsive, Hydrophilic-oleophobic | | Related items |
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