Wednesday, November 11, 2015: 10:10 AM
155F (Salt Palace Convention Center)
Several modification methods have been used for surface nanostructuring of polyamide surfaces in order to increase surface hydrophilicity (i.e. decrease protein/bacteria fouling propensity), including physical modification (i.e. embedding nanoparticles, coating, etc.), chemical modification, UV or gamma irradiation, or plasma activation. In the present work, hydrophilic polymer chains were graft polymerized onto the surface of polyamide (PA) membrane via atmospheric pressure plasma-induced graft polymerization (APPIGP). The resulting polymeric brush layer lowers the free energy of hydration to a level suitable for reducing surface fouling. Prior to graft polymerization, the PA Surface is activated via atmospheric pressure plasma treatment to form free-radical peroxy initiation sites. The surface density of active sites depends on the type of plasma gas as illustrated in the study for helium and hydrogen plasma, plasma exposure time, and plasma power. Subsequently, graft polymerization was accomplished using an aqueous vinyl monomer solution resulting in a "brush" polymeric layer of chains that are terminally and covalently bonded to the polyamide surface. The rate of graft polymerization and thus the resulting chain size is affected by the initial monomer concentration, reaction temperature and time, and polymerization control agents. In the present work, the monomers acrylic acid, 2-hydroxyethyl methacrylate, and vinylsulfonic acid were selected to form surface brush layers of poly(acrylic acid) (PAA), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(vinylsulfonic acid) (PVSA). Surface topography was quantified in terms of feature height distribution determined by atomic force microscopy (AFM). Surface hydrophilicity/hydrophobicity was assessed via contact angle measurements with different solvents to determine the polar and dispersive components of the surface energy. It is shown that both surface roughness and free energy of hydration (i.e., wettability) can be tailored through the selected vinyl monomer chemistry, surface plasma exposure, and polymerization conditions. Studies on fouling resistance with model foulants correlated with surface hydrophilicity and topography thereby allowing tailor-design of fouling-resistant membrane surfaces for challenging water desalination applications.