Controlling wettability by using chemistry and topography generation of ultrahydrophilic surfaces
The control of surface properties, especially wetting behavior, is a major issue since many practical applications can be improved by tuning these behaviors. The ways in which topography and chemistry affect wettability have been studied extensively. Although, ultrahydrophobic and ultralyophobic surfaces have been prepared successfully by tailoring surface chemistry and topography, fabrication of stable hydrophilic surfaces has not received a lot of attention or has been complex and problematic. This work focuses on understanding how hydrophilicity is affected by surface chemistry and topography and generating ultrahydrophilic surfaces by utilizing functional polymeric and small molecules. Methyl-terminated reactive silane-containing methoxypoly(ethylene glycol)s (mPEGs) were synthesized and grafted on silica surfaces. Experimental and theoretical evidence reveals that the surfaces generated upon PEGylation possess significantly low hydrophilicity. These surfaces have lower values of contact angles only after hydration. We proved that contact angle values are significantly affected by the length scale of topography. Rough surfaces possessed much higher values of contact angles. In addition, vinyl and ester terminated monolayers were attached covalently on silica surface. Reaction kinetics and surface properties upon hydroxylation were also investigated. Vinyl terminated monolayers were dihydroxylated using osmium tetraoxide solution. Surfaces prepared by using trivinylcholorosilane produced lowest contact angles values after being dihydroxylated using osmium tetraoxide solution. However, the high wettability obtained for these groups diminishes over time due to surface reconstruction and contamination as evidenced from aging analysis. Ultrahydrophilic surfaces were prepared by adsorption casting of hydrolyzed poly(vinylene carbonate) (PVCa), poly(hydroxymethylene) (PHM), onto hydrophilic and hydrophobic surfaces. Aging analysis indicates that these surfaces resist loss of hydrophilicity. The study of adsorption temperature suggests that adsorption is faster at higher temperatures. Moreover, graft polymerization of vinylene carbonate (VCa) and vinyl ethylenecarbonate (VEC) were studied. Thin films of PVCa and PVEC were prepared by thermal and UV polymerization. Reduction of these films generated PHM and polyvinyl ethylene glycol) (PVEG) chains covalently attached to silica substrates.
0490: Organic chemistry