title: Three-Dimensional pH Mapping within Model Hybrid Xerogel Thin Films.
abstract: When xerogel films derived from carboxyethylsilanetriol (COE) and tetraethoxysilane (TEOS) or 3-aminopropyltriethoxysilane (APTES), n-octyltriethoxysilane (C8), and TEOS are formed on Al2O3they exhibit chemically segregated domains with unique chemistries and topographies. These characteristics are important for marine antifouling. By using the ratiometric fluorescent probe 5 (and 6)-carboxy SNARF-1 (C.SNARF-1) in concert with confocal fluorescence microscopy, we determine the pH in three dimensions within these hybrid films. For the COE/TEOS film, 4-5 μm diameter dendritically shaped features form, and they extend ∼100 nm above the film base. These dendritic features are acidic (pH < 7) in comparison to the film base. Their average diameter decreases as we progress from the solution-film interface toward the film-Al2O3interface. Planes located at the solution-film interface, film center, and film-Al2O3interface exhibit acidic surface areas that are 20% below, 50% above, and 70% below the average COE mole fraction used to create the film. In the APTES/C8/TEOS films, 1-3 μm diameter mesa-shaped features form, and they extend up to 450 nm above the film base. These mesa features are basic (pH > 7) in comparison to the film base and are columnar in shape, extending without change in diameter throughout the entire film. From the solution-film interface the planes located within the first 3/4 of the film exhibit basic surface areas that are equivalent to the average APTES mole fraction used to create the film. However, as one approaches the film-Al2O3interface, many new 100-200 nm basic subsurface regions appear. The basic surface area in those film planes within 400-500 nm of the film-Al2O3interface are enriched in APTES by up to 500% above the average APTES mole fraction used to create the film.
authors.affiliation: Department of Chemistry, Natural Sciences Complex, University at Buffalo, The State University of New York , Buffalo, New York 14260-3000, United States.
authors.forename: Joel F
authors.initials: JF
authors.lastname: Destino
authors.affiliation: Department of Chemistry, Natural Sciences Complex, University at Buffalo, The State University of New York , Buffalo, New York 14260-3000, United States.
authors.forename: Andrew K
authors.identifier: 0000-0003-2599-2918
authors.initials: AK
authors.lastname: Craft
authors.affiliation: Department of Chemistry, Natural Sciences Complex, University at Buffalo, The State University of New York , Buffalo, New York 14260-3000, United States.
authors.forename: Frank V
authors.identifier: 0000-0002-1500-5969
authors.initials: FV
authors.lastname: Bright