Browsing by Author "Sylvester, SO"

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    Nanoscale condensation of water on self-assembled monolayers
    (Royal Society of Chemistry, 2011-06-07) James, M; Darwish, TA; Ciampi, S; Sylvester, SO; Zhang, Z; Ng, A; Gooding, JJ; Hanley, TL
    We demonstrate that water is almost universally present on apparently dry self-assembled monolayers, even on those considered almost hydrophobic by conventional methods such as water contact goniometry. The structure and kinetics of nanoscale water adsorption onto these surfaces were investigated using X-ray and neutron reflectometry, as well as atomic force microscopy. Condensation of water on hydrophilic surfaces under ambient conditions formed a dense sub-nanometre surface layer; the thickness of which increased with exponentially limiting kinetics. Tapping mode AFM measurements show the presence of nanosized droplets that covered a small percentage ([similar]2%) of the total surface area, and which became fewer in number and larger in size with time. While low vacuum pressures ([similar]10-8 bar) at room temperature did nothing to remove the adsorbed water from these monolayers, heating to temperatures above 65 [degree]C under atmospheric conditions did lead to evaporation from the surface. We demonstrate that water contact angle measurements are not necessarily sensitive to the presence of nanoscale adsorbed water and do not vary with time. For the most part they are a poor indicator of the kinetics and the amount of water condensation onto these surfaces at the molecular level. In summary, this study reveals the need to exclude air containing even trace amounts of water vapor from such surfaces when characterizing using techniques such as X-ray reflectometry.© 2011, Royal Society of Chemistry
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    Nanoscale water condensation on click-functionalized self-assembled monolayers
    (American Chemical Society, 2011-09-06) James, M; Ciampi, S; Darwish, TA; Hanley, TL; Sylvester, SO; Gooding, JJ
    We have examined the nanoscale adsorption of molecular water under ambient conditions onto a series of well-characterized functionalized surfaces produced by Cu(I)-catalyzed alkyne–azide cycloaddition (CuAAC or “click†) reactions on alkyne-terminated self-assembled monolayers on silicon. Water contact angle (CA) measurements reveal a range of macroscopic hydrophilicity that does not correlate with the tendency of these surfaces to adsorb water at the molecular level. X-ray reflectometry has been used to follow the kinetics of water adsorption on these “click†-functionalized surfaces, and also shows that dense continuous molecular water layers are formed over 30 h. For example, a highly hydrophilic surface, functionalized by an oligo(ethylene glycol) moiety (with a CA = 34°) showed 2.9 Ã… of adsorbed water after 30 h, while the almost hydrophobic underlying alkyne-terminated monolayer (CA = 84°) showed 5.6 Ã… of adsorbed water over the same period. While this study highlights the capacity of X-ray reflectometry to study the structure of adsorbed water on these surfaces, it should also serve as a warning for those intending to characterize self-assembled monolayers and functionalized surfaces to avoid contamination by even trace amounts of water vapor. Moreover, contact angle measurements alone cannot be relied upon to predict the likely degree of moisture uptake on such surfaces.© 2011, American Chemical Society