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Issue 11, 2011
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Nanoscale condensation of water on self-assembled monolayers

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Abstract

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 (∼2%) of the total surface area, and which became fewer in number and larger in size with time. While low vacuum pressures (∼10−8 bar) at room temperature did nothing to remove the adsorbed water from these monolayers, heating to temperatures above 65 °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.

Graphical abstract: Nanoscale condensation of water on self-assembled monolayers

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Publication details

The article was received on 18 Jan 2011, accepted on 22 Mar 2011 and first published on 18 Apr 2011


Article type: Paper
DOI: 10.1039/C1SM05096F
Soft Matter, 2011,7, 5309-5318

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    Nanoscale condensation of water on self-assembled monolayers

    M. James, T. A. Darwish, S. Ciampi, S. O. Sylvester, Z. Zhang, A. Ng, J. J. Gooding and T. L. Hanley, Soft Matter, 2011, 7, 5309
    DOI: 10.1039/C1SM05096F

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