Browsing by Author "Craig, VSJ"

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    Direct measurement of van der waals and diffuse double-layer forces between titanium dioxide surfaces produced by atomic layer deposition
    (American Chemical Society, 2012-04-12) Walsh, RB; Nelson, A; Skinner, WM; Parsons, DF; Craig, VSJ
    The van der Waals forces between titanium dioxide surfaces produced by atomic layer deposition (ALD) at the isoelectric point have been measured and found to agree with the calculated interaction using Lifshitz theory. It is shown that under the right conditions very smooth ALD surfaces are produced. At pH values slightly below and above the isoelectric point, a repulsive diffuse double-layer repulsion was observed and is attributed to positive and negative charging of the surfaces, respectively. At high pH, it was found that the forces remained repulsive up until contact and no van der Waals attraction or adhesion was evident. The absence of an attraction cannot be explained by the presence of hydration forces.© 2012, American Chemical Society
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    Model surfaces produced by atomic layer deposition
    (Chemical Society of Japan, 2012-10-05) Walsh, RB; Howard, SC; Nelson, A; Skinner, WM; Liu, GM; Craig, VSJ
    Atomic layer deposition is used with the aim of producing new model surfaces suitable for fundamental wet surface science investigations. Alumina surfaces are found to dissolve in aqueous solutions, although they can be passivated against dissolution by adsorption. Highly useful thick titania films can be produced by employing low temperatures during formation, whereas hafnia and zirconia films have a tendency to produce films that crystallize, and this increases the roughness of the films. © 2012, The Chemical Society of Japan.
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    Underscreening in concentrated electrolytes: re-entrant swelling in polyelectrolyte brushes
    (Royal Society of Chemistry, 2023-09-30) Robertson, H; Elliott, GR; Nelson, ARJ; Le Brun, AP; Webber, GB; Prescott, SW; Craig, VSJ; Wanless, EJ; Willott, JD
    Hypersaline environments are ubiquitous in nature and are found in myriad technological processes. Recent empirical studies have revealed a significant discrepancy between predicted and observed screening lengths at high salt concentrations, a phenomenon referred to as underscreening. Herein we investigate underscreening using a cationic polyelectrolyte brush as an exemplar. Poly(2-(methacryloyloxy)ethyl)trimethylammonium (PMETAC) brushes were synthesised and their internal structural changes and swelling response was monitored with neutron reflectometry and spectroscopic ellipsometry. Both techniques revealed a monotonic brush collapse as the concentration of symmetric monovalent electrolyte increased. However, a non-monotonic change in brush thickness was observed in all multivalent electrolytes at higher concentrations, known as re-entrant swelling; indicative of underscreening. For all electrolytes, numerical self-consistent field theory predictions align with experimental studies in the low-to-moderate salt concentration regions. Analysis suggests that the classical theory of electrolytes is insufficient to describe the screening lengths observed at high salt concentrations and that the re-entrant polyelectrolyte brush swelling seen herein is consistent with the so-called regular underscreening phenomenon. © the Owner Societies 2023 This article is Open Access - CC-BY-NC