Adhesion of alumina surfaces through confined water layers containing various molecules

When two surfaces confine water layers between them at the nanoscale, the behavior of these confined water molecules can deviate significantly from the behavior of bulk water, and it could reflect on the adhesion of such surfaces. Thus, the aim of this study is to assess the role of confined water layers on the adhesion of hydrophilic surfaces and how sensitive this adhesion is to the presence of contaminants. Our methodology used under water AFM force measurements with an alumina-sputtered sphere-tipped cantilever and a flat alumina single crystal and then added fractions of ethanol, dimethylformamide, formamide, trimethylamine, and trehalose to water as contaminants. Such solutions were designed to illuminate the influences of dielectric constant, molecular size, refractive index, and number of hydrogen bonds from donors and acceptors of solutes to water. Apart from very dilute solutions of dimethylformamide, all solutions decreased the ability of confined water to give adhesion of the alumina surfaces. The predicted theoretical contribution of van der Waals and electrostatic forces was not observed when the contaminants distorted the way water organizes itself in confinement. The conclusion was that adhesion was sensitive mostly to the hydrogen-bonding network within water layers confined by the hydrophilic alumina surfaces.