Abstract
A novel neutron and X-ray reflectometry sample environment is presented for the study of surface-active molecules at solid–liquid interfaces under shear. Neutron reflectometry was successfully used to characterise the iron oxide–dodecane interface at a shear rate of 7.0times {}10^{2}hbox {s}^{-1} using a combination of conventional reflectometry theory coupled with the summation of reflected intensities to describe reflectivity from thicker films. Additionally, the structure adopted by glycerol monooleate (GMO), an Organic Friction Modifier, when adsorbed at the iron oxide–dodecane interface at a shear rate of 7.0times {}10^{2}hbox {s}^{-1} was studied. It was found that GMO forms a surface layer that appears unaltered by the effect of shear, where the thickness of the GMO layer was found to be 24.3^{+9.9}_{-10.2} Å under direct shear at 7.0times {}10^{2}hbox {s}^{-1} and 25.8^{+4.4}_{-5.2} Å when not directly under shear. Finally, a model to analyse X-ray reflectometry data collected with the sample environment is also described and applied to data collected at 3.0times {}10^{3}hbox {s}^{-1}.
Highlights
A novel neutron and X-ray reflectometry sample environment is presented for the study of surfaceactive molecules at solid–liquid interfaces under shear
The structure adopted by glycerol monooleate (GMO), an Organic Friction Modifier, when adsorbed at the iron oxide–dodecane interface at a shear rate of
The greater meniscus width at the higher shear rate can be considered a result of increasing the angular velocity of the roller, since increasing the roller horizontal velocity had a negligible effect on the meniscus width
Summary
A novel neutron and X-ray reflectometry sample environment is presented for the study of surfaceactive molecules at solid–liquid interfaces under shear. The structure adopted by glycerol monooleate (GMO), an Organic Friction Modifier, when adsorbed at the iron oxide–dodecane interface at a shear rate of was studied. The behaviour of surface-active molecules (surfactants) at solid–liquid interfaces is of key importance to applications such as detergency, froth flotation and lubrication. In such processes adsorbed additives are subject to shear from the surrounding fluid, where the shear rate dictates the extent to which adsorbate molecules are perturbed from their adsorbed structure under static conditions. Shear rates across these example applications are estimated to vary between 102–108 s−11,2
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