The search for Nanobubbles by using specular and off-specular Neutron Reflectivity

In this work we show an example where specular and off-specular neutron reflectivity can give insight into the structure of solid/liquid interfaces. The presence of nanobubbles and/or a depletion layer at the interface has been long discussed and generated a plethora of controversial scientific results. By means of time of flight neutron reflectometry (NR) and grazing incidence small angle scattering (GISANS), we studied the interface between hydrophobized silicon and heavy water in normal and nigrogen gas enriched state. Our results from the specular reflectivities can be explained without an assumption of a depletion layer and the off-specular measurements show no change with nitrogen super saturated water, which is consistent with the assumption that no nanobubbles are present. We discuss the experiments, in terms of the maximum surface coverage of nanobubbles that could be present on the hydrophobic surface compatible with the limit of sensitivity of NR and GISANS.