Fig. 3.

SLD profiles corresponding to the NR fits of Fig. 2 for an OTS monolayer in different environments, as indicated. The lines at z = 0 and 26.3 Å represent the average positions of the OTS monolayer. For example, the line at 37.6 Å represents the 50% water density (midpoint of the sigmoidal profile) for untreated (naturally aerated) D₂O. The in-plane average coherent SLD profile, β(z), normal to the quartz surface is directly proportional to the mass density of the medium, ρ(z). Inset shows a snapshot of a different molecular distribution (in comparison with one shown in Fig. 1) that is also consistent with the data for naturally aerated water, where local random diffuse density fluctuations (with a maximum possible lateral spacing, Y, of 10 μm with no minimum limit) are shown based on expectations from computer simulations (25, 39, 40). Other molecular models also can fit the data, such as small fluctuating cavities of about the same size as those shown here but with sharper liquid–vapor interfaces.