Slide 9 of 12
Notes:
The first set of experiments shows excellent agreement with the theory. A drop of n-hexadecane and a polystyrene sphere are stable to coalescence.
The inset shows the example curve for 0.1 mM sodium nitrate on a log plot to expand the weak double-layer overlap. Experiments at several electrolyte concentrations show this interaction is monotonically repulsive up to 100 mM. Thus, the hydrophobic interaction is not directly observed.
However, the hydrophobic effect can actually be buried within the film, in a manner of speaking, since the oil drop is too weak to bring the bodies into proximity for the attraction to take over.
Therefore, we can find the largest values of the hydrophobic parameters that still describe the observed behavior. C1 of -2 mN/m and 3 nm for the decay length are typical of the low end for reported measurements with solid-solid interactions.
We might conclude from this that a smaller sphere be used, for example, to create thinner films where the hydrophobic effect is important.
The next experiment we conducted...