Does zinc oxide lose its UV blocking properties when mixed with oil?

Question

Zinc oxide provides strong protection against UVA and UVB radiation. Does $\ce{ZnO}$ retain this protection when it is dissolved in oil?

When $\ce{NaCl}$ is dissolved in water, the $\ce{Na+}$ and $\ce{Cl-}$ ions are pulled apart by the water molecules. I would assume that a similar thing happens when $\ce{ZnO}$ is dissolved in oil, where the $\ce{Zn^2+}$ is separated from the $\ce{O^2-}$ ions.

Also, according to Wikipedia — Zinc oxide,

ZnO reacts slowly with fatty acids in oils to produce the corresponding carboxylates, such as oleate or stearate.

But that still doesn't tell me whether that would lead to a loss of the UV protective properties.

Answer 1

$\ce{ZnO}$ is not soluble in oils. But it can form dispersion in oils. $\ce{ZnO}$ may react with traces of fatty acids in oils, forming respective zinc salts. But for UV screening context, it is negligible negative effect. $\ce{ZnO}$ does not lose in such a case its properties, there is just little less of it there.

The major factor in UV screening context is difference in refraction indexes of $\ce{ZnO}$ ( or $\ce{TiO2}$ ) particles and the fluid (liquid or gas). The bigger difference means stronger light scattering and longer average UV path through the given layer.

With a longer optical path comes also better UV absorption by the used liquid, more exactly by UV absorption additives.