Transmission of Visible and Ultraviolet Light through Charge-Stabilized Nanoemulsions

We have studied the transmission of visible and ultraviolet light through uniform silicone oil-in-water nanoemulsions stabilized by an anionic surfactant, sodium dodecyl sulfate (SDS), in the single-scattering limit. As the droplets become significantly smaller than 100 nm, the nanoemulsions still scatter noticeably in the ultraviolet region, yet they become progressively more transparent at visible wavelengths. This transparency can even be enhanced as the droplets are concentrated into a biliquid glass and the nanoemulsion becomes strongly elastic. From the measured transmission intensity as a function of wavelength, droplet radius, and volume fraction, I(λ,a,ϕ), we determine the extinction coefficient. Many qualitative features of the extinction coefficient can be identified using a modified structure factor based on disordered hard spheres and the Mie scattering form factor of isolated spheres. Due to the screened-charge repulsive interactions and the deformability of the droplets, there can be significant quantitative differences between the optical properties of glassy nanoemulsions and hard spheres.