χ is the attenuation coefficient of hexadecane which was experimentally measured. R1 is determined through supplementary measurements, and the contributions from the substrates-oil interfaces are subsequently subtracted from the total reflectivity (Rtotal). The data is then normalized, and the reflectivity (R2) originating exclusively from the oil-water interface is plotted as a function of the scattering wave vector Q. Q is defined by the beam incident angle θ and the neutron wavelength λ: