, where Φ 6 and Nbi are the volume fraction and scattering length density of component i, respectively. The use of hydrogen-deuterium substitution (H/D) in water has been prevalent in neutron experiments due to the contrasting scattering lengths of hydrogen ( 1 H, -3.74 × 10 -5 Å) and deuterium ( 2 H, 6.67 × 10 -5 Å). Consequently, the Nb values for H2O and D2O exhibit a notable disparity: -0.56 × 10 -6 Å -2 and 6.35 × 10 -6 Å -2 , respectively. A desired contrast for the aqueous phase can be achieved by varying the mixing ratio between H2O and D2O to highlight the scattering of different aspects of the sample under study. NR profiles from aqueous phases with distinct contrasts were concurrently fitted to a single model. This constraint of a unified model for all contrasts facilitates the deduction of a unique and well-defined structural model. The NR data were analysed employing the exact optical matrix method as previously reported . The analysis involved fitting the NR data to predefined models incorporating parameters such as SLD, thickness, solvent content, roughness, and the number of layers, thereby calculating corresponding reflectivity profiles. These profiles were then compared with experimental data, and the fitting process was iterated until minimizing differences between the global fit and experimental data across various isotopic contrasts. The optimized fitted parameters were amalgamated to generate the scattering length density profile of the sample, reflecting the variation in composition perpendicular to the interface.