*3.2. Density Profile*

The alkyl groups in the modified molecules are mixed with the oil phase, and the GO molecules are distributed on the water phase interface because of the polar group -OH. As shown in Figure 6, the oil and water phases are regularly separated by the modified nanoparticle NGOs. To more intuitively observe the self-assembled structure of the NGOs in the oil–water interface layer and the distribution of oil, water, alkyl, and GO molecules at the interface, the density distribution curves of various molecules along the *Z*-axis direction were calculated, as shown in Figure 7. The nanoparticle NGOs formed a more disordered self-assembled interfacial film structure. An analysis of the density profiles showed that a distinct oil–water interface at 35 Å formed after being distributed, and the nanoparticles were mainly found in the interfacial range of 15 Å–45 Å.

**Figure 7.** The density of the components in the oil–water and nanoparticle NGO systems.

As shown in Figure 7, the systems appearing along the *Z*-axis direction are the water phase and NGO–oil phase, with alkyl groups mainly distributed on the oil side. The graphene oxide thin layers are mainly distributed on the water side, forming an interfacial film system at the oil–water interface.
