## 4 Results and Discussion  
### Interfacial Activity and Aggregation Behavior of Emulsifiers  
Understanding how emulsifiers behave at the oil-water interface is fundamental to predicting and controlling emulsion stability. This section explores the IFT of various oil systems in the absence of emulsifiers, followed by a detailed analysis of how molecular structure influences emulsifier dispersion, aggregation, and interfacial coverage. The findings are supported by visualizations of concentration profiles and RDFs derived from simulation data, as illustrated in Figure 3.  
The IFT of the oil-water system in the absence of any emulsifier is presented in Figure 3a. The values range from approximately 41.2 mN/m for Oil 5 to 66.4 mN/m for Oil 14. The presence of emulsifiers was excluded in these measurements because emulsifier migration into the water phase deformed the planar interface, making Equation (7) invalid for precise IFT evaluation. This behavior is typically associated with the Marangoni effect,  
Figure 3: Interfacial activity and aggregation behavior of emulsifiers at oil–water interfaces: (**a**) Interfacial tension (IFT) of the oil–water system without emulsifier. (**b–d**) Aggregation behavior of emulsifiers AS1, AS2, and AS3 at the toluene (Oil 11)–water interface. (**e**,**f**) Aggregation behavior of AS2 and AS3 at the ether (Oil 10)–water interface. The black profile indicates the relative concentration of the emulsifier (ordinate) across the interface, with the abscissa representing the distance normal to the interface in units of \(Rc\) (3.23 Å). (**g**,**h**) Radial distribution functions (RDF) of emulsifier molecules in the above-mentioned models. in which surface tension gradients drive interfacial flow and destabilize planar configurations [48]. Among the oil types, amide-based oils (Oil 5-7) displayed the lowest IFT values, averaging around 42-45 mN/m, reflecting strong interfacial activity. This was attributed to their polar functional groups, which enhanced interactions with the aqueous phase. In particular, Oil 5 exhibited the lowest IFT at 41.2 mN/m, while Oils 6 and 7 followed with values of 43.6 mN/m and 44.9 mN/m, respectively. Furthermore, an increasing trend in IFT was observed with longer aliphatic chains within these oils--indicating that extended chains dilute the polar influence of the headgroup, thereby weakening oil-water interfacial interactions. Conversely, ether-based oils (Oil 8-10) exhibited moderate IFT values ranging from 50.3 mN/m (Oil 8) to 52.8 mN/m (Oil 10), due to their lower amphiphilicity. Alkanes (Oil 1-4) and aromatics (Oil 11-14), lacking significant polar functionality, showed higher IFT values: 55.1-62.7 mN/m for alkanes and 64.2-66.4 mN/m for aromatic oils. These results underscore the crucial influence of oil molecular structure--particularly the presence and arrangement of polar groups--on interfacial behavior. A higher balance between hydrophilic and hydrophobic components in oil molecules improves their alignment at the interface, promoting interfacial tension reduction. The aggregation and dispersion behaviors of various emulsifiers at the interface were also examined and are depicted in Figure 3b-f. AS1, which lacks side chains, formed compact nanomicelles composed of 3 to 5 PAC sheets via \(\pi\)-\(\pi\) stacking. Despite this aggregation, the interfacial coverage remained below a monolayer, as reflected in the broad concentration profile in Figure 3b, indicating weak confinement and lower surface activity. In contrast, emulsifiers with side chains--AS2 and AS3--showed enhanced interfacial spreading. For the interfacially inactive Oil 11 (toluene), both emulsifiers formed stable monolayers (Figure 3c,d). However, with interfacially active Oil 10 (ether), AS2 exhibited displacement from the interface due to competition with the oil molecules, resulting in cluster formation (Figure 3e). AS3, due to its side chains oriented perpendicular to the PAC plane, successfully resisted stacking and remained monodispersed at the interface (Figure 3f).