PEG 6000, ethanol and acetone were purchased from Sigma-Aldrich. Poly(ethyl acrylate-co-methyl Methacrylate-co-trimethylammoniethyl methacrylate chloride) (Eudragit RS100) were sourced from Evonik Roehm, Darmstadt, Germany. Ultrapure water was generated using the Milli-Q filtration system (Millipore, Saint-Quentin-en Yvelines, France). We used ORO^® palm oil as the oil phase. This oil is extracted from the seeds of the fruit of the oil palm (Elaeis guineensis). All the chemicals were analytical grade and used as received.

According to the axisymmetric drop shape analysis, the dynamic interfacial tension γ was measured with a drop tracker tensiometer (Teclis, Longessaigne, France). A rising drop of oil is formed and maintained in a thermostatically controlled cell filled with an aqueous phase containing the suspension of Eudragit^® RS100 nanoparticles. The shape of the drop was recorded in real time with a video camera. Thus, its Laplacian form gave the values of the interfacial area and the surface tension. All experiments were carried out at 25˚C in triplicate.

The formulation method used is the spontaneous nanoemulsification method. First, a homogeneous organic solution is prepared, which may contain an oil phase, water-miscible organic solvents and polymers. This solution is then injected into an aqueous phase with stirring to form the emulsion. Finally, the various solvents are evaporated under reduced pressure to recover the emulsion/nanoemulsions [21] .

1) Composition of formulations

The ternary diagram presented in Figure 1 shows the different proportions used for the formulations.

Thus, we varied the proportions of oil (from 0.23% to 11.62%) and water (from 81.39% to 92.79%); the quantity of Eudragit RS100 was fixed (6.97%). This diagram will allow us to define 12 different proportions called tubes (T1 to T12) ( Table S1 ). Furthermore, to get an idea of the coverage of the newly created interfaces, we calculated the volume fraction of the dispersed phase.

2) Emulsification

The organic solution was obtained by mixing Elaeis guineensis oil, organic solvents (acetone, ethanol) that are miscible with water and the Eudragit RS100 polymer. This solution was then injected into the aqueous phase, into which we had previously added Polyethylene glycol 6000. The abrupt transition of solvents such as ethanol and acetone to the aqueous phase leads to the formation of droplets or nanodroplets. The acetone and ethanol are then removed by evaporation using a rotary evaporator with a water bath.

Physico-chemical characterization lasted 30 days.

1) Bottle test

The bottle test is a technique that allows you to check over the long term whether there are any instability phenomena such as creaming or sedimentation. Observations were carried out for 30 days. We used 50 mL conical bottles containing the emulsion.

2) Conductivity measurements

The conductivity measurement allowed us to verify the direction of the preparations. It was carried out using an electrode which measures the electrical resistance of the emulsions and for the nanoemulsions the electrophoretic mobility was measured.

3) Droplet size measurements

The technique used is based on the estimation of the mean diameter of the droplets by individual counting for emulsions. The optical microscope Axio Zeiss imager A1 coupled to a computer containing the Axio Vision release software Version 4.5 (Zeiss optical microscope) was used for measurements.

4) pH of the emulsions

The measuring cell is introduced into a 50 mL conical bottle containing the emulsion. Be sure to place the electrode at the emulsified phase for the sediment tubes. The reading time is set to three minutes after insertion of the electrode.

5) Viscosity of the emulsions

It is based on measuring the velocity limit reached by a ball falling into a container containing the liquid whose viscosity is to be determined. Based on Stockes-Einstein’s law, this velocity can be used to determine the viscosity of the liquid.

In this part, we evaluated the impact of Eudragit^® RS100 nanoparticles on the Water/cyclohexane interfacial tension using the axisymmetric drop shape analysis method. First, we measured the surface tension of the interface without nanoparticles to confirm the absence of impurities. The interfacial tension values are between 48 and 50 mN·m⁻¹ ( Figure 2 ).

Analyzing Figure 1 , a strong decrease in interfacial tension was observed for Eudragit^® NPs. Thus, in the first phases of adsorption (t → 0), the interfacial tension decreases rapidly. Subsequently, the decrease in interfacial tension slows down and finally reaches a dynamic equilibrium where the maximum coverage of the interface by the nanoparticles is achieved (t → ∞). These results are identical to those obtained in our previous work with Eudragit^® L100 nanoparticles [21] . Which in our opinion allows us to confirm a good stabilization of the interfacial tension and allows us to affirm that the Eudragit^® RS100 is capable of stabilizing an interface between two immiscible liquids such as oil and water [22] - [26] .

During the visual inspection of the dispersions, the main results showed macroscopically stable and homogeneous dispersions for the majority of the tubes with the appearance over time of an oily supernatant in tubes T8, T9, T10, T11 and T12. This oily supernatant was negligible in tubes T8 and T9 and more significant in tubes T10, T11 and T12. The appearance of this oily supernatant is due to the phenomenon of coalescence and increases in these tubes as a result of the gradual increase in the quantity of oil passing through these tubes. We also noted that tubes T1, T2, T3, T4, T5, T6 and T7 remained intact until the end of the 30-day storage period. However, it should be borne in mind that macroscopic observation alone does not prejudge the stability of the dispersion, as macroscopic observation does not allow us to see oily droplets in the micrometer range.

The direction of dispersions was established using conductivity measurements ( Figure 3 ).

Since the conductivity of a dispersion depends on the nature of its external phase [5] [18] [24] - [27] , the presence of electrolytes in the dispersion results in a non-zero conductivity (from 0.5 to 0.7 mS/cm), further justifying the aqueous nature of the external phase. The results obtained throughout the characterization period show that the dispersions did not undergo any phase inversion. Also, the conductivity values obtained are higher than that of the water used (0.05 μS/cm) for all the formulations. To this end, a series of conductivity measurements were made in parallel with the water-PEG mixture only. We found that by varying the quantities of water for the same quantity of PEG, the conductivity of this mixture also varied. As the amount of water decreased, the solution became increasingly concentrated in PEG and the conductivity increased. We can therefore deduce from this that PEG is one of the factors that favours the increase in conductivity in our dispersions. It should also be added that our results show that the conductivity value for all the tubes varies within the same range over time. This could highlight the stability of the dispersions over time [28] - [31] .

Figure 4 shows the image of the droplets from tubes T4 and T10 obtained with an optical microscope on the first day of characterization. We can see a big difference in size between the droplets from tube 4 and the droplets from tube 10.

Figure 5 shows the evolution of the droplet size of tubes 4 to 12 as a function of the volume fraction of dispersed phase. The horizontal line in red indicates the resolution threshhold (approximately) of the microscope. This means that the droplets from Tubes 1, 2 and 3 could not be observed because of their nanometric size.

We notice that the size of the droplets increases with the evolution of the volume fraction of dispersed phase. The size of the droplets constitutes a very important criterion of stability. It is one of the variables that most influences the sedimentation rate described by Stokes’ law [27] [28] [31] - [33] . Thus, we studied the evolution of the droplet size as a function of the volume fraction of dispersed phase. This volume fraction was obtained by making the ratio of the volume of the dispersed phase to the volume of the dispersing phase. We found that the droplet size increased as the volume fraction of the dispersed phase increased. Indeed, when the volume fraction of dispersed phase increases, new interfaces are created while the quantity of polymers in our dispersions does not vary. Thus, the droplets formed are not entirely covered with polymer. This causes limited coalescence of the droplets leading to an increase in their diameter [29] [30] . Furthermore, the size of the droplets could not be determined for tubes T1, T2, T3 and was difficult to determine for tube T4. Indeed, the optical microscope used for our study did not allow us to observe droplets smaller than around 500 nanometers. Thus, we obtained with the spontaneous nanoemulsification method, depending on the quantity of oil, two types of dispersions. On the one hand Pickering nanoemulsions for an oil volume less than 1 mL and on the other hand Pickering emulsions for an oil volume greater than or equal to 1 mL. All this confirms the principle of spontaneous nanoemulsification which allows nano-droplets to be produced only in the presence of a high solvent/oil ratio [28] [34] - [38] .

Figure 6 shows the evolution of the pH of the formulations as a function of the volume fraction of dispersed phase.

We observe that the pH of the formulations decreases when we increase the volume fraction of dispersed phase. This for the entire storage period. We were able to observe through the results that the Pickering emulsions and nanoemulsions obtained all have an acidic character and that this acidity increases when the volume fraction of dispersed phase becomes greater. This decrease in pH is due to a progressive release of protons in the aqueous phase. These protons can be released from the polymer or oil used in the internal phase [28] .

The viscosity values of the formulations as a function of the volume fraction of dispersed phase are represented in Figure 7 .

Finally, one of our work objectives was to study the viscosity of the formulations. We note that the viscosity is conditioned by the concentration of the formulation. It increases when the volume fraction of dispersed phase becomes increasingly important. Indeed, the viscosity value evolves as the volume fraction of dispersed phase increases. This is explained by the fact that as the volume fraction of dispersed phase increases, emulsions/nanoemulsions become more and more concentrated and more resistant to flow. In addition, it should be noted that from tube 1 to tube 4 the viscosity changes rapidly and goes from 4.1198 × 10⁻³ to 6.6818 × 10⁻³ mPa·s while from tube 5 to tube 12, it increases slowly and passes from 6.3275 × 10⁻³ to 7.5755 × 10⁻³ mPa·s. This difference in the increase in viscosity of nanoemulsions compared to emulsions is due to the stability of the NEs (limited absence of coalescence) and of the hydrodynamic layer surrounding the nanodroplets. These phenomena disappear when the volume fraction of dispersed phase is increased [39] [40] .