# An Oligoimide Particle as a Pickering Emulsion Stabilizer
## 3 Results and Discussion
### Oil-in-Water Pickering Emulsions  
Oil-in-water Pickering emulsions were prepared using \(n\)-hexadecane as an oil phase and oligoinide particles as a stabilizer (Table 2, Figures 5 and 6). The emulsions were obtained by adding \(n\)-hexadecane into the aqueous particle dispersions (oil-water volume ratio = 1:6) with different particle wt %. All emulsions obtained were confirmed to be oil-in-water type based on conductivity values higher than 1 \(\upmu\)S cm\({}^{-1}\)[34; 45]. This was also supported by drop tests. The percentage of emulsion remaining for 48 h was calculated based on Equation (2), and we found that almost all emulsion droplets survived because no oil-water separation was observed. This result indicates that the Pickering emulsions were completely stable for 48 h after emulsification in the PMDA-ODA particle concentration range from 1.0 to 0.1 wt %. The oil-in-water Pickering emulsions that were stored for 48 h are shown in Figure 5. Although slow creaming was observed with time, the emulsions returned to their original homogeneously dispersed state by light shaking. With increasing storing time, the emulsion layer heights gradually reduced. For example, in the case of the 1.0 wt % particle concentration emulsion, the emulsion layer height reduced to about a half of the original height three months after preparation. It was later found that the Pickering emulsions were stable for six months without phase separation. The mean oil droplet diameters were measured and ranged from 11 to 118 \(\upmu\)m. There is a clear trend of decreasing oil-in-water emulsion droplet size with increasing particle concentration, which can be observed in Table 2 and Figure 6. This can be explained by the smaller emulsion droplets having a larger surface area that can be stabilized by a larger amount of oligoinide particles. The size distribution of the oil droplets is shown in Figure S3. In addition to the 1:6 oil-water volume ratio, the 1:1 decalin-water volume ratio was also tested and oil-in-water Pickering emulsions were obtained (particle concentration = 1.0 wt %) (data not shown). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Particle** & **pH of** & **Conductivity of** & **Conductivity of** & **Type of** & **Emulsion** & **Mean Droplet** \\
**Concentration** & **Dispersion** & **Dispersion** & **of Emulsion** & **Emulsion** & **Remaining for** & **Diameter**\({}^{\text{c}}\) \\
**(wt \%)** & **Dispersion** & **(\(\upmu\)S cm\({}^{-1}\))** & **(\(\upmu\)S cm\({}^{-1}\))** & **Formed**\({}^{\text{a}}\) & **48 h b (\%)** & **(\(\upmu\)m)** \\ \hline
0.1 & 4.88 & 60 & 44 & Oil-in-water & \(\sim\)100 & \(\sim\)118 \\
0.2 & 4.47 & 111 & 98 & Oil-in-water & \(\sim\)100 & \(\sim\)45 \\
0.5 & 4.10 & 243 & 201 & Oil-in-water & \(\sim\)100 & \(\sim\)19 \\
1.0 & 4.02 & 287 & 239 & Oil-in-water & \(\sim\)100 & \(\sim\)11 \\ \hline \hline \end{tabular}  
* Determined by emulsion conductivity measurements and drop tests. \({}^{\text{b}}\) Calculated using Equation (2). \({}^{\text{c}}\) Measured using an optical microscope from a data set of at least 1000 measurements for each sample.  
\end{table} 
Table 2: Properties of the Pickering emulsions of \(n\)-hexadecane stabilized by PMDA-ODA particles with different concentrations (oil-water volume ratio = 1:6). It has been reported that the stability of Pickering emulsions based on conventional solid particles can often be influenced by pH [46; 47; 48]. In this case, pH adjustment of the dispersion medium is generally required to prepare stable emulsions. In the present study, it should be noted that stable emulsions were prepared using the oligoimide particles without pH adjustment. To investigate the applicability of the oligoimide stabilizer to various oils, \(n\)-hexadecane, linseed oil, olive oil, and phenyl acetate were used as oil phases to prepare Pickering emulsions at a particle concentration of 0.5 wt % (Table 3) The pH and conductivity of the aqueous particle dispersion were 4.10 and 243 \(\mu\)S cm\({}^{-1}\), respectively.