# An Oligoimide Particle as a Pickering Emulsion Stabilizer
## 3 Results and Discussion
### Characterization and Dispersion of Oligoinide Particles  
The PMDA-ODA particles were dispersed into water or decalin, and the stabilities of the resulting dispersions were evaluated (Figure 2). For comparison, PMDA-ODA particles prepared in NMP were also tested. After the particles were ground and sieved with a 200 \(\upmu\)m aperture sieve, they were dispersed in distilled water or decalin. Sieving was conducted to remove very large particles in order to rule out the possible effect of them on dispersion. After ultrasonication at a frequency of 30 kHz for 30 min, the dispersions were sieved again with a 25 \(\upmu\)m aperture sieve. The dispersions just after ultrasonication and sieving are shown in Figure 2 (left). The amount of particles that passed through the sieves and that were uniformly dispersed was much greater in the case of the particles synthesized in water. After storing the samples for 48 h, the particles synthesized in water were still stably dispersed, but the particles synthesized in NMP settled at the bottom of the vial (Figure 2, right). This indicates that the oligoinide particles synthesized in water have a good dispersion stability in both water and decalin, but the particles synthesized in NMP do not. Most PMDA-ODA particles prepared in NMP were greater than 30 \(\upmu\)m in size after ultrasonication (Figure S2a). Because it was thought that the poor dispersion of the particles synthesized in NMP might be due to their large size, ball milling was conducted to prepare finer parti \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Yield (\%)**} & \multirow{2}{*}{**Inherent Viscosity 1 **} & \multirow{2}{*}{**DI 2 **} & \multicolumn{2}{c}{**Thermal Properties (\({}^{\mathrm{c}}\)C)**} \\ \cline{3-5}  & & & \(\mathbf{T_{S}}\)3 **} & \multicolumn{2}{c}{**T\({}_{10}\)4 **} & \multicolumn{2}{c}{**T\({}_{\mathrm{g}}\)5 **} \\ \hline
97 & 0.15 & 95 & 476 & 513 & 352 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Yield, viscosity, degree of imidization (DI), and thermal properties of PMDA-ODA synthesized in water. Figure 2: Photographs of dispersions of PMMA-ODA particles in water (**top**) and decalin (**bottom**) synthesized using (**a**) water and (**b**) NMP. The photographs were taken just after ultrasonication/sieving and after storing the samples for 48 h at room temperature. ball mill with a speed of 800 rpm for 22 h. The sizes of resultant particles were greater than 5 \(\upmu\)m, as shown in Figure S2b. The ball-milled particles were dispersed in water or decalin by homogenizing them, but a stable dispersion could not be obtained. The incapability of the particles prepared in NMP to form a stable dispersion may be attributed to their size being bigger than colloidal size. Therefore, the following experiments were conducted using the PMDA-ODA particles synthesized in water. As shown in Figure 3a, the pristine PMDA-ODA particles synthesized in water had a size range of 1-5 \(\upmu\)m. When they were put into water, a homogeneous dispersion could not be obtained. Ultrasonication of the dispersion effectively broke the particles into much smaller 100-300 nm sized particles (Figure 3b), which were stably dispersed in water and decalin as described above. It was confirmed that FT-IR spectra of the oligoimide particles before and after ultrasonication were practically identical, indicating that any chemical change did not occur upon sonication. It was found that the ultrasonicated particles had a plate-like shape (Figure 3b). Among reported Pickering emulsion stabilizers, clay and layered double hydroxide (LDH) particles have a plate-like shape and produce stable emulsions [8; 39; 40; 41; 42]. The size distribution of the PMDA-ODA particles was investigated using dynamic light scattering (DLS) (Figure 4). The mean size of PMDA-ODA particles was 221 nm (polydispersity index (PDI) = 0.226). The DLS result would be a rough measure of the lateral size distribution of the PMDA-ODA particles because DLS analysis assumes spherical shapes [43; 44].