# Stabilization of Pickering Emulsions by Hairy Nanoparticles Bearing Polyanions
## 3 Results and Discussion
### Ultrasonic Power and Time
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Entry** & **Diameter (nm) 1** & **Thickness (nm) 2** & **PDI 1** \\ \hline PS@PSS (untreated) & 252 \(\pm\) 1.2 & 89 \(\pm\) 0.8 & 0.018 \(\pm\) 0.009 \\ PS@PSS (100 W) & 249 \(\pm\) 0.9 & 88 \(\pm\) 0.6 & 0.027 \(\pm\) 0.013 \\ PS@PSS (150 W) & 247 \(\pm\) 1.4 & 86 \(\pm\) 0.9 & 0.022 \(\pm\) 0.008 \\ PS@PSS (200 W) & 239 \(\pm\) 2.7 & 82 \(\pm\) 1.5 & 0.056 \(\pm\) 0.021 \\ PS@PSS (300 W) & 236 \(\pm\) 1.8 & 81 \(\pm\) 1.1 & 0.037 \(\pm\) 0.015 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Size of PS@PSS after homogenizer treatment under different powers. Figure 3: (**a**) Optical images of hexadecane/H\({}_{2}\)O Pickering emulsion stabilized by PS@PSS under different ultrasonic powers. Here the water:oil ratio is 1:1, salt concentration is 0.1 mM, and ultrasonic time is 3 min. The bar is 10 μm. (**b**) Pickering emulsion droplet size distribution in number corresponding to microscope images. (**c**) Contact angle images of a water droplet on the glass plate coating with PS@PSS nanoparticles and contact angle data of PS@PSS after homogenizer treatment under different powers. The particle migration may cause the decrease in Pickering emulsion droplets when the ultrasonic power rose from 150 W to 200 W. Low power could not provide sufficient energy to \"transport\" the PS@PSS nanoparticles to the interface of hexadecane and water phase; thus, ultrasonic power (100 W) was too low to form complete Pickering emulsion, and the well-dispersed situation could not reached. High power could affect the droplet size and the stability of Pickering emulsion. When the ultrasonic power increased from 100 W to 150 W, the ultrasonic energy strongly pushed PS@PSS that existed in water phase previously to the interface of water and hexadecane. After withdrawal of the homogenizer, the PS@PSS anchored at the interface was thermodynamically stable. When the ultrasonic power continued to increase up to 200 W, Pickering emulsion droplet size became larger and inhomogeneous. This effect likely occurred because the greater ultrasonic energy created partial PS@PSS that had anchored at the water/hexadecane interface migrated back into the water phase. This is similar to the breaking of a conventional emulsion by mechanical stirring. A special emulsion was formed when the ultrasonic power increased up to 300 W. The image shows some inhomogeneous clustering in the oil phase of the Pickering emulsion droplets. There were two reasons that could explain this phenomenon. First, higher ultrasonic power further broke the polymer chains of partial PS@PSS, and the particle size became smaller. This made some emulsion droplets become larger. Second, the ultrasonic power (300 W) was so strong that the hairy polyelectrolytes in some PS@PSS decreased dramatically from 252 nm to 236 nm as shown in Table 2. This increased the hydrophobicity and made them aggregate and migrate into the inner oil phase. Sonication time was another vital factor of Pickering emulsion preparation. As shown in Figure 4, the system consisting of oil phase, water phase, and PS@PSS varies with ultrasonic time. When the sample was homogenized for only one minute, there was a layer of oil phase floating on the Pickering emulsion (inset in Figure 4a). The images also illustrate that droplets of one minute-made emulsion were fairly rare, and the PS@PSS were not dispersed uniformly in the system (Figure 4b). Thus, both the macroscopic phenomenon and microscopic images illustrated that the ultrasonic time was too short to form Pickering emulsion completely. The Pickering emulsion droplets were uniform and homogenous when the ultrasonic time extended to 2-3 min. At longer time periods, we found that the average droplets size of emulsions shown in Figure 4c were 5.8 and 5.0 \(\upmu\)m, respectively. This led to a slight decreasing trend. Furthermore, the quantity of emulsion droplets also decreased obviously when the ultrasonic time increased to 4 min. Even at 5 min, the PS@PSS aggregated inside the oil phase (Figure 4b).