# Stabilization of Pickering Emulsions by Hairy Nanoparticles Bearing Polyanions
## 3 Results and Discussion
### Ultrasonic Power and Time
The particle size distribution shown in Figure 4c was similar with that when ultrasonic power was 300 W. One explanation for these changes in Figure 4a (1 min) was the migration of PS@PSS nanoparticles. It took some time for ultrasonic energy to migrate PS@PSS from water phase to the interface of hexadecane and water. Thus, when the ultrasonication time was 1 min, a floating oil layer existed with unstable emulsion. The ultrasonication energy from the extra 2 min was convenient and facilitated the formation of Pickering emulsions, at the same time droplets size was getting smaller, which was also observed in the previous report [35]. It was concluded that in order to stabilize the droplets, more particles were absorbed to the W/O interface with shear time. Despite the accumulation effect of ultrasonic energy on particle migration, the PS@PSS size after ultrasonic treatment under different times was analyzed by DLS (Table 3). In general, with increasing ultrasonication time, the PS@PSS size decreased somewhat even though the change was relatively small. This strengthens the PS@PSS hydrophobicity and decreases emulsion droplet size. Figure 4b (5 min) shows that a long time also led to PS@PSS aggregation and migration to the inner oil phase. It was found that PDI of PS@PSS treated for 5 min increased a lot (0.068) compared to its original PDI (0.011), which may result in part PS@PSS with a short hairy layer and loss of its hydrophilicity and finally shifted to the oil phase with a long ultrasonic treatment time. Changes in polymer structure can be created during ultrasonic treatment as a result of cavitation and research has suggested that chain cleavage could occur preferentially at weak spots in the chain [36]. PS@PSS hairy nanoparticles used in this paper is a special fuzzy structure of dense core and loosened shell, so the thickness decrease in PS@PSS shown in Table 2 happened gradually from the chains outside to the inner side [37]. Both ultrasonic power and ultrasonic time were significant factors for the formation of Pickering emulsions. Low power and short time could not provide enough ultrasonic energy for PS@PSSnanoparticles to migrate from the water phase to the water/oil interface; excessive power and long-term formation of PS@PSS aggregation broke the balance that had been formed previously. Therefore, when the ultrasonic power was 150 W and ultrasonic time was 3 min, high-quality hexadecane/H\({}_{2}\)O Pickering emulsions stabilized by PS@PSS were prepared and well-dispersed droplets were achieved. Here, the water:oil ratio was 1:1 and the salt concentration was 0.1 mM, which was investigated later in this study. Figure 4: (**a**) Optical images of hexadecane/H\({}_{2}\)O Pickering emulsion stabilized by PS@PSS under different ultrasonic time. (**b**) Microscope images of hexadecane/H\({}_{2}\)O Pickering emulsion stabilized by PS@PSS under different ultrasonic time. Here the water:oil ratio is 1:1, salt concentration is 0.1 mM, and ultrasonic power is 150 W. The bar is 10 \(\upmu\)m. (**c**) Droplets size distribution in number corresponding to microscope images. \begin{table}
\begin{tabular}{c c c c} \hline
**Entry** & **Diameter (nm) 1** & **Thickness (nm) 2** & **PDI 1** \\ \hline PS@PSS (1 min) & 248 \(\pm\) 0.9 & 87 \(\pm\) 0.6 & 0.011 \(\pm\) 0.002 \\ PS@PSS (2 min) & 246 \(\pm\) 0.4 & 86 \(\pm\) 0.4 & 0.032 \(\pm\) 0.013 \\ PS@PSS (3 min) & 243 \(\pm\) 0.4 & 85 \(\pm\) 0.4 & 0.027 \(\pm\) 0.010 \\ PS@PSS (4 min) & 242 \(\pm\) 0.3 & 84 \(\pm\) 0.3 & 0.047 \(\pm\) 0.018 \\ PS@PSS (5 min) & 241 \(\pm\) 0.2 & 83 \(\pm\) 0.3 & 0.068 \(\pm\) 0.024 \\ \hline \end{tabular}  
* Measured by DLS and took the average as the result. 2 Calculated using PS@PSS diameter minus PS core diameter and then divided by two.  
\end{table} 
Table 3: Size of PS@PSS after homogenizer treatment under different time.