# Stabilization of Pickering Emulsions by Hairy Nanoparticles Bearing Polyanions
## 3 Results and Discussion
### Ultrasonic Power and Time  
Ultrasonication is the most frequently used method to apply mechanical forces to synthesize Pickering emulsions. Sonication is also effective in Pickering emulsion preparation because it can simultaneously emulsify and force particle adsorption onto droplet interfaces [33]. Thus, ultrasonic conditions determined whether Pickering emulsion was well prepared or not. We chose ultrasonic power and time as the first two factors because they were key parameters of ultrasonic conditions. Figure 3a shows microscope images of hexadecane/H\({}_{2}\)O Pickering emulsion stabilized by PS@PSS nanoparticles under different ultrasonic powers (100 W, 150 W, 200 W, and 300 W). The droplet size and number distribution were measured and analyzed via Nano Measurer Software (Figure 3b). In this study, all the Pickering emulsions were O/W emulsions due to the hydrophilicity of the hairy nanoparticles. Microscopic observations (Figure 3a) revealed that the droplets size of hexadecane/H\({}_{2}\)O Pickering emulsions stabilized by PS@PSS were the most uniform at 150 W. If the ultrasonic power decreased to 100 W, then the emulsion droplets became inhomogeneous and the droplet amount was relatively small (Figure 3b). If the ultrasonic power increased to 200 W, then the emulsion droplet uniformity was also worse than that under 150 W and the average size decreased to 6.2 \(\upmu\)m. The size analysis in Figure 3b indicated that some droplets became obviously larger and small size droplets came out. Once the ultrasonic power increased to 300 W, Pickering emulsion droplets were much more inhomogeneous and the polarization of the droplet size could not be ignored. Clusters with relatively small particles were observed in the oil phase of a single Pickering emulsion droplet. Thus, the results showed that the distribution of emulsion droplet size was ideally normal around 7.5 \(\upmu\)m when the ultrasonic power was 150 W; this concurred with the microscope images. This demonstrated that the Pickering emulsion was the most stable. Lower ultrasonic power could not form complete emulsions while higher ultrasonic power disturbed the preparation of Pickering emulsions. [PERSON] et al. [34] found that zeta potential of chitosan nanoparticles gradually decreased and Pickering emulsion droplets became more homogeneous when ultrasonic power was tuned from 100 W to 450 W, but more drastic treatments (600 W) were accompanied by an increase in zeta potential. Figure 2: Transmission Electron Microscopy (TEM) images of (a) crosslinked polystyrene (PS) core; (b) PS@PSS hairy nanoparticles. The bar is 200 nm. Ultrasonic power can impact the diameter of PS@PSS nanoparticles. [PERSON] et al. [34] explored particle size distribution of chitosan particles untreated or treated with different ultrasonication power. They found that higher ultrasonication power reduced the particle size. We then investigated the effects of ultrasonic power on PS@PSS nanoparticle size. Table 2 shows the size of PS@PSS by DLS after treatment with an ultrasonic homogenizer under different powers for 3 min. The thickness of PS@PSS decreased markedly at 200 W. The PSS chains of PS@PSS could cleave, and the hydrophilicity of PS@PSS weakened. Thus, larger Pickering emulsion droplets were produced at 200 W. In general, the PS@PSS size decreased with increasing ultrasonic power. Figure 3c shows that the contact angle of PS@PSS increased with ultrasonic power. It was demonstrated that ultrasonic power gave rise to wettability of PS@PSS nanoparticles, resulting in weaker hydrophilicity. This led to an increase in the Pickering emulsion droplet size.