# Stabilization of Pickering Emulsions by Hairy Nanoparticles Bearing Polyanions
## 4 Conclusions  
Compared to the articles concerning preparation of Pickering emulsions based on nanoparticles bearing hairy chains [42; 43; 44; 45; 46; 47; 48], this work not only focuses on the preparative conditions during the formation of Pickering emulsion, but also monitors the Pickering emulsion stability with time after preparation. It was found that both formation and stability of Pickering emulsion depend on the competition of thermodynamic and kinetic behavior during the preparative and standing process. A hairy nanoparticle bearing polyanions called poly (sodium \(p\)-styrenesulfonate) (PS@PSS) was applied as a solid nanoparticle to stabilize the water/oil interface during the Pickering emulsion formation. The optimized ultrasonic power is 150 W and the ultrasonic time is 3 min. It was found that low ultrasonic power or a short ultrasonic time could not provide enough ultrasonic energy for PS@PSS nanoparticles to migrate from water phase to the water/oil interface, while high ultrasonic power or a long ultrasonic time would damage the nanoparticle surface and lead to aggregation in the oil phase, which has not been reported elsewhere. Ripening of obtained Pickering emulsion occurred in 30 min, and then would be stable for three months, which is similar to what has been reported by other solid particle stabilized Pickering emulsion system [38]. The ripening could also be reduced by introducing more a hydrophobic oil phase, i.e., hexadecane, compared to a short-chain alkane like decane. Relatively homogeneous Pickering emulsion was observed at low ionic strength (0.1 mM),  
Figure 9: (**a**) Optical images of hexadecane/H\({}_{2}\)O Pickering emulsions stabilized by PS@PSS with different concentrations after standing for 10 min; (**b**) Microscope images of hexadecane/H\({}_{2}\)O Pickering emulsion stabilized by PS@PSS with different concentrations. Here the ultrasonic power is 150 W, salt concentration is 0.1 mM, ultrasonic time is 3 min, and water:oil ratio is 1:1. The bar is 10 \(\upmu\)m. (**c**) Droplets size distribution in number corresponding to microscope images. while heterogenous emulsion with a larger size was obtained at high ionic strength up to 10 mM. However, Pickering emulsion was hardly formed at 100 mM due to extreme hydrophobicity of the particle, a phenomenon similar to a system based on clay [38]. The optimized water:oil ratio is 1:1, and no stable emulsion was prepared when water:oil ratio was lower than 1:1 because of the hydrophilic nature of PS@PSS. Once water:oil ratio was over 1:1, lower water:oil ratio resulted in larger emulsion droplets and more emulsion volume fractions, which was also observed in hematite particle stabilized Pickering emulsions [49]. This work paves the way for Pickering emulsion formation and stabilization mechanism that Pickering emulsion equilibrium could be broken as long as the ultrasonic energy or external stimuli is large enough to migrate solid particles from interface to bulk phase. This finding not only provides the basis for preparing Pickering emulsions with superior stability and a long-term guarantee period, but also is extremely pertinent when designing Pickering emulsions for use in controlled stabilization and destabilization applications such as drug delivery and oil harvesting. Further study is needed to investigate the influence of hairy nanoparticles with different structures on the formation, microstructure, and stability of Pickering emulsion to confirm the proposed mechanism and potential application in such as controlled drug release is also under the way. The following are available online at [[http://www.mdpi.com/2073-4360/11/5/816/s1](http://www.mdpi.com/2073-4360/11/5/816/s1)]([http://www.mdpi.com/2073-4360/11/5/816/s1](http://www.mdpi.com/2073-4360/11/5/816/s1)), Figure S1: Schematic diagram (a) and photo (b) of the home-made photoreactor, Figure S2: Schematic diagram (a) and photo (b) of ultrasonic homogenizer, Figure S3: The effect of pH on PS@PSS size, Table S1: The effect of pH on PS@PSS size. Conceptualization, K.C., X.G.