# Synthesis of Covalently Cross-Linked Colloidosomes from Peroxidized Pickering Emulsions
## 3 Results and Discussion
### Colloidosome Preparation  
In this study, the \"soft template\" approach [10] was used in which liquid droplets of Pickering emulsion serve as templates for cross-linked colloidosomes synthesis (Figure 1). To synthesize colloidosomes, a combined initiation mechanism was applied, i.e., initiation in a bulk template (with AIBN) and initiation from the surface of the peroxididized latex particles (with the  
Figure 4: (**A**) Diamenter and (**B**) \(\zeta\)-potential variations of peroxididized latex particles synthesized at 85 \({}^{\circ}\)C at different pH levels and PM-2-MAc concentrations. Figure 5: Amount of: (**A**) carboxyl groups; and (**B**) PM-2-MAc copolymers on peroxididized latex particles synthesized at different pH levels. inisurf). Depending on the composition of a monomer mixture, polystyrene, poly(butyl acrylate), or poly(styrene-_co_-butyl acrylate) (all polymers cross-linked with divinylbenzene) were formed in the bulk template during polymerization. The formed polymers are insoluble in hexadecane. As a result, their macromolecules were localized at the interface and were involved in the formation of the colloidosomes' polymer walls (Figure 1C). The peroxide groups localized at the interface (on the surface of peroxid oxidized latex particles) in turn generate free radicals, which participate in radical reactions of initiation, chain transfer, and combination. Due to the above-mentioned radical processes, polymer chains from the monomers and the divinylbenzene cross-linker grew both in the bulk template and from the interface. This resulted in the formation of intermolecular cross-links and the covalent immobilization of the latex particle, which acted as a Pickering stabilizer, within the colloidosome walls. The formation and stability of a Pickering emulsion depend on the latex particles' surface activity (surface HLB). Therefore, the ability to control the HLB of the particle surface is crucial. To confirm that peroxididized latex particles can be used in Pickering emulsion formation for covalently cross-linked colloidosome synthesis, a series of Pickering emulsions was prepared. First, the formation and stability of a series of formulated Pickering emulsions were studied as a function of pH (Figure 6). It was found that there is an optimum pH range in which superior Pickering emulsion stability can be achieved. Notably, at pH < 3 and pH > 9, no emulsion formation was observed, which can be explained by either an absence (pH < 3) or an excessive amount (pH > 9) of ionized carboxyl groups on the latex particles' surfaces, causing the particles to coagulate due to a detrimental HLB change of inisurf macromolecules that act as particle stabilizers. Immediately after formation, a Pickering emulsion \"creams\" by floating an emulsified oil phase on top of an excessive aqueous phase. This effect can be explained by the different densities of the aqueous and oil phases (a large size prevents droplet suspension). At this point, the formulation quality can be assessed by inspecting the aqueous phase for the presence of excessive latex particles. Opalescence and turbidity would signify an inefficient use of latex particles. By adjusting the pH, shear rate, and concentration of latex particles, it is possible to form a clear (particle-free) aqueous phase, indicating that all particles are involved in droplet stabilization. For the synthesis of colloidosomes, latexes developed at pH 7.5 at 85 \({}^{\circ}\)C in the presence of 1 wt.% (based on monomer weight) inisurf PM-2-MAc were chosen. It was the assumption that while having a smaller amount of carboxyl groups, these latexes exhibit sufficient surface activity to stabilize a Pickering emulsion. After formulating a Pickering emulsion, polymerization was conducted at 80 \({}^{\circ}\)C to yield hollow colloidosomes decorated with peroxididized latex particles. Table 3 presents data on the properties of the synthesized colloidosomes.