## 3 Results and Discussion
### St-Co-DVB Polymerization in the Presence of Flocculated SNPs  
The polymerizations in emulsions with alkaline pH yielded the formation of St-co-DVB copolymer microspheres partially covered by SNPs. In Figure 1, it can be observed that in all samples, polydisperse submicronic St-co-DVB microspheroidal particles were obtained. It is also clear that the SNPs were highly aggregated at pH = 9. The DVB, due to its difference of reactivity with St, interferes in the nucleation and the polymerization growth process and disturbs the polymerization mechanisms, even at low concentration, inducing the production of irregular-shaped latex particles [41; 42; 44; 53]. DVB is more reactive than St and reacts with VBS, a soluble monomer, in the early stages of the reaction. From DLS measurements and for all runs, as shown in Figure 2, the average polymer particle size fluctuated between 100 and 2000 nm. These results can be attributed to the heterogeneous covering of the polymer particles by the flocculated SNPs during the reaction, along with the formation of irregular-shaped polymer particles, such as spheroidal or ellipsoidal, due to the different reactivities of St and DVB. Moreover, the polydispersity index (PDI) of the DLS measurements were 0.269, 0.308, and 0.558 for 1, 2, and 3%, respectively, which indicated heterogeneity of the microsphere dispersions [54]. Figure 1: TEM images of the St-co-DVB polymer prepared in Pickering emulsion polymerization at pH = 9: (**A**) 1 wt% DVB, (**B**) 2 wt% DVB, and (**C**) 3 wt% DVB. Although St-co-DVB polymerization has been extensively studied in dispersion suspension and emulsion polymerizations, few works have been reported on the preparation of copolymer particles of submicron size in Pickering emulsions. [PERSON] et al. [46] reported the preparation of poly(St-DVB) nanospheres with a uniform average size of 100 nm by photocatalytic Pickering emulsion polymerization using titania hydrosols, modified by the adsorption of surfactants. Nevertheless, the monomer dispersed phase content was poor; only 4 wt% monomers (1.05 g St + 0.15 g DVB) were introduced into a 50 mL glass flask containing a high concentration of titania nanoparticles (i.e., approximately 33 wt%, with respect to monomers). The authors proposed a mechanism based on nucleation that occurred inside the surfactant-titania aggregates, which acted as micelles. The nuclei formed inside the aggregates grew via monomer swelling, giving rise to the formation of nanometric mature copolymer particles. [PERSON] et al. [47] also prepared microspheres of submicrometric sizes, by emulsion polymerization, but their method required large amounts of surfactants. In addition, surfactants are costly and environmentally unfriendly, and they can also affect the properties of the polymeric materials due to their desorption during further polymer handling, so it is preferable to avoid using them. Precipitation polymerization as a surfactant-free method for preparing poly(St-co-DVB) particles represents a good alternative, but this method gives rise to the formation of micron-sized particles [54; 55]. In another study, the St Pickering emulsion polymerization at a relatively high polymer content was proposed using a soluble co-aid at low concentration [56]. In these conditions, as soon as the water-soluble initiator is added to the reactor, radicals are formed due to its homolytic decomposition, which will then react with the vinyl groups of VBS monomers, distributed in the three-dimensional SNPs' network. As VBS is water soluble, it reacts faster than the low-soluble hydrophobic monomers and therefore promotes the nucleation step by the formation of oligomers. These oligomers will then grow and aggregate to reduce their specific charge area to form precursor polymer particles that will then further grow by monomer swelling.