## 3 Results and Discussion  
### SNPs Aggregates and Surface-Modified SNPs  
The bare Ludox CL SNPs are characterized by the presence of aluminol groups on their surface, conferring them a positive charge of about +44 mV and 47.8 mV at pH = 4.5 and 3.5, respectively [48; 50]. Thus, as soon as VBS was added to the water phase at pH = 5, it adsorbed onto the nanoparticles' surface via its anionic sulfonate group through electrostatic interactions, also inducing a variation in the SNPs' hydrophilicity. Therefore, to enhance the affinity of the SNPs with growing oligomers during polymerizations, the VBS monomer with a dual functionality was used. On the one hand, it can react with the other monomers, due to its vinyl group, and on the other hand, it adsorbs onto the cationic silica nanoparticles.  
However, the aluminol groups of the Ludox CL SNPs are amphoteric; therefore, a pH modification alters their charge. Consequently, the polymerization reaction must be performed at a constant pH to avoid any change in the functionality of SNPs during the reaction, considering that the initiator thermal decomposition produces hydronium ions. Indeed, as reported in the literature [48; 49], the zeta potential value of bare Ludox CL SNPs is affected by the pH of the aqueous phase, exhibiting an isoelectric point at pH = 8.6. Therefore, it is concluded that the SNPs in the emulsions at pH = 9 are highly flocculated, forming a three-dimensional network [29; 51]. Additionally, at this pH, VBS does not interact with the SNPs, because both are negatively charged [48; 49]. As a result, VBS should be considered as a co-aid or nucleating agent in the polymerizations performed in the emulsions at pH = 9. That being so, the addition of buffers allows keeping the pH almost constant and thus guaranteeing the SNPs' aggregated state during the reaction. In such a case, the formation of St-co-DVB microspheres will be promoted through a limited homogeneous coagulative nucleation process, which will be discussed in the next section. The reactions performed at pH values far away from the ones corresponding to the SNPs' isoelectric point favor the dispersion of the SNPs. Thus, the homogeneous coagulative nucleation would be promoted, leading to the formation of larger microspheres. Similarly, pH = 5 must also be kept constant, on the one hand, to favor a rapid adsorption of VBS onto the SNPs' surface and, on the other hand, to avoid the SNPs' decomposition and destabilization that could occur if the pH reaches values lower than 3.5 [52].  
In our previous work [37], the zeta potential of the VBS surface-modified SNPs was measured, and it was observed that the VBS-SNPs were weakly flocculated between pH 3.5 and 5. In this pH range, the inorganic particles exhibited a relatively high zeta potential value at almost +30 mV, which was characteristic of a stable colloidal suspension. Consequently, VBS concentration and pH are predominant variables in the polymerization mechanisms that control the morphology, size, and structure of the final copolymer hybrid materials. In the polymerization runs at pH = 5, the SNPs are slightly flocculated and are surface-functionalized by the presence of vinyl groups oriented toward the aqueous phase. It is worth noting that the VBS concentration has been optimized to perform polymerization in acid emulsions. The density of the adsorbed VBS anions is 0.132 nm\({}^{-2}\), which is equal to 60 VBS molecules surrounding one silica nanoparticle.