## 4 Discussion
### Size of Microspheres Function of NP Type for the Same Monomer  
We have investigated the role of the NPs on the size of microspheres obtained by Pickering emulsion polymerization, by keeping the ultrasonication time constant and utilizing the same monomers. In this case, the only variable that changes is the immersion depth of the NP-Gly, NP-CN, and NP-SH into the polymer. By plotting the size distribution of the polymer microspheres obtained with the NP-Gly, NP-CN, and NP-SH, we find that the average microspheres size increases in the order NP-SH \(<\) NP-CN \(<\) NP-Gly, for the same tBA monomer in the Pickering emulsion generation and polymerization, see Figure 5. The contact angle \(\beta\) of the NP-Gly, NP-CN, and NP-SH with PtBA were also measured from the diameters of the traces left on the microsphere surface and are given in Table 4, and Figures S13 and S14. By analyzing the data in Table 4, a trend emerges, namely the contact angle of the NPs with PtBA increases in the order NP-SH \(<\) NP-CN \(<\) NP-Gly. This indicates that the contact angle or the immersion depth appears to be the main factor \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**NP-SH**} & \multicolumn{2}{c}{**NP-CN**} & \multicolumn{2}{c}{**NP-Gly**} \\ \hline \multirow{3}{*}{**Polymer**} & **Microsphere** & \multicolumn{2}{c}{**Microsphere**} & \multicolumn{2}{c}{**Microsphere**} \\  & **Diameter** & \(\beta^{\circ}\) & **Diameter** & \(\beta^{\circ}\) & **Diameter** & \(\beta^{\circ}\) \\  & **[\(\upmu\)m]** & & **[\(\upmu\)m]** & & **[\(\upmu\)m]** & \\ \hline P(MM) & - & \(106.0\pm 5.2\) & - & \(108.1\pm 2.9\) & 40, 100 & 149.9 \(\pm\) 0.5 \\ P(BM) & 40 & \(118.2\pm 1.9\) & - & \(114.4\pm 2.2\) & 80 & 154.6 \(\pm\) 0.5 \\ P(tBA) & 40 & \(115.7\pm 2.6\) & 80 & \(119.4\pm 1.8\) & 100 & 153.5 \(\pm\) 0.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of microsphere diameter and contact angle \(\beta\) with the polymer; the data for NP-CN and NP-SH were taken from reference [35]. Figure 4: Colloidosome size distribution resulted from Pickering emulsion polymerization obtained from MM, BM, and tBA and stabilized with the NP-Gly. The ultrasonication time for the emulsion was 15 s, for all samples. affecting the curvature of the emulsion droplet and of the resulting polymer microsphere. Based on these experimental findings, we note the critical role played by the NPs contact angle at the three-phase line. In fact, the explanation, we provide next, sheds light into the fundamentals of Pickering emulsion formation, offering direct evidence with respect to one of the main parameters determining the size of the microspheres obtained and above that determinant for the emulsion phase and curvature of the emulsion droplet and consequently of the microspheres' size. In the emulsion theory, such as that of [PERSON] and [PERSON] [37; 54], the emulsion type is thought to be determined by the affinity of the emulsifier surfactant or particle to either the oil or the water phase. In case of surfactants, their affinity to the oil or water phase can be gauged by a post hoc rationalization, thus a semi-quantitative criterion called hydrophilic-lipophilic balance (HLB) emerged. In the case of nanoparticles, however, such a criterion cannot be applied as it is difficult and impossible to measure an HLB value, except for Janus nanoparticles [12; 55]. For homogeneous nanoparticles, we have previously hypothesized [56] that the affinity to either water or oil phases translates into a preferential immersion (or good wettability, low contact angle), of the NPs, into either one phase or the other, which ultimately will determine the curvature of the oil/water interface and the emulsion type, see the discussion in our previous publication and the cartoon in the Figure 6. The NPs' affinity and preferential immersion of the NPs into one phase or the other can be thought of how well the NPs are wetted by one of the phases, and quantitatively by the value of the contact angle.