## 3 Results and Discussion
### Influence of the Surfmer Concentration on NP Formation
The inherent reactivity of the acryloyl polymerizable end group of AUPDS certainly has an influence on the surfmer distribution on the surface of the particles post polymerization, this could be mainly due to different reactivity ratios among the monomers [24]. Ideally, \begin{table}
\begin{tabular}{c c c c} \hline
**AUPDS (mol%)** & **Z-Average (nm)** & **PI** & **ZP (mV) a** \\ \hline \multicolumn{4}{c}{PS-_co-_AUPDS particles} \\ \hline
0.25 & - & - & - \\
0.5 & 488.3 \(\pm\) 19.4 & 0.16 \(\pm\) 0.04 & 8.7 \(\pm\) 0.5 \\
1 & 331.2 \(\pm\) 29.5 & 0.37 \(\pm\) 0.02 & \(-\)4.5 \(\pm\) 0.2 \\
2 & 90.5 \(\pm\) 1.8 & 0.13 \(\pm\) 0.01 & 35.7 \(\pm\) 0.4 \\
4 & 82.5 \(\pm\) 2.9 & 0.42 \(\pm\) 0.02 & 26.1 \(\pm\) 0.2 \\
6 & 61.3 \(\pm\) 0.3 & 0.23 \(\pm\) 0.01 & 35.4 \(\pm\) 1.7 \\
8 & 55.5 \(\pm\) 0.5 & 0.24 \(\pm\) 0.00 & 43.3 \(\pm\) 1.3 \\ \hline \end{tabular} a Measurements were performed in ultrapure water.  
\end{table} 
Table 1: _Cont._  
Figure 2: Hydrodynamic diameter distribution curves in terms of intensity (%) obtained via DLS analysis of (**a**) PS-_co-_AUPDS NPs and (**b**) PMMA-_co-_AUPDS NPs formulated using different amounts of AUPDS (in mol% relative to the dispersed phase). the surfmer should not be polymerized in the initial stages of polymerization, because this might lead to the surfmer being \"buried\" inside the particle, decreasing the amount of surfmer molecules on the surface. Hence, a lower reactivity ratio between the monomer and the surfmer facilitates that the surfmer is distributed in the interface post-polymerization [24; 56]. \(N\)-Alkyl acrylamides, for example, which we expect to have a similar co-polymerization reactivity like AUPDS, on average were reported to have a higher co-polymerization ratio with St than with MMA [57; 58; 59; 60]. With MMA, AUPDS might be incorporated to a larger extent in the final stages of polymerization, thus increasing the amount of AUPDS on the surface for PMMA-co-AUPDS particles. The opposite could happen for St, where AUPDS is incorporated to a larger extent in the earlier stages of polymerization, thus decreasing the amount of molecules on the surface. It is also pertinent to emphasize that the solubility of the monomer (St or MMA) in water should not play a significant role in these systems because in the miniEP mechanism the nucleation takes place in monomer droplets, especially when using a hydrophobic initiator (AIBN), which particularly avoids the formation of water-soluble oligomers [24; 28]. SEM micrographs of PMMA-co-AUPDS and of PS-co-AUPDS using 2 mol% of surfmer are displayed in Figure 3. It can be observed that the particles are narrowly distributed and spherically shaped. The particle diameter observed via SEM seems to be smaller when compared to the DLS data. It is often the case that polymeric particles present a decrease in size when comparing electron microscopy measurements to DLS data. This comes from the differences in samples preparation and measurement technique: SEM is performed with dried particles under low pressure, while in DLS the hydrodynamic diameter is obtained, which accounts for swelling and the solvation layer or possible particle aggregation assembly in aqueous media. In regards to the ZP, PS-co-AUPDS NPs varied with AUPDS concentration from 35 up to 43 mV. In contrast, the measured ZP values for PMMA-co-AUPDS NPs remained constant at about 44 mV with varying surfmer concentration. Considering the higher yield (at 88% for PMMA-co-AUPDS and 78% for PS-co-AUPDS), along with favorable DLS data, NPs were further synthesized using AUPDS at 2 mol% as the concentration of choice for both monomers. Among five batches using 2 mol% AUPDS, PMMA-co-AUPDS showed a Z-average size of 127.6 \(\pm\) 14.8 nm, a PI of 0.05 \(\pm\) 0.01 and a ZP of 42.2 \(\pm\) 4.1 mV. Among four batches, PS-co-AUPDS particles had an average hydrodynamic diameter of 109.3 \(\pm\) 26.4 nm, PI of 0.14 \(\pm\) 0.05, and ZP of 33.9 \(\pm\) 5.7 mV.