## 3 Results and Discussion
### Influence of the Surfmer Concentration on NP Formation  
The AUPDS surfmer was used as surfactant replacement and co-monomer in the preparation of MMA and PS NPs with a surfmer feed concentration between 0.25 and 8 mol% relative to the dispersed monomer phase. Variations in the values of the hydrodynamic diameters, PI and ZP were used as parameters to evaluate particle size, distribution and stability and these results are displayed in Table 1 and Figure 2. The PI is a value (from 0 to 1) calculated from two parameters obtained from the correlation data (the DLS data cumulant analysis), where values \(\leq\)0.1, 0.1-0.2, 0.2-0.4, or \(\geq\)0.7 represent samples that are monodisperse, nearly monodisperse, mid-range and not suitable for DLS, correspondingly [48]. The ZP--or electrokinetic potential--is a qualitative measure of the potential between the electric double layer of the particles and the dispersion media and it is a well-established parameter for the evaluation of particle stability in a suspension. The obtained value brings insights into the electrostatic repulsion between particles, in which the values 0-10 mV, 10-20 mV, 20-30 mV, and \(>\)30 mV conventionally represent highly unstable, relatively stable, moderately stable, and highly stable particles, respectively [55]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**AUPDS (mol\%)** & **Z-Average (nm)** & **PI** & **ZP (mV) a** \\ \hline \multicolumn{4}{c}{PMMA-co-AUPDS particles} \\ \hline
0.25 & - & - & - \\
0.5 & - & - & - \\
1 & - & - & - \\
2 & \(118.5\pm 0.3\) & \(0.05\pm 0.00\) & \(40.1\pm 0.8\) \\
3 & \(134.0\pm 0.2\) & \(0.10\pm 0.00\) & \(42.8\pm 1.2\) \\
4 & \(124.5\pm 0.1\) & \(0.07\pm 0.02\) & \(45.9\pm 1.1\) \\
6 & \(129.0\pm 1.1\) & \(0.08\pm 0.02\) & \(42.9\pm 0.9\) \\
8 & \(150.0\pm 1.1\) & \(0.13\pm 0.01\) & \(44.0\pm 0.2\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Z-average hydrodynamic diameters, polydispersity index (PI), and zeta potential (ZP) values obtained for PMMA-co-AUPDS and for PS-co-AUPDS particles with different amounts of AUPDS. Values are presented in average \(\pm\) standard deviation (\(n=3\)). When using formulations with low surfmer concentrations of 0.5 and 1 mol% AUPDS, PS particles presented an increased PI (0.16 and 0.37) and a low ZP (+8.7 to \(-\)4.5 mV), whereas PMMA particles were not even produced at this range. The reason for that is because this amount of surfmer was not enough to stabilize the mini-emulsion before polymerization. Our results are in agreement with the results obtained by [PERSON] et al. for SDS as the surfactant for the miniEP of St: when using less than 1 mol% of surfactant, there is just not enough coverage of the monomer droplets to stabilize the system [54]. After the minimum concentration is reached and a stable mini-emulsion is formed, it is possible to produce stable droplets with as little as 10-30% surface area coverage using miniEP systems [51]. Variation in the AUPDS concentrations \(\geq\) 2 mol% yielded monodisperse PMMA-co-AUPDS particles with hydrodynamic diameters fluctuating between 118 nm and 150 nm and PI below 0.13. On the other hand, PS-_co-_AUPDS particles presented a slight decrease in the hydrodynamic diameter from 90 to 55 nm with increasing surfmer amounts \(\geq\) 2 mol%, but size distributions were broader when using more than 4 mol% AUPDS (PI \(\geq\) 0.23). An increase in the surfactant concentration usually leads to a decrease in the particle size due to the increase in the number of droplets in the mini-emulsion, provided that the droplets are covered with enough surfactant [50; 53]. This was observed for PS-_co-_AUPDS, but not for PMMA-_co-_AUPDS particles. In both mini-emulsions, the AUPDS acts as a stabilizer, replacing the use of surfactant, while also being a co-monomer to St or MMA.