## 3 Results and Discussion  
### Effects of Monomer Feed Ratio  
The aim of miniemulsion copolymerization of St and AA is to increase the stability and prevent the coagulation of submicrocapsules containing functional materials in the core (phytoncide oil, in this case) by virtue of the enhanced zeta potential of submicrocapsules due to -COO\({}^{-}\) functional groups of AA. The salient feature of our current study is that miniemulsion copolymerization of St with AA yields electronically stabilized submicroapsules which can be used as carriers for the Typophilic core.  
Figure 1 shows the effects of the monomer feed ratio [AA]/[St] of miniemulsion copolymerization of St and AA on the mean particle size and zeta potential of the St/AA submicrocapsule. The particle size of the St/AA submicroparticle presents a minimum value of 392.6 nm at 0.33 of the monomer feed ratio (Figure 1a). The particle size of the St/AA submicroparticles decreased with the increase of [AA] at [AA]/[St] = 0.2-0.33 range, which was ascribed to the increased surface potential of micelles. For increased [AA]/[St] over 0.33, however, there was a steep increase in the mean particle size of the submicroparticles. As is well known, copolymerization behavior is mainly affected by the different reactivities of monomers. Compared with St, AA polymerizes vary rapidly, especially at low pH. Therefore, the increase of AA led inevitably to longer polyacrylic blocks in the copolymer formation at the particle-water interface, and increased the particle diameter. The increase in particle size with the increase in the amount of AA results in the formation of a hydrophilic swollen layer around the particle [27]. Absolute value of zeta potential (Figure 1b) increased to \(-55.2\) mV with the increases of [AA] at [AA]/[St] = 0.2-0.33 range. The decrease in the absolute zeta potential value at over [AA]/[St] = 0.33 was attributed to the particle agglomeration in the aqueous phase due to the increased hydrophilic swollen layer of the particles and resulting reduction in surface area [29; 30]. This can also be confirmed from SEM photographs presented in Figure 2. The St/AA submicroparticles prepared at [AA]/[St] = 0.5 and 1.0 showed crumpled and contorted morphology, which arose from the agglomeration of particles due to the fusion of hydrophilic swollen layers in dispersive medium.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Phase** & **Ingredients** & **Condition** \\ \hline \multirow{2}{*}{Water phase} & Distilled water & 80 mL \\ \cline{2-3}  & SDS & 0.6-1.4 \(\times\) 10\({}^{-3}\) mol \\ \hline \multirow{4}{*}{Oil phase} & Phytoncide oil & 10 g \\ \cline{2-3}  & DVB & 250 mg \\ \cline{2-3}  & \(n\)-Hexadecane & 450 mg \\ \cline{2-3}  & Monomer & 0.172 mol \\ \cline{2-3}  & (feed ratio [AA]/[St]) & (0.2-1.0) \\ \hline \multirow{2}{*}{Homogenization} & Rate & 19,000 rpm \\ \cline{2-3}  & Duration & 10 min \\ \hline \hline \end{tabular}
\end{table}
Table 1: Experimental conditions for miniemulsion copolymerization of St and AA.  
Fused morphology of St/AA submicrocapsules indicates the low thermal durability of the wall of submicrocapsules that is unable to tolerate the deposition process prior to microscopic analysis.