## 3 Result and Discussion  
### Establishment of the ATPS  
When the reverse micelles absorbed the water to form a water channel, the phase boundary, which the stabilizer could not absorb on, was lost, and the aggregation occurred. If the water phase inside and outside the channel formed the ATPS, a new boundary would be rebuilt to allow the stabilizer to adsorb, and the aggregation might decrease and even disappear (Figure 2).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Materials of continuous phase**} & \multicolumn{2}{c}{**Weight (g)**} & \multirow{2}{*}{**Materials of dispersed phase**} & \multirow{2}{*}{**Weight (g)**} \\ \cline{2-2} \cline{4-4}  & **First step** & & & **Second step** \\ \hline PVA & 0.2–1.6 & 0.5–4.0 & ST & 3.0 \\ Water & 17.0–19.5 & 68.0–78.0 & DVB & 1.0 \\ PEG(M\({}_{w}\) = 2,000, 6,000 and 20,000) & 0–0.6 & 0–3.0 & HD & 0.4 \\ Dextran & 0–0.6 & 0–3.0 & Span 80 & 2.0–2.4 \\ Ammonium sulfate & 0–2.0 & 0–8.0 & BPO & 0.8 \\ NaCl & 0–2.0 & 0–8.0 & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: The recipe for microspheres preparation.  
Some factors could influence the properties of the ATPS. The materials were the most significant factor. Common materials to establish the ATPS have two types: polymer-salt and polymer-polymer. Comparing the two types, the polymer-salt type usually had a high salt concentration in one phase. High ionic concentration would make the stabilizer coagulation in our experiment. Thus, the polymer-polymer ATPS became a better choice for preparing the gigaporous particles.  
For the polymer-polymer ATPS, PEG/dextran or PEG/PVA was chosen. Because PVA is the original component (stabilizer) of the polymerization system, it is more suitable to select PVA than dextran. Another reason is that PVA is much cheaper than dextran when taking into account the cost of production. The molecular weight of PEG was chosen from three different molecular weights (\(M_{\mathrm{w}}\) = 2000, 6000 and 20,000). Higher molecular weight led to high viscosity of the water phase; meanwhile, it also formed the ATPS with less concentration. In consideration of the PVA concentration to the reaction, the final ATPS component is PEG 20,000 and PVA 217. These two polymers could form the ATPS with an appropriate concentration and a suitable viscosity.  
After choosing the suitable materials, we began to draw the phase diagram. This diagram would provide important guidance in selecting suitable content for the ATPS used in preparing the particle. The temperature for making the ATPS phase diagram is a question that needs to be considered. At room temperature, the swelling step proceed and the boundary lost, and at the polymerization temperature (85 \({}^{\circ}\)C) was the time of aggregation. By comparing the phase diagrams made under two different temperatures, we found there was little difference. Therefore, the phase diagram of the PEG/PVA ATPS in 85 \({}^{\circ}\)C was chosen for further application (Figure 3). Through this diagram, the concentration and the volume of each phase could be ensured.  
Figure 3: Phase diagram of the polyethylene glycol/polyvinyl alcohol (PEG/PVA) ATPS in 85 \({}^{\circ}\)C (A: binodal line; B: tie-lines; C: the concentration ratio chosen in the research).  
Figure 2: The schematic photographs of boundary loss (**a**) and boundary rebuild (**b**).