## 3 Results and Discussion
### Preparation of the PolyHIPE Materials
#### 3.1.2 The Emulsifier Amount  
Figure 5 showed the SEM images of polyHIPE materials prepared with different amount of emulsifier. With a higher ratio of emulsifier to the monomer (e.g., E/M 40% or 50%), the polyHIPE materials exhibited open cellular porous structures with many large open voids and interconnected \"windows\". However, a lot of the voids and windows turn into closed while using a lower amount of emulsifier (e.g., E/M 30%). The average void sizes were 23.7 \(\upmu\)m, 15.8 \(\upmu\)m and 12.0 \(\upmu\)m for the polyHIPE materials prepared with emulsifier amounts of E/M 30%, 40% and 50%, respectively, which are listed in Table 2 (Formulations 3-5).  
Figure 4: N\({}_{2}\) adsorption-desorption curves of the polyHIPE scaffolds fabricated with different W/O ratio.  
Figure 3: (**a**) Cumulative mercury intrusion traces and (**b**) Size distribution of the interconnected windows in the PolyHIPE scaffolds fabricated with different W/O ratio.  
The mercury intrusion porosimetry results in Figure 6a show that the pore volume increased from 6.15 mL/g to 9.61 mL/g while the emulsifier amount increasing. As seen from the pore size distribution results in Figure 6b, the average pore size of interconnected \"windows\" for the polyHIPE materials with 30%, 40% and 50% emulsifiers were 0.60 \(\upmu\)m, 2.56 \(\upmu\)m and 2.61 \(\upmu\)m, respectively, as listed in Table 2. From the mercury intrusion porosimetry data, the porosity for the polyHIPE materials prepared with different emulsifier amount was as high as 87.9-95.3%. Notably, the high porosity and large voids would benefit these polyHIPE materials acting as scaffolds for 3D cell culture.  
With an increase in the amount of Span 80 in the HIPE, the emulsifier is able to stabilize an increasingly large interfacial area. Thus, the average water droplet size became correspondingly smaller and the size of void decreased. At the same time, the skeletal framework (continuous phase in HIPE) of the solid poly(St-DVB) becomes progressively thinner, which causes the concomitant thinning of the continuous phase film around the aqueous droplets, which would result in an increase in the size of the window with a higher emulsifier amount.  
The nitrogen adsorption-desorption curves of the polyHIPE scaffolds were shown in Figure 7. With the increase of emulsifier amount from E/M 30% to E/M 50%, the BET surface areas increased largely from 6.3 m\({}^{2}\)/g to 24.6 m\({}^{2}\)/g, and the \(<\)Dw\(>\) decreased from 58.6 nm to 21.5 nm, as determined from the nitrogen adsorption-desorption data, which are listed in Table 2. When more Span80 is used, more surfactant molecules are located at the oil-water interface, which leads to the formation of denser and more compact interfacial films. These films can retard the passage of the water phase (the dispersed phase) through the oil phase (the continuous phase) and prevent the premature phase separation of the growing polymeric network, resulting in a larger surface area and a decrease in the pore size of \(<\)Dw\(>\).  
Figure 5: SEM images of PolyHIPE Scaffolds fabricated with emulsifier amount of (**a**) 30%, (**b**) 40% and (**c**) 50%.  
Figure 6: (**a**) Cumulative mercury intrusion traces and (**b**) Size distribution of the interconnected windows in the PolyHIPE scaffolds fabricated with different emulsifier amount.