# Emulsions Stabilized with an Electrostatic Complex of
## 3 Results and Discussion
### Scanning Electron Microscopy
Once the droplets contact with one another, the emulsifier (i.e., OC\(-\)Gel) can migrate laterally on the O/W interface, and the interface void of the emulsifier can be created; thus, coalescence among the oil droplets can take place to reduce the interfacial energy. Gelatin is flexible; thus, it would readily migrate on the interface when the droplets contact one another and the fluid is drained out of the thin film between contacting interfaces. On the other hand, Em(QCNF) increased from 11.2 to about 18 um in diameter for 20 days, and the pH value had no significant effect on the size change. Since the degree of size change was much less than that of Em(OC\(-\)Gel), it was concluded that Em(QCNF) was more stable than Em(OC\(-\)Gel) in terms of droplet size. QCNF is strongly positively charged due to the trimethyl ammonium group, and its zeta potential is greater than + 30 mV. Thus, the oil droplets of Em(QCNF) would hardly agglomerate owing to the strong repulsive force developed among the droplets, accounting for why Em(QCNF) was relatively stable. In addition, QCNF is a long nanofiber, and it would be able to sterically stabilize the oil droplets due to its long length. Furthermore, even if the droplets come in close contact with one another despite the strong inter\(-\)particular  
Figure 8: (**a**) Optical micrographs of Em(OC\(-\)Gel), Em(QCNF), and Em(QCNF/OC\(-\)Gel). (**b**) Size distributions of oil droplets of Em(OC\(-\)Gel), Em(QCNF), and Em(QCNF/OC\(-\)Gel). repulsion and the steric stabilization, QCNF would hardly migrate on the O/W interface and keep its position because it is inflexible and rigid. This would be another reason why QCNF could stabilize the oil droplets effectively. Meanwhile, Em(QCNF/OC\(-\)Gel) slightly increased from 12.3 to about 14 \(\upmu\)m in diameter for 20 days when the pH value was 7.4 and 9. The complexation between QCNF and OC\(-\)Gel took place when the pH value was greater than 5. The QCNF/OC\(-\)Gel complex was thought to act as a coat of oil droplets and prevent their coalescence. Upon complexation, both the positive charge of QCNF and the negative charge of OC\(-\)Gel would decrease because of the charge neutralization. Thus, when the pH value was 7.4 and 9, the inter\(-\)particular electrostatic repulsion would be weak, and the agglomeration of the droplets would readily take place. However, the insoluble complex would allow the droplets to avoid their coalescence because it can isolate the oil droplets from their environment just as the microcapsule wall did. This would be a reason why the oil size remained almost constant for 20 days at pH 7.4 and 9. When the pH value was 5, the emulsion was stable in terms of size for 12 days, but it somewhat increased in diameter during the remaining period of the experiment. When the pH value was 3, the droplet size did not change markedly for 12 days, but it increased dramatically from 14.2 to 33.3 \(\upmu\)m. OC\(-\)Gel is positively charged under an acidic condition (e.g., pH 3) and it can hardly complex with QCNF. Thus, they would stabilize the droplets independently and individually but not by the complexed form. Besides the positive charge of OC\(-\)Gel, the intensive positive charge of QCNF would give rise to a strong inter\(-\)particular repulsion and reduce the agglomeration and the coalescence. This may explain why the emulsion was stable for 12 days even under the condition. However, the total number of collisions among the droplets will increase with time, the O/W interface without the emulsifiers would be created, and it may cause a coalescence and an increase in droplet size, accounting for why the droplet size markedly increased during the later stage. Figure 9: _Cont._