# Phase Behavior and Rheological Properties of AES/CAPB/H\({}_{2}\)O Ternary System
## 3 Results and Discussion
### Viscosity Distribution of AES/CAPB/H\({}_{2}\)O Ternary System  
To reveal the relationship between phases and viscosity, the viscosity distribution of the AES/CAPB/H\({}_{2}\)O system is shown in Figure 5. It can be seen that the whole phase diagram is divided into four color regions: (1) Green. Viscosity: <10 Pa s; (2) Yellow. Viscosity range: 10-100 Pa s; (3) Pink. Viscosity range: 100-200 Pa s; and (4) Blue. Viscosity: >200 Pa s.  
Among all three phases, the L\({}_{1}\) phase has the lowest viscosity and is partially below 10 Pa s, which means it has excellent fluidity. For the L\(\alpha\) phase, a part has a viscosity between 10 to 100 Pa-s with good fluidity, while the part adjacent to the H\({}_{1}\) phase has a viscosity above 200 Pa-s with poor fluidity. In addition, the whole H\({}_{1}\) phase has a very high viscosity greater than 200 Pa-s with poor fluidity. Interestingly, there are only a few areas in the viscosity range of 100-200 Pa-s (pink), located in the transition region (L\({}_{1}\)\(\rightarrow\) H\({}_{1}\)) adjacent to the H\({}_{1}\) phase. This is mainly due to the rapid increase in viscosity during the transition from the L\({}_{1}\) phase to the H\({}_{1}\) phase. Therefore, the L\({}_{1}\) phase may have good application potential due to its good fluidity and low concentration of active substances. Viscosity has an important impact on many aspects of practical applications, such as energy consumption, the diffusion rate of additives, and user experience. Since there is a significant difference in the viscosity of sample \(\gamma\) and sample \(\delta\), the impact of CAPB (38%) proportion on the viscosity of the AES/CAPB/H\({}_{2}\)O system (12 wt.% AES (70%)) was further investigated as shown in Figure 6a. The viscosity of the AES/CAPB/H\({}_{2}\)O system showed an upward trend as the weight percentage of CAPB (38%) increased, but there was no significant change in the CAPB (38%) range of 8-12 wt.%. Additionally, it is known that salts, such as sodium chloride, also have an impact on the viscosity of the AES system [37; 38]. Based on the results in Figure 6a, the low viscosity sample (12 wt.% AES (70%); 9 wt.% CAPB (38%); 71 wt.% H\({}_{2}\)O) was chosen as a representative sample for investigating the effect of salt concentration on the viscosity of the AES/CAPB/H\({}_{2}\)O system, and 12 wt.% AES (70%) was used as a control sample (CAPB-free). Interestingly, it can be seen from Figure 6b that as the NaCl concentration increased, the viscosity of the control sample (CAPB-free) increased in the NaCl concentration range of 1-7 wt.% and then started to decrease, while the viscosity of the representative sample  
Figure 6: The effect of the weight percentage of (**a**) CAPB (38%) and (**b**) salts on the viscosity of the AES/CAPB/H\({}_{2}\)O system. Viscosities are expressed as means \(\pm\) SD of three measurements. (with 9 wt.% CAPB (38%)) increased in the NaCl concentration range of 1-4 wt.% and then started to decrease. Moreover, it is worth pointing out that at low NaCl concentrations, the thickening effect of NaCl on the representative sample (with 9 wt.% CAPB (38%)) is significantly better than the control sample (CAPB-free). Therefore, salts and CAPB may have a synergistic effect on increasing the viscosity of the AES/CAPB/H\({}_{2}\)O system. As a practical application, in addition to NaCl, disodium editate dihydrate (EDTA-2 Na) and citric acid are often added to the AES/CAPB/H\({}_{2}\)O system as chelating agents and pH adjusters, respectively. Thus, a basic formula (AES (70%): 12 wt.%, NaCl: 1.2 wt.%, EDTA-2 Na: 0.10 wt.%, and citric acid: 0.15 wt.%) was adopted to further study the effect of the weight percentage of CAPB (38%) on the viscosity of the AES/CAPB/H\({}_{2}\)O system. Compared to the salt-free AES/CAPB/H\({}_{2}\)O system (Figure 5(a)), the salt-containing formula exhibited significantly higher viscosity in the CAPB (38%) range of 8-12 wt.%, with a sharp increase in viscosity at 10 wt.% CAPB (38%).