# Synergistic Effect and Phase Behavior of SCG-CAPB-H\({}_{2}\)O
## 3 Results and Discussion
### The Phase Behavior of SCG/CAPB System
#### 3.2.3 Mechanism of Phase Transition over SCG/CAPB/H2O System  
In order to investigate the phase transition mechanism between different phases of SCG/CAPB/H2O system, a series of samples were selected as the research objects. The mass fraction, phase state, and viscosity of each component of samples 5-10 are shown in Table 5.  
Sample 5 belongs to the region of mixed micelle-solid phase in the phase diagram. In this region, SCG has not completely dissolved, and undissolved surfactant monomers form hydrated crystals due to hydration and remain freely dispersed in the aqueous solution. Viscosity testing was conducted on the sample, revealing that the viscosity of sample 5 is approximately 100 times that of sample 6. This could be attributed to the increased relative content of CAPB in the solution. The cationic head groups of CAPB may exert strong electrostatic attraction on the anionic head groups of SCG molecules, weakening the hydrogen bonding interactions between SCG monomers and leading to the rupture of intermolecular hydrogen bonds. As a result, the electrostatic interaction attracts SCG molecules into the interior of CAPB micelles, increasing the solubility of SCG and reducing the resistance to relative sliding between hydrated crystals, thereby decreasing viscosity.  
Through POM, SAXS, and viscosity testing, it was observed that although samples 6 and 7 belong to the micellar phase, the viscosity of the solution increases with the higher relative content of CAPB. This is because at this stage, both the number and size of CAPB micelles increase, leading to an increase in relative sliding resistance between particles in the solution. When the relative content of CAPB further increases in the solution, a significant phase transition occurs from the micellar phase of sample 7 to the lamellar phase of sample 8. It is speculated that the increasing compression between micelles prevents them from maintaining their original spherical shape, and combined with the strong hydrophobic effect of SCG molecular head groups, the micelles gradually transform into a lamellar phase.  
Samples 9 and 10 were subjected to small-angle X-ray scattering, and the SAXS results are presented in Figure 7. Based on the scattering vector q corresponding to the first Bragg peak, the interlayer spacing (d) for the layered phase and the distance (d\({}_{\rm H}\)) between cylindrical layers in the hexagonal phase were calculated using (d = 2\(\pi\)/q) and (d\({}_{\rm H}\) = 4\(\pi\)/ \(\surd\)sq), respectively. The calculations yielded an interlayer spacing (d) of 5.5477 nm for sample 9 and a distance (d\({}_{\rm H}\)) between cylindrical layers of 6.0733 nm for sample 10. This indicates that with an increase in the relative content of SCG, the system transitions from a layered phase to a hexagonal phase, and the distance between the liquid crystal phases increases. This increase is speculated to be due to the stronger interactions between SCG and CAPB molecules, leading to a denser arrangement of SCG and CAPB within the cylindrical layers.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample No.** & **SCG (wt\%)** & **CAPB (wt\%)** & **H2O (wt\%)** & **Phase** & **Viscosity (Pa-S)** \\ \hline
5 & 15 & 5 & 80 & S-L\({}_{1}\) & 0.5168 \\
6 & 5 & 15 & 80 & L\({}_{1}\) & 0.0072 \\
7 & 5 & 25 & 70 & L\({}_{1}\) & 0.0176 \\
8 & 10 & 30 & 60 & L\({}_{\rm A}\) & 1.1907 \\
9 & 10 & 35 & 55 & L\({}_{\rm A}\) & 6.7612 \\
10 & 15 & 35 & 50 & H & 16.3508 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Mass fraction, phase state, and viscosity of each component of Sample 5–10.