**4. Results and Discussion**

## *4.1. Effect of Alcohol on Surface Tension*

After adding different volumes of ethanol, the surface tension of the mixture system gradually decreased, with surface tension values of 72.6 mN/m, 22.3 mN/m, and 30 mN/m at 0, 1, and 0.3 volume fractions of ethanol, respectively (Figure 3). Thus, when the volume of ethanol was >0.3 mL, the surface tension of the system significantly reduced, indicating that ethanol can reduce the surface tension of the solution and thus can be used as a surfactant. The optimal ratio of ethanol was 0.3.

**Figure 3.** Change curve of surface tension under different ethanol volume fractions.

Figure 4 shows the surface tension of different alcohol–water mixtures. N-butanol, n-pentanol, and n-heptanol can greatly reduce the surface tension of the solution, reducing the surface tension of the mixture to below 30 mN/m. The surface tension of the mixed system was almost equal to that of pure alcohol, thereby proving that alcohol is a good agent for reducing surface tension.

**Figure 4.** Surface tension of different alcohol–water systems, and the volume fraction of alcohol was 0.2.
