3.2.1. Surface Tension

Because ethanol and water are miscible, the surface tension at different volume fractions of ethanol was measured using a surface tension meter. Different volumes of ethanol

and water were added to 40 mL headspace bottles and mixed well. The surface tension of the mixtures was measured at room temperature (20 ◦C). Reagents were added as shown in Table 2.

**Table 1.** List of alcohols used in this study.


**Table 2.** Specific plan of reagent addition.


A total of 3 × 32 mL of ultrapure water was added into three 40 mL headspace bottles separately, followed by 8 mL of n-butanol, n-amyl alcohol, and n-heptanol. The samples were placed in a shaker for 24 h, and the speed of the shaker was set at 180 rpm/min. The headspace bottles were left to stand for 30 min, and then samples were extracted with 5 mL syringes to measure the surface tension by using a surface tension meter. Each experiment was performed in triplicate to avoid experimental errors.
