2.2. Determination of Critical Micelle Concentration

The critical micelle concentration (CMC) for the mixture of Soluplus^®/P407 was evaluated by ultraviolet (UV) spectrophotometry as reported earlier [18]. Briefly, potassium iodide (KI, 1.0 g) and iodine (I₂, 0.5 g) were dissolved in deionized water (50 mL) to obtain a KI/I₂ solution. The KI/I₂ solution (5 μL) was added into the aqueous solution (15 mL) of Soluplus^®/P407 (mass ratio: 2:1) with polymer concentrations ranging from 0.00024 to 0.125 mg/mL. Then, the mixtures were vortexed and incubated in the dark at room temperature for 12 h. The absorbance was determined at 366 nm by UV spectrophotometer (UV759CRT, Shanghai Yoke, Shanghai, China). The CMC was determined from the onset of a sharp rise in absorbance plotted versus the logarithm of the polymer concentration.