Fig. 1. (a) Molecular formula of Igepal CO-520; n in the formula is about 5. (b) Schematic illustration of prepared reverse micelle.

Fig. 2. (a) Time-domain spectra of air reference and measured reverse micelle mixtures; (b) frequency-domain spectra of air reference and measured reverse micelle mixtures.

Fig. 3. THz complex permittivity (circle markers) of reverse micelles and fitted lines (solid lines) with proposed model.

Fig. 4. Decomposed spectra of (a)–(b) ω₀ = 5 and (c)–(d) 15 including fast water (blue solid line), bulk water (green solid line), and the background, which is determined linearly by the permittivity of ω₀ = 0 mixture (pink solid line). (a), (c) and (b), (d) represent the real and imaginary part of obtained complex permittivity, respectively. The black dashed line is the fitted line with the proposed model.

Fig. 5. (a) Obtained molar concentration of fast water (blue dashed line), bulk water (green dashed line), hydration water (red dashed line), and total water (black dashed line); (b) zoomed-in molar concentration of fast water; (c) calculated hydration water number per Igepal molecule.

Fig. 6. (a) Definition of radius of nonhydrated, hydrated, and the total water nanopool; (b) ratios of the radius of nonhydrated (blue circles and dashed line) and hydrated water (red circles and dashed line) to the radius of the total water nanopool.