recently, they have presented a resonance structure in the THz absorption spectrum of water in the reverse micelle using a core–shell dielectric model [14].
As described above, extensive studies of reverse micelles demonstrate that the properties of the confined water approach those of liquid water as the size of the reverse micelles increases, but that they do not agree with the properties of liquid water even at large reverse micelles of over a 10-nm diameter. This raises the question whether or not the properties of the confined water agree with those of liquid water when the confined water is free from the confinement of reverse micelles. We will address the question using the water shedding from reverse micelles in the present study.
Simorellis and co-workers have shown that water shedding from AOT reverse micelles occurs at low temperatures, as shown in Fig. 1 [15]. Other studies have reported that the temperature-dependent results of the reverse micelle in low temperature ranges are well explained in terms of this water shedding [16,17]. Furthermore, it has been shown that water extracted from the reverse micelle at small w0 values is a promising candidate for studying supercooled water because it is free from interactions with the cage in the temperature range, including the temperature of the thermodynamic singularity (~228 K) [17]. However, the manner in which the dynamic behavior of the water in the reverse micellar solution changes before and after the water shedding and whether it is like liquid water after the water shedding or not have never been examined. Such studies are needed for the studies of supercooled water using reverse micelles. The temperature at which the water shedding occurs is considered to increase with the size of the reverse micelles [16,17]. Therefore, there is a possibility that the water shedding arises above the melting point of water for large reverse micelles. If this is achieved, we can compare the temperature behavior of the THz dynamics of the water before and after the water shedding with that of liquid water.
The purpose of the present study is to examine the picosecond collective motion of water in AOT reverse micellar solutions before and after the water shedding. A reverse micelle with a large aqueous cavity is used to study the properties of bulk-like water in reverse micelles and to achieve water shedding at temperatures near room temperature. We have made temperature-dependent measurements of dynamic light scattering (DLS) to determine the temperature at which the water shedding arises. Furthermore, THz time-domain spectroscopy (THz-TDS) of water in the reverse micellar solution has been performed in the temperature range from 277 K to 295 K, wherein the water shedding occurs.