W/O microemulsions prepared with sodium bis (2-ethylhexyl) sulfosuccinate (AOT) have been used to form nano particles. Properties of the particles such as the shape and size are different from those of the particles formed with aqueous solutions. One of the possible causes of the properties is peculiar properties of the water pool of W/O microemulsions. However, the relationship between the properties of the water pool and those of the particles has not been investigated. In this study, as a first step to clarify the relationship, the peculiar properties of the water pool were investigated as a function of the size of the water pool. Light water (normal water) and heavy water were used to prepare the W/O microemulsions. Polarity, supercooling point and hydrogen bonding of the water pool and bulk water (light and heavy) were measured using fluorescent probe 1-anilino-8-naphthalene sulfonate (ANS), differential scanning calorimeter (DSC) and Fourier transform infrared spectroscopy (FT-IR) respectively. It was found that polarity, supercooling point and hydrogen bonding of the water pool are lower than those of bulk water. When light water is used to prepare W/O microemulsions, those properties are uniform at the size > 7nm, whereas they gradually become lower at the size < 7nm. In the case of heavy water, such a transition of the properties are observed at the size < 5nm. These peculiar properties may be due to the interaction between sulfonate groups of AOT and water molecules at the interface of W/O microemulsions.
