1. Introduction
A reverse micelle is formed by self-assembly of surfactant molecules in a nonpolar solvent, and becomes a nanometer-scale spherical cage filled with water, as shown in Fig. 1 [1]. Reverse micelles are suitable for the study of confined water because their size can be controlled by adjusting the water-surfactant molar ratio w0 (=[water] / [surfactant]) [1–5]; the size increases with w0. Accordingly, the structure and dynamics of water in reverse micelles have been extensively studied through various experimental methods, and these studies have revealed that the water's features are quite different from those of liquid water and depend on the size of the reverse micelles [1–19]. On the other hand, reverse micelles are considered good models of cells, because biomolecules, such as proteins and DNA, can be dissolved in them [2,20–23]. Water plays an important role in the function of biomolecules, and the condition of water in cells is different from that in a dilute aqueous solution of biomolecules. Therefore, studies of water confined in reverse micelles can provide basic information on water's biological function in cells.
Considerable attention has been focused on supercooled water for the past several decades, since the discovery that the thermodynamic properties of water, such as the isobaric specific heat and thermal expansion, appear to diverge at 228 K [24]. Several hypotheses were proposed to explain a number of anomalous properties of water in a
E-mail address: murakami.hiroshi@jaea.go.jp.
http://dx.doi.org/10.1016/j.molliq.2015.03.015 0167-7322/© 2015 Elsevier B.V. All rights reserved.