Clouding behaviour in surfactant systems

Communication: Salt-induced water orientation at a surface of non-ionic surfactant in relation to a mechanism of Hofmeister effect

“…1 One of examples is the clouding phenomenon of micelles of nonionic surfactant or nonionic polymers. 2,3 With increasing temperature, the aggregation occurs in aqueous solutions inspite of the decreased translational entropy of the colloids. This has been explained by the dehydration of the colloids.…”

“…11 In contrast to the charged colloids, for which the electrostatic interaction dominates their aggregation/dispersion, the effect of the heterogeneity of water, in principle, becomes obvious in neutrally charged colloids. 2,3,9,14 Unfortunately, due to the lack of suitable experimental methods, the hydration states of the neutrally charged colloids and the effect of ions on them have long remained unexplored. In 2009, the molecular orientation of the interfacial water around surfactant monolayers had been reported in detail on the basis of heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy, which enables us to obtain the phase of the second-order nonlinear susceptibility, χ (2) .…”

“…2,3,9,14 Unfortunately, due to the lack of suitable experimental methods, the hydration states of the neutrally charged colloids and the effect of ions on them have long remained unexplored. In 2009, the molecular orientation of the interfacial water around surfactant monolayers had been reported in detail on the basis of heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy, which enables us to obtain the phase of the second-order nonlinear susceptibility, χ (2) . 15 Since then, an increasing number of reports have been published on the interfacial properties of water molecules such as the molecular orientation and hydrogen-bonding network at the surfaces of ionic surfactants or zwitterionic lipids using this technique.…”

“…Some details specific to this study including data manipulation procedure are given in the supplementary material. 20 The χ (2) has a non-zero value only when the system has a broken inversion-symmetry, i.e., when some transition (2) reflect the direction and the strength of the orientation, respectively. [15][16][17][18] For measurements of electrostatic surface potentials (ζ potentials), monomyristolein was mixed with 100 mM of each saline solution so as to be about 0.1 mM.…”

“…[11][12][13] Effect of anions is known to be stronger than that of cations. The order of anions for "water structure maker" is SO 2…”