2D-Ising-like critical behavior in mixtures of water and 3-methylpyridine including antagonistic salt or ionic surfactant

作者：Sadakane Koichiro; Iguchi Natsuki; Nagao Michihiro; Endo Hitoshi; Melnichenko Yuri B; Seto Hideki^*

来源：Soft Matter, 2011, 7(4): 1334-1340.

DOI：10.1039/c0sm00598c

The effect of an antagonistic salt on the phase behavior and nanoscale structure of a mixture of D(2)O and 3-methylpyridine was investigated by visual inspection and small-angle neutron scattering (SANS). The addition of the antagonistic salt, namely sodium tetraphenylborate (NaBPh(4)), induces the shrinking of the two-phase region in contrast to the case in which a normal (hydrophilic) salt is added. Below the phase separation point, the SANS profiles cannot be described by the Ornstein-Zernike function owing to the existence of a long-range periodic structure. With increasing salt concentration, the critical exponents change from the values of 3D-Ising and approach those of 2D-Ising. These results suggest that the concentration fluctuation of the mixture of solvents is limited to a quasi two-dimensional space by the periodic structure induced by the adding the salt. The same behaviors were also observed in mixtures composed of water, 3-methylpyridine, and ionic surfactant.

• 出版日期2011