Dawin Ute C, Lagerwall Jan P F, Giesselmann Frank
Universiat Stuttgart, Institute of Physical Chemistry, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
J Phys Chem B. 2009 Aug 20;113(33):11414-20. doi: 10.1021/jp9017772.
We investigated the electrolyte effects on the stability of nematic and lamellar lyotropic liquid crystalline (LLC) phases formed by the simple anionic surfactant cesium pentadecafluorooctanoate (CsPFO) in water. To the lyotropic guest phase, at the constant CsPFO-mass fraction of 0.55, the series of electrolytes LiCl, NaCl, KCl, CsCl, CsI, and Cs(2)SO(4), respectively, was added at concentrations ranging from 0.5 to 2.5 mol %. With increasing electrolyte concentration two substantially different effects were observed. At low concentrations all added electrolytes caused an increase of the thermal stability of the LLC phases, favoring the lamellar phase over the nematic phase. This behavior is, at least qualitatively, understood within the packing parameter model. The extent of the stabilization clearly depends on the chemical nature of the added cation. For a given cation, however, the effect is colligative, i.e., independent of the chemical nature of the added anion. At higher salt concentrations a salting-out-like phase separation was induced. This effect is clearly ion-specific as the salting-out concentration varied for each cation following the order of the Hofmeister series for cations.
我们研究了电解质对由简单阴离子表面活性剂十五氟辛酸铯（CsPFO）在水中形成的向列相和层状溶致液晶（LLC）相稳定性的影响。对于溶致客体相，在CsPFO质量分数恒定为0.55的情况下，分别添加浓度范围为0.5至2.5 mol%的一系列电解质LiCl、NaCl、KCl、CsCl、CsI和Cs₂SO₄。随着电解质浓度的增加，观察到两种截然不同的效应。在低浓度时，所有添加的电解质都会导致LLC相的热稳定性增加，相较于向列相更有利于层状相。至少在定性上，这种行为可以在堆积参数模型中得到理解。稳定化的程度明显取决于添加阳离子的化学性质。然而，对于给定的阳离子，这种效应是依数性的，即与添加阴离子的化学性质无关。在较高盐浓度下，会诱导出类似盐析的相分离。这种效应明显具有离子特异性，因为盐析浓度因每个阳离子而异，遵循阳离子的霍夫迈斯特序列顺序。
