Lanthanide Ion Binding in AOT/Water/Isooctane Microemulsions
Lanthanide Ion Binding in AOT/Water/Isooctane Microemulsions
复制标题
AOT/水/异辛烷微乳液中的镧系元素离子结合
作者：
H. Burrows;M. J. Tapia
微乳液作为反应介质在生物催化1和超细粉体形成2等领域的应用越来越多，它们还在各种商业配方中得到应用。3对于由反相或反相胶束形成的微乳液，水核被表面活性剂极性头基包围，烷基链与非极性溶剂一起构成连续介质。1，4形成反胶束的一种常见的两亲物是双-2-乙基己基磺基琥珀酸钠（AOT）。虽然这通常作为其钠盐使用，但用高价离子如Mg 2+、Ca 2+、Co2+、Ni 2+、Cu 2+和Zn 2+替代Na+的兴趣越来越大。5 -11由这些形成的油包水（w/o）微乳液具有强烈依赖于抗衡离子的结构，从球形到圆柱形不等。这表明，反离子和磺酸盐头基之间的相互作用在确定结构中起着主导作用。6光谱技术，特别是荧光光谱，已被发现是研究阳离子-两亲物相互作用的良好技术。三价镧系元素离子已被广泛用于进行光谱研究，因为它们具有明确的发光并且可以同晶取代不具有光谱活性的Ca（II）和Zn（II）。12，13此外，Gd（III）可以作为电子顺磁共振探针。发光14 -16和小角中子散射（SANS）16先前已被应用于Ln（AOT）3微乳液的研究，其中Ln）Tb、Eu和Nd。SANS测量结果表明存在球形反胶束。16在最近的出版物中，我们重点研究了阳离子与表面活性剂（十二烷基硫酸钠（SDS）胶束）17和聚合物（聚乙烯磺酸钠，PVS）18的相互作用，如Ce（III）向Tb（III）的能量转移或Gd（III）EPR所示。我们报告这些研究的扩展到三价镧系元素在钠AOT/水/异辛烷w/o微乳液中的行为。与以前的研究一样，我们的目标是使用发光和EPR光谱来观察镧系元素阳离子与带负电荷的表面活性剂表面的相互作用，并观察这如何影响它们的流动性。
Microemulsions are finding increasing use as reaction media in areas such as biological catalysis1 and ultrafine powder formation,2 and they have also found applications invariouscommercial formulations.3 Withmicroemulsions formed from inverted or reversed micelles, a water core is surrounded by the surfactant polar headgroups, and the alkyl chains together with a nonpolar solvent make up the continuous medium.1,4 One common amphiphile that forms inverted micelles is sodium bis-2-ethylhexylsulfosuccinate (AOT). Although this has normally been used as its sodium salt, there is increasing interest in replacement of Na+ by higher valent ions such as Mg2+, Ca2+, Co2+, Ni2+, Cu2+, and Zn2+.5-11 Water-in-oil (w/o) microemulsions formed from these have structures which are strongly dependent on the counterions, varying from spherical to cylindrical. It is suggested that the interaction between the counterion and the sulfonate headgroup plays a dominant role in determining structure.6 Spectroscopic techniques, including in particular fluorescence spectroscopy, have been found to be good techniques for studying cation-amphiphile interactions. Trivalent lanthanide ions have been widely used to carry out spectroscopic studies because they have well defined luminescence and can isomorphously substitute Ca(II) and Zn(II), which are not spectroscopically active.12,13 In addition, Gd(III) can act as an electron paramagnetic resonance probe. Luminescence14-16 and small angle neutron scattering (SANS)16 have previously been applied to the study of Ln(AOT)3 microemulsions where Ln ) Tb, Eu, and Nd. From the SANS measurements it has been shown that spherical reversed micelles are present.16 In recent publications, we have focused on the study of interaction of cations with both surfactants (sodium dodecyl sulfate (SDS) micelles)17 and polymers (sodium poly(vinyl sulfonate), PVS)18 as seen by energy transfer from Ce(III) to Tb(III) or by Gd(III) EPR. We report the extension of these studies to the behavior of trivalent lanthanides in sodium AOT/water/isooctane w/o microemulsions. As with the previous studies, our objective is to use luminescence and EPR spectroscopy to look at the interactions of lanthanide cations with the negatively charged surfactant surface and to see how this affects their mobility.