Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
J Phys Chem B. 2013 May 16;117(19):5868-74. doi: 10.1021/jp4022807. Epub 2013 Apr 29.
Rotational diffusion of two ionic probes, cationic rhodamine 110 (R110) and anionic fluorescein (FL), has been examined in reverse micelles formed with the triblock copolymer (EO)13-(PO)30-(EO)13 (L64), where EO and PO represent ethylene oxide and propylene oxide units, respectively, with small amounts of water in p-xylene. This study has essentially been undertaken to explore the influence of mole ratio of water to copolymer (W) as well as copolymer concentration on probe rotation. On the basis of fluorescence lifetimes and reorientation times, it has been established that both R110 and FL are located in the interfacial region of L64/water/p-xylene reverse micellar system. The average reorientation time decreases by 10-35% with an increase in W for both the probes at a given copolymer concentration. However, for a particular W, the average reorientation time increases by 10-30% as the concentration of the copolymer is enhanced. From the micellar structural parameters available in the literature, critical packing parameters have been calculated for the L64/water/p-xylene reverse micellar system, and it has been noticed that the average reorientation times of both the probes scale linearly with the critical packing parameter. In essence, the results of this study indicate that the probe mobility in the interfacial region of block copolymer reverse micelles is governed by the micellar packing.
两种离子探针，阳离子罗丹明 110（R110）和阴离子荧光素（FL）的旋转扩散已在由三嵌段共聚物（EO）13-（PO）30-（EO）13（L64）形成的反胶束中进行了研究，其中 EO 和 PO 分别代表聚氧乙烯和聚氧丙烯单元，在对二甲苯中有少量的水。这项研究主要是为了探索水与共聚物摩尔比（W）以及共聚物浓度对探针旋转的影响。基于荧光寿命和重取向时间，已经确定 R110 和 FL 都位于 L64/水/对二甲苯反胶束体系的界面区域。在给定共聚物浓度下，两种探针的平均重取向时间均随 W 的增加而降低 10-35%。然而，对于特定的 W，随着共聚物浓度的增加，平均重取向时间增加 10-30%。根据文献中提供的胶束结构参数，已经计算出了 L64/水/对二甲苯反胶束体系的临界堆积参数，并注意到两种探针的平均重取向时间与临界堆积参数呈线性关系。本质上，这项研究的结果表明，探针在嵌段共聚物反胶束界面区域的迁移率受胶束堆积的控制。
