Dutt G B
Radiation Chemistry & Chemical Dynamics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
J Phys Chem B. 2005 Mar 24;109(11):4923-8. doi: 10.1021/jp0453459.
Rotational diffusion of two structurally similar hydrophobic probes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been examined in aqueous solutions of poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20 triblock copolymer as a function of temperature. These studies have been carried out to explore the influence of critical micelle temperature (cmt) on probe dynamics. It has been observed that, below cmt, the anisotropy decays can be adequately described by single-exponential functions with one time constant each for DMDPP and DPP. However, above cmt, biexponential functions with two time constants are needed to satisfactorily fit the anisotropy decays. Another important observation is that both the probes rotate more rapidly below the critical micelle temperature. The dynamics of the probe molecules are akin to that in a homogeneous solution below cmt, whereas above cmt, the rotational diffusion of the probes has been accounted by the two-step model, which is usually employed to explain the results in micelles. A comparison between the microviscosities of these micelles with other nonionic micelles such as Triton X-100 and Brij-35 reveals that the internal environment of the micelles formed with the triblock copolymer is less fluid.
在聚(环氧乙烷)20 - 聚(环氧丙烷)70 - 聚(环氧乙烷)20三嵌段共聚物的水溶液中,研究了两种结构相似的疏水探针2,5 - 二甲基 - 1,4 - 二氧代 - 3,6 - 二苯基吡咯并[3,4 - c]吡咯(DMDPP)和1,4 - 二氧代 - 3,6 - 二苯基吡咯并[3,4 - c]吡咯(DPP)的旋转扩散随温度的变化。进行这些研究是为了探索临界胶束温度(cmt)对探针动力学的影响。据观察,在cmt以下,DMDPP和DPP的各向异性衰减可以分别用具有一个时间常数的单指数函数充分描述。然而,在cmt以上,需要具有两个时间常数的双指数函数才能令人满意地拟合各向异性衰减。另一个重要观察结果是,两种探针在临界胶束温度以下旋转得更快。在cmt以下,探针分子的动力学类似于在均相溶液中的动力学,而在cmt以上,探针的旋转扩散已由通常用于解释胶束中结果的两步模型来解释。将这些胶束与其他非离子胶束(如Triton X - 100和Brij - 35)的微观粘度进行比较,结果表明由三嵌段共聚物形成的胶束的内部环境流动性较小。