Grant Christian D, Steege Karen E, Bunagan Michelle R, Castner Edward W
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8087, USA.
J Phys Chem B. 2005 Dec 1;109(47):22273-84. doi: 10.1021/jp053929k.
Aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO109-PPO41-PEO109) copolymers are nonionic surfactants that self-organize to form aggregate structures with increasing temperature or concentration. We have studied two concentrations over a range of temperatures so that the copolymers are in one of three microphases: unimers, micelles, or hydrogels formed from body centered cubic aggregates of micelles. Three different coumarin dyes were chosen based on their hydrophobicity so that different aggregate regions could be probed independently-water insoluble coumarin 153 (C153), hydrophobic coumarin 102 (C102), and the hydrophilic sodium carboxylate form of coumarin 343 (C343-). Fluorescence anisotropy experiments provide detailed information on the local microviscosity. C153 experiences a fourfold increase in reorientation time and hence microviscosity with increasing temperature through the microphase transition from unimers to micelles. C102 also shows an increase in microviscosity with temperature but smaller in magnitude and with the microphase transition shifted to higher temperature relative to C153. C343- shows only a slight sensitivity to the microphase transition. For any of the three coumarin probes, fluorescence anisotropies do not show any correlation with the microphase transition to form cubic hydrogels.
聚环氧乙烷-聚环氧丙烷-聚环氧乙烷（PEO109-PPO41-PEO109）水性共聚物是非离子表面活性剂，会随着温度或浓度的升高自组装形成聚集体结构。我们在一定温度范围内研究了两种浓度，以使共聚物处于三种微相之一：单分子、胶束或由胶束的体心立方聚集体形成的水凝胶。基于三种香豆素染料的疏水性选择了它们，以便能够独立探测不同的聚集体区域——水不溶性香豆素153（C153）、疏水性香豆素102（C102）以及香豆素343的亲水性羧酸钠形式（C343-）。荧光各向异性实验提供了有关局部微粘度的详细信息。随着温度升高，通过从单分子到胶束的微相转变，C153的重取向时间增加了四倍，因此微粘度也增加了四倍。C102的微粘度也随温度升高，但幅度较小，且相对于C153，微相转变温度更高。C343-对微相转变仅表现出轻微的敏感性。对于这三种香豆素探针中的任何一种，荧光各向异性与形成立方水凝胶的微相转变均无任何相关性。
