PLURONIC-P105 PEO-PPO-PEO BLOCK-COPOLYMER IN AQUEOUS UREA SOLUTIONS - MICELLE FORMATION, STRUCTURE, AND MICROENVIRONMENT
PLURONIC-P105 PEO-PPO-PEO BLOCK-COPOLYMER IN AQUEOUS UREA SOLUTIONS - MICELLE FORMATION, STRUCTURE, AND MICROENVIRONMENT
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DOI：
10.1021/la00007a022
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发表时间：
1995-07-01
期刊：
影响因子：
3.9
通讯作者：
HATTON, TA
中科院分区：
文献类型：
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作者：
ALEXANDRIDIS, P;ATHANASSIOU, V;HATTON, TA
报道了尿素对聚（环氧乙烷）-嵌段-聚（环氧丙烷）-嵌段-聚（环氧乙烷）（PEO-PPO-PEO）共聚物（市售为Pluronic P105）的胶束化性质以及对胶束的结构和微环境的影响。临界胶束化浓度（CMC）和温度（CMT）值的两亲性嵌段共聚物溶解在尿素/水的混合物（尿素浓度0，1，2，和4 M），获得使用染料增溶方法和证实的数据从表面张力，密度，和荧光光谱实验。尿素增加了PEO-PPO-PEO共聚物的cmc和cmt;尿素对cmt的影响在低共聚物浓度下更明显，并且在类似于2.5%的浓度下减小。胶束形成的热力学参数在尿素的存在下，估计使用一个封闭的协会模型;胶束化的焓是积极的（吸热），并减少尿素浓度的增加。嵌段共聚物的表面活性和部分比容随尿素浓度的增加而降低，而使用动态光散射测定的共聚物胶束的流体动力学半径保持不受溶液中存在4 M尿素的影响。在共聚物溶液中的微极性在尿素/水探测作为温度的函数使用的I-1/I-3的强度比的芘振动的精细结构记录在荧光发射光谱;一个小的减少在胶束核心的微极性中观察到在尿素的存在下。在胶束内部的微粘度，估计从分子内的准分子荧光的疏水探针双（1-芘甲基）醚（dipyme），也表现出一个小的减少与尿素浓度的增加。这里提出的研究结果进行了讨论的背景下，尿素的影响的分子机制。
The effects of urea on the micellization properties of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) copolymer (commercially available as Pluronic P105) and on the structure and microenvironment of the micelles are reported. Critical micellization concentration (cmc) and temperature (cmt) values for the amphiphilic block copolymer dissolved in urea/water mixtures (urea concentration 0, 1, 2, and 4 M) were obtained using a dye solubilization method and corroborated with data from surface tension, density, and fluorescence spectroscopy experiments. Urea increased the cmc and cmt of the PEO-PPO-PEO copolymer; the effect of urea on the cmt was more pronounced at low copolymer concentrations and diminished at concentrations of similar to 2.5%. The thermodynamic parameters of micelle formation in the presence of urea were estimated using a closed association model; the enthalpy of micellization was positive (endothermic) and decreased upon increasing the urea concentration. The surface activity and the partial specific volume of the block copolymer decreased with an increase in the urea concentration, whereas the hydrodynamic radii of the copolymer micelles, determined using dynamic light scattering, remained unaffected by the presence of 4 M urea in the solution. The micropolarity in copolymer solutions in urea/water was probed as a function of temperature using the I-1/I-3 intensity ratio of the pyrene vibrational fine structure recorded in fluorescence emission spectra; a small decrease in the micropolarity of the micelle core was observed in the presence of urea. The microviscosity in the micelle interior, estimated from the intramolecular excimer fluorescence of the hydrophobic probe bis(1-pyrenylmethyl) ether (dipyme), also exhibited a small decrease with an increase in the urea concentration. The findings presented here are discussed in the context of the molecular mechanism underlying the effects of urea.