Löf David, Niemiec Anna, Schillén Karin, Loh Watson, Olofsson Gerd
Physical Chemistry 1, Chemical Center, Lund University, Lund, Sweden.
J Phys Chem B. 2007 May 31;111(21):5911-20. doi: 10.1021/jp071101n. Epub 2007 May 9.
The interaction between the nonionic surfactant C12EO6 and the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO20PO68EO20 (P123) has been investigated by means of isothermal titration and differential scanning calorimetry (DSC) as well as static and dynamic light scattering (SLS and DLS). P123 self-assembles in water into spherical micelles at ambient temperatures. At raised temperatures, the DSC data revealed a sphere-to-rod transition of the P123 micelles around 60 degrees C. C12EO6 interacts strongly with P123 micelles in aqueous solution to give mixed micelles with a critical micelle concentration (cmc) well below the cmc for pure C12EO6. The presence of C12EO6 also lowers the critical micelle temperature of P123 so aggregation starts at significantly lower temperatures. A new phenomenon was observed in the P123-C12EO6 system, namely, a well-defined sphere-to-rod transition of the mixed micelles. A visual phase study of mixtures containing 1.00 wt % P123 showed that in a narrow concentration range of C12EO6 both the sphere-to-rod transition and the liquid-liquid phase separation temperature are strongly depressed compared to the pure P123-water system. The hydrodynamic radius of spherical mixed micelles at a C12EO6/P123 molar ratio of 2.2 was estimated from DLS to be 9.1 nm, whereas it is 24.1 nm for the rodlike micelles. Furthermore, the hydrodynamic length of the rods at a molar ratio of 2.2 is in the range of 100 nm. The retarded kinetics of the shape transition was detected in titration calorimetric experiments at 40 degrees C and further studied by using time-resolved DLS and SLS. The rate of growth, which was slow (>2000 s), was found to increase with the total concentration.
通过等温滴定量热法、差示扫描量热法（DSC）以及静态和动态光散射（SLS和DLS）研究了非离子表面活性剂C12EO6与聚（环氧乙烷）-聚（环氧丙烷）-聚（环氧乙烷）三嵌段共聚物EO20PO68EO20（P123）之间的相互作用。在环境温度下，P123在水中自组装成球形胶束。在升高的温度下，DSC数据显示P123胶束在60℃左右发生从球形到棒状的转变。C12EO6在水溶液中与P123胶束强烈相互作用，形成混合胶束，其临界胶束浓度（cmc）远低于纯C12EO6的cmc。C12EO6的存在还降低了P123的临界胶束温度，因此聚集在明显更低的温度下开始。在P123-C12EO6体系中观察到一种新现象，即混合胶束发生明确的从球形到棒状的转变。对含有1.00 wt% P123的混合物进行的可视化相研究表明，与纯P123-水体系相比，在C12EO6的窄浓度范围内，从球形到棒状的转变以及液-液相分离温度都显著降低。通过DLS估计，在C12EO6/P123摩尔比为2.2时，球形混合胶束的流体力学半径为9.1 nm，而棒状胶束的流体力学半径为24.1 nm。此外，在摩尔比为2.2时，棒的流体力学长度在100 nm范围内。在40℃的滴定热分析实验中检测到形状转变的延迟动力学，并通过时间分辨DLS和SLS进一步研究。发现生长速率缓慢（>2000 s），且随总浓度增加。
