Makromolekulare Chemie II and Bayreuther Zentrum für Kolloide und Grenzflächen, Universität Bayreuth, D-95440 Bayreuth, Germany.
Langmuir. 2010 Jul 20;26(14):12237-46. doi: 10.1021/la101173b.
We present a systematic investigation of the extent of compartmentalization in micelles formed by a series of bis-hydrophilic block terpolymers with two outer water-soluble segments. The corona blocks are constructed from poly(ethylene oxide) (PEO) and the thermoresponsive poly(N-isopropyl-acrylamide) (PNiPAAm). The fraction of PNiPAAm is varied to establish its influence on the supramicellar aggregation and corona phase behavior. We demonstrate that--when the collapse of PNiPAAm is triggered--a clustering of micelles into superstructures only occurs when the contour length of the thermoresponsive block is longer than that of the PEO chains. The volume fractions play a minor role. The extent of superstructure formation increases with the amount of heating cycles, pointing to a rearrangement of micelles with a mixed corona into a phase-segregated corona. The collapse of PNiPAAm is exploited to artificially raise the incompatibility and drive phase segregation. A uniform population of biphasic Janus micelles cannot be obtained. After repeated heating cycles, the mixture consists of a range of multicompartment architectures, whose patch distribution can be derived from aggregate structures found in cryo-TEM obtained at high temperature. In the last section, we relate our results to previously studied systems and attempt to derive some generalities. First, we try to answer the question of how likely it is in terms of thermodynamics to obtain truly self-assembled Janus micelles. Furthermore, our results can provide an estimation for the volume ratio or/and block lengths required in micelles composed out of two corona blocks to induce supramicellar aggregation when a hydrophilic-to-hydrophobic phase transition is triggered in one of the blocks.
我们系统地研究了一系列具有两个外亲水性段的双亲水性嵌段三聚物形成的胶束的分隔程度。冠形块由聚（氧化乙烯）（PEO）和温敏性聚（N-异丙基丙烯酰胺）（PNiPAAm）构成。改变 PNiPAAm 的分数以确定其对超胶束聚集和冠相行为的影响。我们证明，当 PNiPAAm 发生塌陷时，只有当热响应性嵌段的轮廓长度长于 PEO 链时，胶束才会聚类成超结构。体积分数的作用较小。超结构形成的程度随加热循环次数的增加而增加，表明具有混合冠的胶束重新排列成相分离的冠。PNiPAAm 的塌陷被用来人为地提高不兼容性并驱动相分离。无法获得均匀的双相 Janus 胶束群体。经过多次加热循环，混合物由一系列多隔室结构组成，其斑块分布可以从在高温下获得的低温 TEM 中找到的聚集结构推导出来。在最后一节中，我们将我们的结果与之前研究的系统进行了比较，并尝试得出一些一般性结论。首先，我们试图回答从热力学的角度来看，获得真正自组装的 Janus 胶束的可能性有多大。此外，我们的结果可以为在一个亲水 - 疏水相转变引发一个嵌段时，由两个冠形嵌段组成的胶束诱导超胶束聚集所需的体积比或/和嵌段长度提供估计。
