Kravchenko Vitaly S, Potemkin Igor I
Physics Department, Lomonosov Moscow State University , Moscow 119991, Russian Federation.
DWI - Leibniz Institute for Interactive Materials , Aachen 52056, Germany.
J Phys Chem B. 2016 Dec 1;120(47):12211-12217. doi: 10.1021/acs.jpcb.6b10120. Epub 2016 Nov 21.
We performed computer simulations to reveal a difference in internal structures of micelles formed by AB gradient copolymers and equivalent diblock copolymers in a selective solvent. In contrast to distinct core-shell structure of the diblock copolymer micelles (DCM), the soluble and insoluble monomer units are less segregated in the gradient copolymer micelles (GCM). Furthermore, the concentration of the soluble units in the GCM has a maximum at the core-corona interface. The maximum is a consequence of loop formation near the interface due to the broad distribution of the insoluble units along the chain and their assembly into the core of the micelle. As a result, the interfacial area per one gradient copolymer chain is larger than the area of the diblock copolymer, and the aggregation number of the GCM is smaller. Worsening of the solvent quality (increase of attraction between the insoluble groups) enlarges the aggregation number of the DCM. On the contrary, the aggregation number of the GCM practically does not change. Furthermore, the corona of the GCM becomes less swollen because more and more insoluble units join to the core and aggregate in the corona upon solvent worsening. In other words, the GCM become smaller. Such behavior is known as a "reel in" effect detected for gradient copolymer micelles at temperature elevation.39.
我们进行了计算机模拟，以揭示在选择性溶剂中由AB梯度共聚物和等效二嵌段共聚物形成的胶束内部结构的差异。与二嵌段共聚物胶束（DCM）明显的核壳结构不同，梯度共聚物胶束（GCM）中可溶和不可溶单体单元的分离程度较低。此外，GCM中可溶单元的浓度在核-冠界面处有一个最大值。该最大值是由于不可溶单元沿链的广泛分布及其组装成胶束核心而在界面附近形成环的结果。因此，每条梯度共聚物链的界面面积大于二嵌段共聚物的面积，并且GCM的聚集数较小。溶剂质量变差（不可溶基团之间吸引力增加）会增大DCM的聚集数。相反，GCM的聚集数实际上没有变化。此外，随着溶剂变差，越来越多的不可溶单元加入核心并在冠层中聚集，GCM的冠层膨胀程度降低。换句话说，GCM变小。这种行为被称为在温度升高时梯度共聚物胶束检测到的“卷入”效应。39
