Department of Chemical and Biomolecular Engineering, University of California-Berkeley, Berkeley, California 94720, USA.
Soft Matter. 2018 Apr 18;14(15):2789-2795. doi: 10.1039/c8sm00175h.
It is known that the addition of salts to symmetric block copolymers leads to stabilization of ordered phases and an increase in domain spacing; both trends are consistent with an increase in the effective Flory-Huggins interaction parameter between the blocks, χ. In this work, we show that the addition of salt to a disordered asymmetric block copolymer first leads to the formation of coexisting ordered phases which give way to a reentrant disordered phase at a higher salt concentration. The coexisting phases are both body centered cubic (BCC) with different domain spacings, stabilized by partitioning of the salt. Further increase in salt concentration results in yet another disorder-to-order transition; hexagonally packed cylinders are obtained in the high salt concentration limit. The coexisting phases formed at intermediate salt concentration, elucidated by electron tomography, showed the absence of macroscopic regions with distinct BCC lattices. A different asymmetric block copolymer with composition in the vicinity of the sample described above only showed only a single disorder-to-order transition. However, the dependence of domain spacing on salt concentration was distinctly non-monotonic, and similar to that of the sample with the reentrant phase behavior. This dependence appears to be an announcement of reentrant phase transitions in asymmetric block copolymer electrolytes. These results cannot be mapped on to the traditional theory of block copolymer electrolyte self-assembly based on an effective χ.
已知向对称嵌段共聚物中添加盐会导致有序相稳定和畴间距增加；这两种趋势都与嵌段之间有效 Flory-Huggins 相互作用参数 χ 的增加一致。在这项工作中，我们表明，向无序非对称嵌段共聚物中添加盐首先会导致共存有序相的形成，而在更高的盐浓度下会导致再入无序相。共存相都是体心立方 (BCC)，具有不同的畴间距，由盐的分配稳定。进一步增加盐浓度会导致另一个无序到有序的转变；在高盐浓度极限下获得六边形密堆积圆柱。通过电子断层扫描阐明的中间盐浓度下形成的共存相表明不存在具有明显 BCC 晶格的宏观区域。具有上述样品附近组成的不同非对称嵌段共聚物仅显示出单一的无序到有序转变。然而，畴间距对盐浓度的依赖性明显是非单调的，与具有再入相行为的样品相似。这种依赖性似乎预示着非对称嵌段共聚物电解质中再入相转变的出现。这些结果不能映射到基于有效 χ 的传统嵌段共聚物电解质自组装理论上。
