Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States.
ACS Macro Lett. 2021 May 18;10(5):545-550. doi: 10.1021/acsmacrolett.1c00107. Epub 2021 Apr 20.
The spontaneous ordering of block polymers doped with ions is affected by both selective solvation and long-range Coulombic interaction. The mean-field treatment was recently shown to overestimate the solvation-induced ordering, requiring a large solvation radius to fit experimental phase diagrams, which may be relieved by including composition fluctuations. Treating the composition fluctuations in such systems is challenging because of the need of resolving heterogeneous dielectric profile that couples with the ordering itself. Starting from a minimal model, we develop a Landau-Brazovskiĭ expansion for the free energy of salt-doped block polymer near the ordering transition. It is found that the wavelength for typical composition fluctuations first decreases with salt doping, due to Coulombic interaction, then increases due to ionic solvation. Two mechanisms that weaken the solvation-enhanced ordering are identified: the Brazovskiĭ-type composition fluctuation that stabilizes disordered phase, and the coupling between mismatch in dispersion interaction and the dielectric permittivity through monomeric polarizability.
离子掺杂嵌段聚合物的自发有序化受到选择性溶剂化和长程库仑相互作用的影响。最近的平均场处理表明，它高估了溶剂化诱导的有序化，需要一个大的溶剂化半径来拟合实验相图，这可能通过包含组成波动来缓解。由于需要解析与有序化本身耦合的不均匀介电轮廓，因此在这种系统中处理组成波动具有挑战性。从一个最小模型出发，我们为盐掺杂嵌段聚合物在有序化转变附近的自由能发展了一个朗道-布拉格斯基（Landau-Brazovskii）展开。结果发现，典型组成波动的波长首先由于库仑相互作用随着盐掺杂而减小，然后由于离子溶剂化而增加。确定了两种削弱溶剂增强有序化的机制：布拉索夫斯基型（Brazovskii-type）组成波动稳定无序相，以及分散相互作用和单体极化率之间的介电常数不匹配之间的耦合。
