Extensive atomistic molecular dynamics (MD) simulations employing a polarizable force field have been conducted to study hydrated anion exchange membranes comprised of a poly(p-phenylene oxide) (PPO) homopolymer functionalized with quaternary ammonium cationic side groups and hydroxide anions. Representative membranes with different cationic structures have been investigated to study correlations between polymer architecture, morphology and transport properties of hydrated membranes. Specifically, hydrated polymers with five different quaternary ammonium cationic groups (R₁: –CH₃, R₂: –C₂H₅, R₃: –C₃H₇, R₄: –C₆H₁₃ and R₅: –C₄H₈OCH₃) and degree of functionalization of 50% were investigated at three hydration levels (λ = N_water/N_cation = 5, 10 and 17). Effects of the polymer structure on the distribution of water-rich domains and dynamic relaxations were systematically investigated to uncover the complex interplay between the degree of hydrophobicity/hydrophilicity of the cationic groups, morphology, connectivity of water domains, and the hydroxide transport mechanisms. Structural and dynamical analysis indicates that the bottlenecks, formed between the water-rich domains, create a substantial free energy barrier for hydroxide transport associated with the partial loss of anion hydration structure. The energy penalty associated with the loss of the hydration structure hinders the vehicular transport of the hydroxide anion. The optimal structure of functionalized homopolymer chains should be sufficiently hydrophobic to create nanophase segregation and form an interconnected network of water channels with a minimal amount of narrow bottlenecks that inhibit the vehicular motion of hydrated anions. We demonstrate that utilization of asymmetrically modified cationic groups is a promising route to achieve the desired water channel morphology at low hydration levels.

中文翻译：

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阳离子基团在水合季铵盐官能化聚对苯撑氧阴离子交换膜中结构和动力学相关性上的作用†

已经进行了利用可极化力场的广泛的原子分子动力学（MD）模拟，以研究水合阴离子交换膜，该膜包含由季铵盐阳离子侧基和氢氧根阴离子官能化的聚对苯醚（PPO）均聚物。已经研究了具有不同阳离子结构的代表性膜，以研究水合物膜的聚合物结构，形态和传输特性之间的相关性。具体而言，具有五个不同的季铵阳离子基团（R ₁：–CH ₃，R ₂：–C ₂ H ₅，R ₃：–C ₃ H ₇，R在三个水合水平（ λ = N_水/ N_{阳离子）下}研究了₄：–C ₆ H ₁₃和R ₅：–C ₄ H ₈ OCH ₃）和官能度为50％= 5、10和17）。系统地研究了聚合物结构对富水域分布和动态弛豫的影响，以揭示阳离子基团的疏水性/亲水性程度，形态，水域的连通性和氢氧化物传输机制之间的复杂相互作用。结构和动力学分析表明，在富水域之间形成的瓶颈为与阴离子水合结构的部分损失相关的氢氧化物传输创建了一个实质性的自由能垒。与水合结构的损失相关的能量损失阻碍了氢氧根阴离子的车辆运输。官能化的均聚物链的最佳结构应具有足够的疏水性，以形成纳米相分离并形成水通道的互连网络，并具有最小量的抑制水合阴离子运动的窄瓶颈。我们证明利用不对称修饰的阳离子基团是在低水合水平下实现所需水通道形态的有前途的途径。