Li Xue, Zhang Hong, Lin Cheng, Tian Ran, Zheng Penglun, Hu Chenxing
School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China.
Civil Aircraft Fire Science and Safety Engineering Key Laboratory of Sichuan Province, Civil Aviation Flight University of China, Guanghan 618307, China.
Polymers (Basel). 2022 Dec 15;14(24):5499. doi: 10.3390/polym14245499.
With the recognition of the multiple advantages of sulfonated hydrocarbon-based polymers that possess high chemical and mechanical stability with significant low cost, we employed molecular dynamics simulation to explore the morphological effects of side chain length in sulfonated polystyrene grafted poly(arylene ether sulfone)s (SPAES) proton exchange membranes. The calculated diffusion coefficients of hydronium ions (HO) are in range of 0.61-1.15 × 10 cm/s, smaller than that of water molecules, due to the electrical attraction between the oppositely charged sulfonate group and HO. The investigation into the radial distribution functions suggests that phase segregation in the SPAES membrane is more probable with longer side chains. As the hydration level of the membranes in this study is relatively low (λ = 3), longer side chains correspond to more water molecules in the amorphous cell, which provides better solvent effects for the distribution of sulfonated side chains. The coordination number of water molecules and hydronium ions around the sulfonate group increases from 1.67 to 2.40 and from 2.45 to 5.66, respectively, with the increase in the side chain length. A significant proportion of the hydronium ions appear to be in bridging configurations coordinated by multiple sulfonate groups. The microscopic conformation of the SPAES membrane is basically unaffected by temperature during the evaluated temperature range. Thus, it can be revealed that the side chain length plays a key role in the configuration of the polymer chain and would contribute to the formation of the microphase separation morphology, which profits proton transport in the hydrophilic domains.
鉴于磺化烃基聚合物具有多种优势，如化学和机械稳定性高且成本显著低廉，我们采用分子动力学模拟来探究磺化聚苯乙烯接枝聚（亚芳基醚砜）（SPAES）质子交换膜中侧链长度对形态的影响。由于带相反电荷的磺酸根基团与水合氢离子（H₃O⁺）之间的电吸引力，计算得到的水合氢离子扩散系数在0.61 - 1.15×10⁻⁶ cm²/s范围内，小于水分子的扩散系数。对径向分布函数的研究表明，SPAES膜中侧链越长，越有可能发生相分离。由于本研究中膜的水合水平相对较低（λ = 3），较长的侧链对应着非晶胞中更多的水分子，这为磺化侧链的分布提供了更好的溶剂效应。随着侧链长度的增加，磺酸根基团周围水分子和水合氢离子的配位数分别从1.67增加到2.40以及从2.45增加到5.66。相当一部分水合氢离子似乎处于由多个磺酸根基团配位的桥连构型中。在评估的温度范围内，SPAES膜的微观构象基本不受温度影响。因此，可以看出侧链长度在聚合物链的构型中起关键作用，并有助于形成微相分离形态，这有利于质子在亲水区域的传输。
