Mensharapov Ruslan M, Ivanova Nataliya A, Spasov Dmitry D, Grigoriev Sergey A, Fateev Vladimir N
National Research Center "Kurchatov Institute", 1, Akademika Kurchatova sq., 123182 Moscow, Russia.
National Research University "Moscow Power Engineering Institute", 14, Krasnokazarmennaya st., 111250 Moscow, Russia.
Polymers (Basel). 2022 Oct 18;14(20):4395. doi: 10.3390/polym14204395.
In this study, we performed small-angle X-ray scattering (SAXS) to investigate the structure of Nafion membranes. The effect of freeze/thaw (F/T) cycles (from ambient temperature down to -40 °C) on the membrane nanostructure was considered for the first time. The SAXS measurements were taken for different samples: a commercial Nafion 212 membrane swollen in water and methanol solution, and a water-swollen silica-modified membrane. The membrane structure parameters were obtained from the measured SAXS profiles using a model-dependent approach. It is shown that the average radius of water channels () decreases during F/T cycles due to changes in the membrane structure as a result of ice formation in the pore volume after freezing. The use of water-methanol solution (methanol content of 20 vol.%) for the membrane soaking prevents changes in the membrane structure during F/T cycles compared to the water-swollen membrane. Modification of the membrane surface with silica (SiO content of 20 wt.%) led to a redistribution of water in the membrane volume and resulted in a decrease in . However, for the modified membrane did not decrease with the increasing number of F/T cycles due to the involvement of SiO in the sorption of membrane water and, therefore, the prevention of ice formation.
在本研究中，我们进行了小角X射线散射（SAXS）实验以研究Nafion膜的结构。首次考虑了冻融（F/T）循环（从环境温度降至-40°C）对膜纳米结构的影响。对不同样品进行了SAXS测量：一种在水和甲醇溶液中溶胀的商用Nafion 212膜，以及一种水合溶胀的二氧化硅改性膜。使用基于模型的方法从测量的SAXS曲线中获得膜结构参数。结果表明，由于冷冻后孔体积中形成冰导致膜结构发生变化，在F/T循环过程中水道的平均半径（）减小。与水合溶胀膜相比，使用水-甲醇溶液（甲醇含量为20体积%）浸泡膜可防止在F/T循环过程中膜结构发生变化。用二氧化硅（SiO含量为20重量%）对膜表面进行改性导致膜体积内水的重新分布，并导致减小。然而，由于SiO参与膜水的吸附并因此防止了冰的形成，改性膜的不会随着F/T循环次数的增加而减小。
