Abstract In this paper a promising approach to implement the hydrolysis/condensation of tetraethoxysilane (TEOS) inside Nafion membrane using supercritical carbon dioxide as a solvent is suggested. Since sc CO 2 is a non-polar fluid, TEOS transport towards the hydrophilic channels of the Nafion should occur mostly through hydrophobic fluorinated domains of the Nafion swollen in CO 2 . Therefore, unlike using conventional more polar liquid solvents for TEOS, silica phase growing in the channels does not block the transport of the precursor, which impregnates the polymer matrix uniformly. As a result, silica nanoparticles having size in the range from 2 to 5 nm are formed inside the Nafion membranes. The methanol permeability is decreased from 16 × 10 -7 cm 2 /s for pristine membranes to about 9 × 10 -7 cm 2 /s for the modified ones, while the proton conductivity is not affected by the silica incorporation. Thermomechanical analysis revealed that water retention at elevated temperatures is improved by the silica incorporation. Yet, the general water uptake is reduced in comparison to the pristine samples. These results have been interpreted as an evidence for advanced performance of the composite films at high temperatures or at low humidity conditions.

中文翻译：

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在超临界二氧化碳中用二氧化硅纳米粒子改性 Nafion 用于电化学应用

摘要 本文提出了一种使用超临界二氧化碳作为溶剂在 Nafion 膜内实现四乙氧基硅烷 (TEOS) 水解/缩合的有前景的方法。由于 sc CO 2 是非极性流体，TEOS 向 Nafion 的亲水通道的传输应该主要通过在 CO 2 中溶胀的 Nafion 的疏水氟化域发生。因此，与对 TEOS 使用传统的极性更大的液体溶剂不同，在通道中生长的二氧化硅相不会阻止前体的传输，从而均匀地浸渍聚合物基质。结果，在 Nafion 膜内部形成了尺寸在 2 到 5 nm 范围内的二氧化硅纳米粒子。甲醇渗透率从原始膜的 16 × 10 -7 cm 2 /s 降低到改性膜的约 9 × 10 -7 cm 2 /s，而质子电导率不受二氧化硅掺入的影响。热机械分析表明，在高温下的保水性通过加入二氧化硅而得到改善。然而，与原始样品相比，一般的吸水量减少了。这些结果已被解释为复合薄膜在高温或低湿度条件下具有先进性能的证据。