Gas Transport Properties of Ion-irradiated Membrane with Nano-channel

本研究采用高真空装置和Baratron绝对压力计，在76 cmHg和35°C下，测量了离子辐照非对称聚酰亚胺膜的气体渗透性和选择性。采用干-湿相转化法制备了非对称聚酰亚胺膜，并对膜表面皮层进行了能量密度为1 × 10 ~（12）~ 3 × 10 ~（15）（He ~+/cm ~ 2）、能量为50 keV的离子辐照。结果表明，He ~+辐照膜的气体选择性随离子注量的增加而增加，辐照离子在皮层的能量损失深度分布对非对称膜的气体渗透性和气体选择性有显著影响，膜的气体渗透性在低注量时增加，在高注量时减小。另一方面，气体选择性随着离子注量的增加而增加。一种可能性是在离子辐照皮肤表面上形成了气体渗透空间，该空间可以提供气体分子之间高度的尺寸和形状区分，并且抑制了N_2和CH_4的渗透而不是O_2和CO_2的渗透。另一个有趣的结论是，离子辐照的皮肤层的厚度对气体渗透性和选择性有显着的影响。离子辐照膜表面层中的聚酰亚胺结构与离子能量损失量密切相关，从而决定了膜中形成的自由体积和自由体积分布，因此制备具有高气体渗透性和气体分离选择性的聚合物膜是理想的。本研究中制备的离子辐照不对称聚酰亚胺膜显示出有趣的气体渗透结果，我们认为离子辐照将是实现高气体渗透性和选择性的重要膜制备技术之一。

In this research, the gas permeance and selectivity of the asymmetric polyimide membrane irradiated by ions were measured using a high vacuum apparatus with a Baratron absolute pressure gauge at 76cmHg and 35°C. The asymmetric polyimide membranes were prepared from a dry-wet phase inversion process, and the surface skin layer on the membrane was irradiated by ions in the fluence range from lx1012 to 3x1015(He+/cm2) at 50keV. We demonstrated that the gas selectivity of the He+-irradiated membrane increased with an increase in the ion fluence and that the depth profile of the energy loss for the irradiating ions in the skin layer had a significant influence on the gas permeability and selectivity of the asymmetric membrane.The gas permeances for the membrane showed an increase at a low ion fluence and a decrease at a high ion fluence. On the other hand, the gas selectivity increased with an increase in the ion fluence. One possibility may be that the gas permeation space, which can provide a high degree of size and shape discrimination between the gas molecules, was formed on the ion-irradiated skin surface and suppressed the permeability of N_2 and CH_4 rather than that of O_2 and CO_2. Another interesting conclusion is that the thickness of the ion-irradiated skin layer had a significant influence on the gas permeability and selectivity. The polyimide structure in the ion-irradiated surface layer would be closely correlated to the amount of ion energy loss so that the structure may determine the free volume and the free volume distribution formed in the membrane.It is desirable to prepare a polymer membrane with both a high gas permeability and selectivity for gas separation. The ion-irradiated asymmetric polyimide membrane prepared in this study showed interesting gas permeation results, and we consider that the ion irradiation would be one of the important membrane fabrication techniques for realizing a high gas permeability and selectivity.