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

本研究采用高真空仪器和Baratron绝对压力计，在76cmHg和35°C条件下，测量了离子辐照下不对称聚酰亚胺膜的气体透性和选择性。采用干湿相转化法制备了不对称聚酰亚胺膜，并在50keV下用lx1012 ~ 3x1015（He+/cm2）离子照射膜的表面表皮层。我们证明了He+辐照膜的气体选择性随着离子影响的增加而增加，并且辐照离子在皮肤层的能量损失深度分布对不对称膜的气体渗透性和选择性有显著影响。在低离子影响下，膜的气体渗透率增加，在高离子影响下，膜的气体渗透率降低。另一方面，气体选择性随离子影响的增加而增加。一种可能是在离子照射的皮肤表面形成了气体渗透空间，使得气体分子之间的大小和形状具有高度的区别，抑制了N_2和CH_4的渗透性，而不是O_2和CO_2的渗透性。另一个有趣的结论是，离子辐照皮肤层的厚度对气体渗透性和选择性有显著影响。离子辐照后表层聚酰亚胺的结构与离子能量损失的多少密切相关，从而决定了膜内形成的自由体积和自由体积分布。希望制备一种既具有高透气性又具有气体分离选择性的聚合物膜。本研究制备的离子辐照不对称聚酰亚胺膜具有有趣的透气性，我们认为离子辐照将是实现高透气性和选择性的重要膜制造技术之一。

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.