The effects of fluorination on the vacuum surface flashover voltage of polyimide

The effects of fluorination on the vacuum surface flashover voltage (U
f
) of polyimide (PI) are researched. The experimental results show that as the degree of fluorination increases, the U
f
of PI firstly increases and then decreases, the highest U
f
in the experiments is increased by up to 21 % compared with untreated PI sample. The results of Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectric spectroscopy (XPS) show that fluoride treatments may cause the structural change of PI. A mechanism based on the abstraction of the atoms of H, O and N is proposed. During the process of fluorination, the formation of the C-F bonds can improve the surface flashover voltage, whereas as the degree of fluorination increases, the destruction of the C-N bonds would degrade the surface flashover performance. The two processes play the role at the same time. Therefore, there is an optimal degree for the fluorination.