ラビングによるポリイミド薄膜の化学構造, 帯電性, 光電子放射特性の変化

概要

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Mechanical rubbing of polyimide (PI) films is used to homogeneously align liquid crystal molecules on the surface. The chemical structure of aromatic PI surfaces subjected to rubbing has been analyzed by X-ray photoelectron spectroscopy, and the frictional charging and surface states of the PI films have also been investigated by measurements of surface potential (SP) and photoelectric emission (PE). Six kinds of PI films were prepared by reacting two diamines containing CH3 and CF3 functional groups with three tetracarboxylic dianhydrides. Rubbing of the films caused the O content to increase, while the N and F contents decreased. The fraction of the two oxygen components (-O- and C=O) of the films was changed by the rubbing. The films with CF3 groups exhibited much more negative charging (negative SP) than those with CH3 groups. It is suggested that the order of the charging of the films with CF3 and CH3 groups closely depends on the ratio by which the F and N elements, respectively, were reduced by the rubbing. Both with and without rubbing, the films with CH2 groups gave a considerably larger PE level than those with CF3 groups. This suggests that the electron trap levels responsible for the negative charging in the latter films make virtually no contribution to PE.
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