Characterization of Alignment Correlation between LC Molecules and Chemical Groups on/in the Surface of Polyimide Films with Biphenyl Side Chains

In this study, the surface chemical structure and molecular conformation of one kind of PI alignment film achieving vertical alignment were investigated by XPS, ATR-FTIR, and polarized ATR-FTIR, and the LC alignment on PI film was studied by transmission polarized FTIR It was found that some chemical groups, such as biphenyl and imide ring, oriented perpendicular to the plane of alignment film while the molecular backbones took the conformation parallel to the plane of film. At the same time, the biphenyl groups of LC molecules in LC cell were aligned perpendicular to the alignment film. Thus, the alignment consistency between the biphenyl in the surface and LC molecules was proved first, which powerfully indicated that the chemical groups in the surface taking a vertical conformation on the surface play an essential role in producing a vertical LC alignment and the conformation of groups in the surface determines the size of pretilt angle.