Polyimides with Fluorinated Side Chains for Liquid Crystal Alignment

Abstract

The surface properties of a series of polyimides with fluorinated alkyl side chains are studied by contact angle and pretilt angle measurements. The contact angles depend on the fluorine content of the polyimides. Higher pretilt angles are obtained for polyimides with longer fluorinated side chains. The pretilt angles, however, not only depend on the side chain length, but also on the main chain structure of the polyimides. Polyimides prepared from benzophenone tetracarboxylic dianhydride are found to show higher pretilt angles than those prepared from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride. The anisotropic interaction between polyimide molecules and liquid crystal molecules is discussed.

Key Words:

• liquid crystal
• pretilt
• polyimide
• fluorinated polyimide
• surface tension