We have investigated the pretilt angle of liquid crystal ͑LC͒ molecules induced by photoaligned films of a series of polyimides. The polyimides were random copolymers synthesized from pyromellitic dianhydride and a mixture of 4 , 4Ј-diaminoazobenzene and 4-͓4Ј-propylbi͑cyclohexan͒-4-yl͔phenyl 3,5-diaminobenzoate ͑PBCP-DABA͒. PBCP-DABA is a diamine to introduce a side-chain structure into polyimide. We found that the pretilt angle of LC molecules can be controlled from 0°to 90°by varying the molar fraction ͑x͒ of PBCP-DABA from 0 to 0.5. Defect-free uniform LC alignment was observed for x Յ 0.125 and x Ն 0.3, but threadlike textures appeared for 0.15Յ x Յ 0.25. Since the interaction between the polyimide backbone structure and the LC molecule may be blocked by relatively dense side-chains, the appearance of threadlike texture is tentatively attributed to weak azimuthal anchoring strength of the photoaligned polyimide films with x Ն 0.15.

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