Effect of Flexible Chain Length on the Photoorientation Behavior of Surface-Grafted Liquid Crystalline Azobenzene Block Copolymer Brush

Abstract

A liquid crystalline (LC) azobenzene homopolymer brush film of poly[4-(10-methacryloxydecyloxy)-4′-pentylazobenzene] (P5Az10MA), and two diblock copolymer brushes consisting of the same LC azobenzene (Az) block connected with poly(hexyl methacrylate) block (PHMA-b-P5Az10MA) have been synthesized on initiator-immobilized quartz surfaces by atom transfer radical polymerization. In the diblock polymer brushes, the length of PHMA blocks tethering to the substrate surface were changed (26 nm and 51 nm). The orientation and structural features of the liquid crystalline block, containing an Az mesogenic group of the polymer brushes were evaluated by UV-vis spectroscopy and grazing incident X-ray diffraction measurements. Upon irradiation with 436 nm linearly polarized light (LPL), the levels of photoinduced in-plane anisotropy and reorienting behavior among the brushes showed significant differences as a result of degree of freedom of the flexible buffer chain spacers.

Keywords:

• Azobenzene
• block copolymers
• diblock copolymer polymer brush
• flexible spacer chain
• grafted thin film
• liquid crystalline polymer
• optical anisotropy
• photoorientation
• surface-grafting
• surface-initiated polymerization

Acknowledgments

The authors thank Mr. T. Hikage, Dr. M. Hara, Mr. S. Kakehi and Mr. A. Nishimi for their support in conducting high intensity X-ray analysis. The research was supported by the Grant-In-Aid for Basic Research S (No. 23225003 to TS) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and PRESTO program (To SN) of Japan Science and Technology Agency.