Study of local stress, morphology, and liquid-crystal alignment on buffed polyimide surfaces

Hirotsugu Kikuchi, J. A. Logan, Do Y. Yoon

Research output: Contribution to journalArticle

73 Citations (Scopus)

Abstract

The magnitude of local stress applied to a polymer surface in the buffing process, which is a critical method to uniformly align liquid crystals for displays, has been evaluated from the polarizing optical microscopic investigation of nematic liquid crystals in contact with polyimide surfaces which were suitably buffed in order to visualize the individual tracks of the buffing rayon fibers. The estimated magnitude of local stress is most likely to be far greater than the yield stress of the polymer film, thereby causing permanent molecular orientation along the buffing direction. The surfaces of poly(amic acid) and cured polyimide films, subjected to different buffing and cure profiles, have been examined by atomic force microscopy. The ability of these buffed polymer surfaces to align nematic and chiral smectic C (ferroelectric) liquid crystals were also investigated. These studies show that the presence of microgrooves on buffed polymer surfaces is not necessary for alignment of liquid crystals. The contribution of polymer molecules from the buffing fibers, deposited and oriented on the polyimide surfaces during buffing, can also be ruled out. Rather, it is concluded that the liquid-crystal alignment is mainly caused by the anisotropic interactions between liquid-crystal molecules and the polymer segments oriented through plastic deformation, with little contribution from frictional heating. For the alignment of smectics, both the degree of order and mechanical properties of polyimide films are found to be important factors.

Original languageEnglish
Pages (from-to)6811-6817
Number of pages7
JournalJournal of Applied Physics
Volume79
Issue number9
DOIs
Publication statusPublished - May 1 1996

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polyimides
liquid crystals
alignment
polymers
rayon
fibers
plastic deformation
molecules
atomic force microscopy
mechanical properties
acids
heating
profiles
interactions

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Cite this

Study of local stress, morphology, and liquid-crystal alignment on buffed polyimide surfaces. / Kikuchi, Hirotsugu; Logan, J. A.; Yoon, Do Y.

In: Journal of Applied Physics, Vol. 79, No. 9, 01.05.1996, p. 6811-6817.

Research output: Contribution to journalArticle

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