The mechanism of polymer alignment of liquid-crystal materials

TLDR

Smetic and nematic liquid‑crystal materials can be homogeneously aligned by buffed thin films of appropriate polymers. We propose that the buffing process orients the polymer’s molecular chains in a manner similar to cold drawing of bulk polymer samples. Experimental verification of this theory is obtained by measuring buffing‑induced birefringence in thin films of various polymers coated on glass. Further experiments show that polymer chain orientation—not surface scratching—is required for alignment, that alignment occurs only when the polymer is both oriented and crystalline, and that a liquid‑crystal phase forms on the crystalline, oriented surface analogous to epitaxial growth of conventional solid crystals.

Abstract

Smetic and nematic liquid-crystal materials can be homogeneously aligned by buffed thin films of appropriate polymers. We propose that the buffing process orients the polymer’s molecular chains in a manner similar to cold drawing of bulk polymer samples. Experimental verification of this theory is obtained by measuring buffing-induced birefringence in thin films of various polymers coated on glass. Further experiments establish that the oriented state of the polymer chains, and not scratching or grooving of the surface, is necessary to produce alignment. Alignment is found to occur when the polymer is both oriented and crystalline. A picture of alignment is presented in which the formation of a liquid-crystal phase on the crystalline,oriented polymer surface is analogous to the epitaxial growth of conventional solid crystals.