Rubbing-Induced Side Chain Alignment at the Surface of N-Substituted Aromatic Polyamide Film as Studied by Charge-Transfer Absorption Dichroism

Spin-coated N-anthrylmethyl poly(p-phenylene terephthalamide) (AM-PT) film, which showed good liquid crystal alignment after rubbing, was prepared on a quartz plate, and rubbing-induced side-chain alignment was studied by means of charge-transfer (CT) band dichroism. By immersing the samples in methanolic 2,4,5,7-tetranitro-9-fluorenone (TENF) solution, a CT complex between the anthrylmethyl side-chain and TENF was formed only at or near the surface. The rubbed film showed smaller CT absorption compared to film without rubbing. The CT absorbance of the rubbed film to the linearly polarized light parallel to the direction of rubbing was significantly larger than that the perpendicularly polarized light, giving a dichroic ratio of (1.34 ± 0.14 (S.D.), n = 3), though films without rubbing showed no dichroism (1.02 ± 0.01 (S.D.), n = 3). The results confirmed the rubbing-induced orientation of the anthrylmethyl side-chain, demonstrating that this method offers the direct and sensitive way to monitor rubbing-induced conformational change of the polymer at the surface.