Control of LC Alignment by Polyimide Film Exposed to Pulsed Laser of Long Wavelength (355 nm)

Abstract

The alignment of nematic liquid crystals (LCs) parallel to the polarization direction of laser could be induced by PI(PBGA/FDA) with a fluorene unit exposed to the laser at 355 nm in nitrogen atmosphere. The structure of PI(PBGA/FDA) irradiated with the laser in nitrogen shows no detectable chemical change, when the parallel alignment of LC is induced. The mechanism of the parallel alignment is not the photodegradation but the orientation of main chains of the polymer. It is estimated that the reason that LC alignment is dominated not by main chain but by fluorene unit is the multiplier effect of alignment force from two coplanar phenyl ring in the fluorene unit.