Solidification-induced and shear-induced band texture in thermotropic liquid crystalline polymer films

Abstract

It has been observed that the band texture of thermotropic liquid crystalline polymers (LCPs) is formed at the shearing temperature during the relaxation of shear. The band spacing increases with increasing shearing temperature between T _m and T _i, but is independent of shearing rate within the range of our experiments. The angle of zigzag orientation of the molecular chain fibrils with respect to the direction of shear is independent of the shearing temperature. The relaxation rate of the shear-induced band texture depends on the width of the bands formed. The wider the band spacing is, the slower the relaxation. When specimens with shear-induced bands of different spacings are annealed at a certain temperature for 10 min, they are all converted to a new band texture of the same spacing of around 1 μm. These bands with a small spacing generated during cooling are termed the solidification-induced band texture. When the specimen with shear-induced bands is annealed for a short time, so that the bands have not relaxed, and is then quenched, solidification-induced bands with a smaller spacing than the original bands appear. In this way, both shear-induced and solidification-induced bands could be seen in the same polarizing micrograph. The solidification-induced bands could be used as a kind of decoration to show that the chain orientation field follows the changes during relaxation of a shear-induced texture, at a given temperature, into walls, loops and sinusoidal wave textures which eventually relax to a thread texture.