Shear-induced band texture of side group liquid crystalline polymers

The shear-induced band texture of conventional end-on fixed side group liqu id crystalline polymers (LCPs) has been investigated by using polarizing op tical microscopy (POM), small angle light scattering (SALS) and infra-red d ichroism techniques. The band spacing is about 1 mum. which increases very slightly on increasing the temperature of shearing and is independent of sh earing rate within the range studied. The band texture is not seen to exhib it an interchange of dark and bright bands on rotation of the sample with r espect to the polarizer/analyser. but a typical periodical structure is ref lected by the SALS patterns of the band texture. The relaxation behaviour o f the bands indicates that the band texture formed here is the result of th e orderly aligning of domains exhibiting the focal-conic texture, and this is totally different from the case of main chain LCPs where the band textur e is substantially an optical effect of the periodic zigzag or sinusoidal s tructure of parallel aligned microfibrils. Infra-red dichroism and rotating parallel-plate shearing measurements show that the axes of the backbone of the polymer tend to orient in the shearing direction and the end-on fixed mesogenic side groups tend to align perpendicular to the shearing direction .