OSCILLATORY SHEAR ALIGNMENT OF A LIQUID-CRYSTALLINE POLYMER

The alignment of a semiflexible main-chain liquid crystalline polymer by oscillatory and steady shear is investigated in the nematic and sme ctic states by rheometry and X-ray scattering. Steady shear of the nem atic produces alignment in the now direction, whereas dynamic shear pr oduces planar alignment parallel to the now and neutral directions. In the smectic state, alignment of the layer normal along the neutral di rection was predominant - the result of various frequencies and strain amplitudes. The predominance of this alignment arises from the high d egree of interlayer connectivity characteristic of main-chain liquid c rystals. More surprisingly, for certain alignment procedures (those wi th strain amplitude less than 5% and moderate to low frequency), align ment of the layer normal is approximately parallel to the now directio n. Alignment parallel to the velocity-gradient direction was found onl y when another smectic form, having less interlayer connectivity, was induced by the deformation process. This study demonstrates a rich rel ationship between applied shear now, phase behavior, and the molecular orientation.