Oscillatory Shear Alignment of a Liquid Crystalline Polymer

ALT, D. J.; HUDSON, S. D.; GARAY, R. O.; FUJISHIRO; K.

MACROMOLECULES

AMER CHEMICAL SOC

Lugar: Washington; Año: 1995 vol. 28 p. 1575 - 1579

0024-9297

The alignment of a semiflexible main-chain liquid crystalline polymer by oscillatory andsteady shear is investigated in the nematic and smectic states by rheometry and X-ray scattering. Steady shear of the nematic produces alignment in the flow direction, whereas dynamic shear produces planar alignment parallel to the flow and neutral directions. In the smectic state, alignment of the layer normal along the neutral direction was predominant-the result of various frequencies and strain amplitudes. The predominance of this alignment arises from the high degree of interlayer connectivity characteristic of main-chain liquid crystals. More surprisingly, for certain alignment procedures (those with strain amplitude less than 5% and moderate to low frequency), alignment of the layer normal is  approximately parallel to the flow direction. Alignment parallel to the velocity-gradient direction was found only when another smectic form, having less interlayer connectivity, was induced by the deformation process. This study demonstrates a rich relationship between applied shear flow, phase behavior, and the molecular Orientation.