Light Diffraction Studies of the Banded Texture in Hydroxypropyl Cellulose

In most liquid crystal polymers when a thin sample is sheared the polymer exhibits a periodic pattern or texture. While this phenomena has been widely noted, a complete and satisfactory explanation is not yet in hand. We present the results of a study of the dynamics of the formation of the banded texture in liquid crystalline polymers after shear. The data were collected by the diffraction of light from the texture. This approach directly provides the key parameters to characterize the texture without the ambiguity that is often involved with microscopy. It was found that the overall nature of the modulation that gives rise to the texture appears to not vary with time except in magnitude. Both thewavelength and the coherence length of the modulation remain fixed. While both shear rate and thickness of the sample have little effect upon the texture, concentration of the polymer has a very large effect.