Flow-induced Textures and their Relaxation Behavior

6 Flow-induced Textures and their Relaxation Behavior 

The evolution from the static state to different textures observed as a consequence of controlled shearing experiments and the subsequent relaxation behavior at the cessation of flow were first analyzed by Grazia-no and Mackley [96] for a number of thermotropic MCLCPs. This pioneering work introduced and defined the terms used today to classify shear-induced textures worm texture, ordered texture and banded texture. It should be noted that these textures have also been observed in lyotropic nematics. 

The shearing behavior of MCLCPs depends on the initial state of the material. When molten MCLCPs exhibiting a threaded texture in the quiescent state are subjected to shear, the threads first extend and curve and disclination loops distort within the shear. However, at a rather well defined shear strain multiplication of the defects occurs [83, 84, 96, 97]. These defects appear as short, dark curled entities which flow along the streamlines whilst continually changing their shapes, and the overall view of them during shear resembles a vat of 

Concerning the mathematical modeling of LCPs, most attempts have concentrated on lyotropic systems. Doi [103] has developed a defect free model for lyotropic rodlike polymers in the isotropic and anisotropic states and Larson and Mead [ 104] have proposed a polydomain phenomenological description of lyotropic systems. Marrucci and Maffettone [105] solved a diffusion 

119-123], which has been predicted theoretically [124, 125]. A finite time must elapse from the onset of shear [109] or the cessation of shear [120, 122] before the bands can form. 

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The self-organizing nature of liquid crystal polymers is reflected in their complex flow behavior. The relaxation phenomenon of lyotropic polymer solution after shear cessation leads to band texture morphology that can be further induced to isotropic materials. Future research should focus on solvents influence on band size implicitly related to the induced pattern in polymers with different structures. Another aspect that could be explored is the imidization of patterned polyimide precursors and those conditions in which the texture is still maintained. 

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