Liquid crystalline polymers domain texture

These different contrast mechanisms can all be used to reveal the scale of liquid crystalline polymer microstructures. In specimens that exhibit a mosaic texture, and in those that contain predominantly planar defects, domain size is easily defined in terms of areas that uniformly show extinction between crossed polars. However, if the defects are predominantly linear, as in specimens that exhibit schlieren textures, such simple characterization of microstructural scale is no longer possible. Here it is more convenient to look at the length of disclination line per unit volume, which is equivalent to the number of lines intersecting unit area, and analogous to the dislocation density as defined for crystalline solids. Good contrast is essential in order to obtain an accurate count. Technologically, microstructural scale is of growing interest because of its relevance to processability, mechanical properties and optical transparency. 

Larson, R.G. Doi, M. Mesoscopic domain theory for textured liquid-crystalline polymers. J. Rheol. 1991, 35 (4), 539-563. 

Larson, R. G., and Doi, M., Mesoscopic domain theory for textures liquid-crystalline polymers,... 

A TEM thin section of an unstained LCP with 5% polycarbonate is shown as an example in Fig. 5.100, as prepared by Wood [273]. Ultramicrotomy of the blend shows the typical banded texture of the LCP with the dark submicrometer isotropic polycarbonate domains uniformly dispersed in the ordered matrix. It is worth noting that although there is extensive research going on in university laboratories today there are few major commercial products which are blends with LCPs. In most cases this is due to the mismatch in thermal and rheological properties which results in materials which have physical properties that resemble the thermoplastics rather than the liquid crystalline polymers. 

More recently, polymers 124b-f have been reported that contain liquid crystalline (LC) substituents [170]. Unlike 124a, these polymers were soluble in CHCI3 and THF and GPC characterization gave M of 5400-8100, with fairly narrow PDIs (1.2-1.4). While the polymers showed polymorphic texture, the texture exhibited was not satisfactory for a typical LC phase, potentially due to randomly oriented domains. All the pristine polymers were dark blue and Eg values of 1.2-1.3 eV were determined from the absorption onset. Iodine-doped films gave conductivities of 5.2 x 10 -3.2 x 10 S cm . All properties seemed fairly independent of the LC side chain used. 

The formation of banded textures in thin-film samples of solutions of hquid crystalline polymers (LCPs), subjected to shear, has been reported in the literature since 1979 [15]. Because of the symmetrical properties of the liquid crystal solutions, large domains of weU-oriented polymer chains are formed during shear flow, while defects are squeezed into small regions. The shear accounts for an additional energy stored in the solution. When the shear is stopped, the system will first relax with a characteristic time fb to a transient state. In this state the distortion energy is minimized, and the orientational order is kept, resulting in a banded stmcture. This behavior is observed only if two conditions are fulfilled [16] ... 

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