Mesogens orientation

Quite early on, structural investigations showed [17] that the mesogens in the main chain and the side chain orient parallel to one another. This was confirmed by electron microscopy [18], X-ray diffraction [6,7,13, 14, 17, 19, 20] and HNMR spectroscopy [21]. Following the general classification of LC side-chain polymers (Figure 2) [22], these polymers should be classified as type III. In these combined LC polymers, the polymer chains and mesogens orient parallel to one another to define the LC director. 

Fig. 10.4 Scheme of the jaeparation process of a CLCP nanocomposite film with mesogens oriented parallel to CNTs and b CLCP nanocomposite film with mesogens oriented perpendicularly to CNTs and their distinctive photomechanical behaviors. Reproduced with permission... 

The application of the previously discussed techniques to induce monodomain structures in side-chain liquid-crystalline polymers by the application of electric or electromagnetic fields, by shearing or on anisotropic surfaces, frequently leads to comparatively low, macroscopically uniform orientation. Additionally, the methods are limited to a sample thickness of about 100 pm. Liquid-crystalline side-chain elastomers do not have this restriction, because a high macroscopic orientation can be induced in polymeric networks by mechanical deformation up to a sample thickness of about a centimeter [103, 109]. The synthesis of such systems can be performed by crosslinking linear, side-chain liquid-crystalline polymers to networks [llOj. The inherent combination of rubber elasticity and liquid-crystalline phase behavior, may then be exploited for the induction of a macroscopic mesogen orientation by mechanical deformation. 

During interval I the stress increases linearly with strain and no significant changes in the mesogen orientation can be observed. 

Figure 2-52. Possible mesogen orientations during the reorientation process at S=0 Oi-direction of internal stress induced during the second crosslinking step, Oci direction of external stress applied during the rheo-optical experiment), (a) Homeotropic orientation perpendicular to the film plane (b) isotropic orientation (c) planar biaxial orientation.

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