Polymeric samples, mechanical deformation

As it was mentioned above mechanical properties of polymers are strongly dependent on the temperature. Therefore, E and D, for a polymeric sample are dependent on the temperature at which the experiment is performed. On the other hand the mechanical properties of polymers are also dependent on time. Therefore E and D are not constant at one temperature but evolve with time i.e. E(t), D(t) [7], The complex relationship between the configurational distorsion produced by a perturbation field in polymers and the Brownian motion that relaxes that distorsion make it difficult to establish stress-strain relationships. In fact, the stress at that point in the system depends not only on the actual deformation but also on the previous history of the deformation of the material. 

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. 

Disordered samples of polydiacetylenes can be prepared by a number of routes. First, the less perfectly polymerizing crystals can be obtained in a fibrilar form due to disruption of the crystal lattice by internal strain, e,g, (120). Secondly, similar samples can be obtained by the removel of unreacted monomer from partially polymerized crystals. Thirdly, single crystals can be deformed mechanically. Fourthly precipitates in the form of films or powders can be obtained for soluble diacetylenes and finally the solutions of such soluble materials can be studied directly. 

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