Annihilation, textures

If (1), (2) or (3) prevail, the morphology is metastable and will evolve upon isothermal mesophase aging. Case (1) and case (2) will be mentioned in subsequent sections. Case (3) represents the well known texture defects within PLC mesophases. The N phase in PLCs tends to be formed by coalescence of a large number of very small droplets and is initially characterized by a high density of disclination defects (around which the director orientation varies). These are progressively annihilated upon isothermal annealing [53] and visualized in the coarsening of the N texture observed by microscopy or SALS. 

Figure 2.22 exhibits the generation of LC phase and time evolution of LC texture for 60120120 (mole ratio) ANA/AAA/IA at the reaction temperature of 320°C. For this system, the LC phase appears simultaneously with a high density of defects. And then, the annihilation between defects occurs rapidly to release the excess free energy. The circles in Figure 2.22 illustrate a typical example of the annihilation process when reaction time is between 48.0 s and 50.0 s, for which the annihilation rate is about 23 p.m/s. In the 60/20/20 ANA/AAA/IA reaction system, it only takes a few seconds to accomplish the annihilation process. 

Another example is formation of boodjooms at the cell surfaces. Now we are interested not in the linear disclinations responsible for the SchUeren texture but in their nuclei at the solid substrates limiting a liquid crystal cell. The linear discUna-tions of strength s = 1 may annihilate within the bulk due to some reconstruction of the director field induced, for instance, by temperature or a flow of the material. For example, a bulk discUnation of strength s = +1 shown by the solid vertical line in Fig. 8.18b disappears but its nuclei localized at the surfaces transform into new, surface defects. Fig. 8.18c illustrates the situation at one of the two surfaces. The escaped line leaves behind it a boodjoom. We meet such a situation in thick planar cells where the Schlieren textures with four brushes are observed. 

Beta solution heat treatment followed by subsequent martensitic transformation tends to annihilate prior texture. For example, Transage 175 sheet that was unidirectionally cold rolled for the final 47% reduction and heat treated at 760 C (1400 °F), 1/2 h, fan air cooled, 480 °C (900 °F), 48 h, AC had tensile properties as follows ... 

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