Nematic unstable region

Figure 1 shows the phase diagram for a = 3.4, n, = 1.5, and Up = 40. The temperature is normalized by the NIT temperature of the pure liquid crystal. The solid (broken) lines correspond to the binodal (spinodal) lines. The dashed-and-dotted line shows the NIT line. In the region between the binodal and spinodal lines, there are two metastable regions an isotropic metastable (Im) and a nematic metastable (Nm). In the low temperature of the spinodal line, we have an isotropic unstable (lu) and a nematic unstable (Nu) regions. At lower temperatures, the biphasic region where a nematic and an isotropic phase coexist appears. The stable nematic phase appears in a dilute region of the polymer concentration. The nematic and isotropic binodal lines intersect at 0 = 0 and T = T. ... 

In a uniaxial nematic, the particle-like soliton amounts to a director configuration distorted in a region of finite size, outside of which the director field is uniform. As a rule, such solitons are unstable with respect to a decrease in size and subsequent disappearance on scales smaller than the... 

In this section, we focus on the interplay between phase separations and phase ordering kinetics in mixtures of a flexible polymer and a liquid crystal (nematogen). When the system is thermally quenched from a stable isotropic phase into an unstable part of the biphasic region, the fluctuations of concentration and orientation take place and isotropic or nematic droplets appear with time [109, llOj. The instability of these systems is driven by the competition between phase separation and nematic ordering. Figure 2.22 shows the phase diagram of the polymer/liquid crystal mixture with Up = fir = 2 and a = 1.4. The solid curve refers to the binodal and the dotted line shows the first-order NIT. The dash-dotted line shows the spinodal. The arrows indicate temperature quenches from a stable isotropic phase... 

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