Nematic-isotropic transition temperature scaled

Figure 26. The dependence of the nematic-isotropic transition temperature, scaled with that for the...

At the nematic-isotropic transition temperature T i, also called the clearing point, 1(7, ) is determined by eqn (6.6). Thus, by measuring T i as a function of the concentration c, the scaling constant q can be determined from the relation... 

Figure 20. (a) Orientational correlation time t in the logarithmic scale as function of the inverse of the scaled temperature, with the scaling being done by the isotropic to nematic transition temperature with Ti-N. For the insets, the horizontal and the vertical axis labels read the same as that of the main frame and are thus omitted for clarity. Along each isochor, the solid line is the Arrhenius fit to the subset of the high-temperature data and the dotted line corresponds to the fit to the data near the isotropic-nematic phase boundary with the VFT form, (b) Fragility index m as a function of density for different aspect ratios of model calamitic systems. The systems considered are GB(3, 5, 2, 1), GB(3.4, 5, 2, 1), and GB(3.8, 5, 2, 1). In each case, N = 500. (Reproduced from Ref. 136.)... 

Fig. 3.10. Magnitude of the flexoelectric coefficient e3 versus the temperature deviation from the nematic-isotropic phase transition for (a) ClPbislOBB and for (b) 5CB. Data taken from Harden et al Note the three orders of magnitude difference in the vertical scales ...

For compounds in the nematic state, the order parameter is strongly affected by the temperature. The experimental behavior is related with a theoretical prediction derived in using a simple inner field theory (12). A reduced temperature scale is used in fig.2 defined by Tj. = KKIT/T, where is the nematic to isotropic transition... 

Thickness profiles of microdroplets of the very common 5CB liquid crystal on bare, oxidized silicon wafers appear on Fig. 5.6. The nematic-isotropic (Nl) transition temperature Tni is close to 35°C. The scenario is complex, both at the molecular and at mesoscopic scale. 

The values of the scaled transition temperature, l TNi/e2oo, together with the transitional values of the ord parameters ni, ni and ni are listed in TABLE 1 for several values of the biaxiality parameter, X. As the molecular biaxiality increases so the major order parameter at the transition decreases indeed when X is 0.3 ni has decreased to about half that for a uniaxial molecule. In contrast although as expected the biaxial ordo- parameter ni increases with X the value is extremely small. It would seem, therefore, that the molecular biaxiality has the greatest effect on Ni and that ni is essentially negligible. The influence of X on the second rank order parameter is mimicked by its fourth rank counterpart ni indeed when X is 0.3 this order parameter is four times smaller than that for uniaxial molecules. For X of 0.4 all of the transitional order parameters are extremely small, hinting at the approach of a second ord transition. This occurs when X is 1 / >/6 but now the transition from the isotropic phase is directly to a biaxial and not a uniaxial nematic phase, as we shall see. 

Notice, that d = 1 corresponds to the equilibrium phase coexistence temperature. The values d = 9/8 and = 0 are the upper and lower limits of the metastable nematic and isotropic states, respectively. The quantity <5k = 1 — T /Tk which sets a scale for the relative difference of the temperature from the equilibrium phase transition is known from experiments to be of the order 0.1 to 0.001. On the other hand, it is related to the coefficients occurring in the potential function according to... 

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