Binary nematic mixtures components

Figure 25. Inverse of selective reflection maxima (o=p) as a function of composition for a number of binary chiral nematic mixtures. Here the components are O cholesteryl formate/cholesteryl chloride (at 50 °C), A cholesteryl propionate/cholesteryl chloride (at60°C), cholesteryl heptanoate/cholesteryl chloride (at 60 °C), A cholesteryl laurate/cholesteryl chloride (at 60°C) [105],...

In this paper, an earlier theory (12-13) for binary mixtures of backbone LCPs (and/or nonpolymeric molecules) in the nematic (N) LC phase and the isotropic (I) liquid phase has been extended to treat binary mixtures in multiple smectic-A (SA) LC phases, the N LC phase, and the I liquid phase. Either component 1 (Cl) and/or component 2 (C2) in the mixture can be a backbone LCP, a nonpolymeric LC molecule, a polymeric non-LC molecule, or a nonpolymeric non-LC molecule. Cl can also be a side-chain LCP or a combined LCP (including a SS LCP). The new theory of this paper is the mixture analogue of an earlier theory for pure (single-component) systems derived and presented in detail in References 3 and 7-10 (see also References 14-23). When only one component is present, the new mixture theory of this paper reduces to this earlier single-component theory. Therefore, only a short summary of the new mixture theory is presented here. 

Fig. 3. Calculated and observed nematic-isotropic phase diagrams for binary mixtures of homologous 4,4 -di-n-alkyloxyazoxybenzenes. Solid line is calculated by regular solution approximation. A denotes point calculated assuming ideal solution. denotes experimentally observed point. 3-6 means 4,4 -di-n-propyloxy in mixture with 4,4 -di-n-hexyloxyazoxybenzene. X is mole fraction of ith component.

Illian et al. [82] studied the pressure effect on the phase transition behavior of binary mixtures of terminally polar and nonpolar components which exhibit induced SmA phases. The re-entrant N phase is stabilized by increasing pressure and at about 101 MPa the SmA-re-entrant N phase boundary meets the N-SmA one. At higher pressures a nematic gap appears and finally the SmA phase on the polar side of the temperature-mole fraction diagram (175 MPa) disappears. 

Diffusivities of binary, ternary and multi-component liquid crystalline mixtures, e.g. of soap (potassium laurate (PL), water [25, 58], and lipid (dipalmitoylphosphatidylcho-line (DPPC) [25, 59] systems in lamellar, hexagonal, cubic, nematic and micellar mesophases [25,60,61] have been studied extensively by pulsed-field-gradient NMR [25] and optical techniques [62], partly because of their intimate relation to the structure and dynamical performance of biological membranes [18]. The main distinction from thermotropic phases is that for layered structures a noticeable diffusion occurs only within the layers (i.e. lateral, frequently written as Dl, but in our notation DjJ, whereas it is negligibly small and difficult to detect across the layers [60-62] (transverse migration, for bilayers denoted by flip-flop ) so the mobility is essentially two dimensional, and the anisotropy ratio is so great that it is seldom specified explicit-... 

An advantage of NMR in the investigation of phase transitions is the fact that bi-phasic regions can be detected from the superposition of two different components in the spectrum. This facilitates the distinction between discontinuous (first-order) and continuous (higher-order) transitions (see Sec. 1.3.5). The tricritical point of the smectic A to nematic phase transition for binary liquid crystal mixtures, for example, has been determined by 2D NMR [54]. 

The study of binary mixtures of LMMLCs has attracted considerable attention since the earliest days of LC research. Mixtures have played an important role in the technology of LC display devices by extending the range of the nematic phase to room temperature. Moreover, extrapolation of the transition temperatures of binary systems involving a non-mesogen sometimes provides an estimate of the virtual transition temperature of the latter component. This is a quantity of theoretical interest and one which obviously cannot be determined experimentally from study of the non-mesogen as a single component. 

The orientation technique of colloid suspensions in a nematic host has been successfully applied to the analysis of pharmaceutical products, especially for analysis of polymorphs or solid multicomponent mixtures (up to five components) [33]. In some of the described compounds, the method appears to be unique for experimental infrared (IR) band assignment. On this basis, quantitative approaches for the determination of pharmaceutical products in solid binary mixtures have been presented. An interesting practical field of application has been established in the analysis of the polymorphs of pharmaceutical products. We will now demonstrate the applicability of the method for the elucidation of some of the best-selling drugs (depicted in Figures 5.1 through 5.3). 

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