Binary nematic mixtures

Short-time Brownian motion was simulated and compared with experiments [108]. The structural evolution and dynamics [109] and the translational and bond-orientational order [110] were simulated with Brownian dynamics (BD) for dense binary colloidal mixtures. The short-time dynamics was investigated through the velocity autocorrelation function [111] and an algebraic decay of velocity fluctuation in a confined liquid was found [112]. Dissipative particle dynamics [113] is an attempt to bridge the gap between atomistic and mesoscopic simulation. Colloidal adsorption was simulated with BD [114]. The hydrodynamic forces, usually friction forces, are found to be able to enhance the self-diffusion of colloidal particles [115]. A novel MC approach to the dynamics of fluids was proposed in Ref. 116. Spinodal decomposition [117] in binary fluids was simulated. BD simulations for hard spherocylinders in the isotropic [118] and in the nematic phase [119] were done. A two-site Yukawa system [120] was studied with... 

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],...

Miscibility studies of the nematic dye-containing copolymers with suitable low molecular weight liquid crystals yield homogeneous nematic mixtures. A binary mixture of 4-cyanophenyl-4-heptylbenzoate and 4-cyanophenyl-4-pentylbenzoate is miscible with the phenylbenzoate-anthraquinone copolymers. 

Fig. 6. Phase diagram for the binary mixture of terminally polar mesogens showii the reentrant nematic (N), monolayer (Ai), partially bilayer (Ad) and two-dimensional (C) phases (Lobko et al. [47])...

Fig. 17 Phase diagram of a binary mixture of bent- (P8-0-PIMB) and rod-shaped (5CB) molecules. Cartoon showing the phase structures are also shown. In the B4/Iso and B4/N phases, 5CB molecules are in the isotropic and nematic phases [9]...

Kundu B, PratibhaR, MadhusudanaNV (2007) Anomalous temperature dependence of elastic constants in the nematic phase of binary mixtures made of rodlike and bent-core molecules. Phys Rev Lett 99 247802-1-4... 

A binary mixture of 4-pentylphenyl 4-pentylbicyclo[2.2.2]octane and 4-heptyl-phenyl 4-pentylbicyclo[2.2.2]octane, see Table 3.8, exhibits a wide nematic phase at room temperature with a high clearing point, a low birefringence (0.08), a moderate viscosity (46 cP) and a weakly negative dielectric anisotropy (Ae —1.1) measured at 20°C. It is a surprisingly good solvent for... 

Finkelmann and Stegemeyer have analyzed the composition dependence of the twisting power in binary mixtures of thermotropic liquid crystals, using the Goossens theory. The twisting angle

nematic layers is given as follows for a mixture of molecules of type 1 and 2,... 

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. 

Figure 4.10 Typical phase diagram of a binary mixture of nematic liquid crystals. By use of eutectic blocks of structurally similar compounds (e.g. alkyl homologs), the nematic phase range is extended to lower temperatures [32].

This can be also illustrated as follows a fatty man can be surrounded by 4 - 5 closely-packed fat men. But the same man can be surrounded even by 10 slim men. The latter can parallel the increasing dimensionality of space for the fat man. Consequently, the elongation of fluctuations due to the action of the strong electric field in the homogeneous phase of binary mixtures of limited miscibility is equivalent to increased dimensionality d = A. The uniaxial symmetry is natural also for the isotropic phase nematic liquid crystals. It may be considered for supercooled nitrobenzene due to intermolecular interactions (Fig. 5). ... 

By deuterium NMR, we have ascertained that the limit of solubility of 8a in the crystal-B phase is in fact somewhat less than 1.0 mol%. Under the conditions of our flash photolysis experiments, 8a is distributed between both a ketone-rich nematic phase and a ketone-depleted smectic phase at temperatures between 53-35°C. At 35°, the ketone-rich phase is transformed into a "p-phase" in which the ketone exhibits isotropic H and C NMR behavior, and which eventually crystallizes (though not under these conditions) to form a stable binary smectic or solid modification consisting of 8-10 mol% ketone and CCH-4. Thermal microscopy experiments with mixtures containing 1-3... 

In this section, we describe and explain some aspects of a thermally induced phase separation of a binary mixture containing a nematic liquid crystal forming the continuous phase. The first three subsections deal with a detailed description of the experimental observations. The phase diagram of the mixture, the scenario of the phase separation as well as the structures obtained after long times after the temperature quench are presented. The fourth subsection is devoted to a discussion of the experimental results on the basis of the concepts described in Sect. 2. In the fifth subsection, we report on the kinetic aspects of the phase separation. 

Fig. 2. Partial phase diagram of the binary mixture liquid crystal E7/silicone oil (Aldrich). is the E7 weight fraction. The Fig. shows an isotropic phase (1) above 60°C, a coexistence domain between an isotropic and a nematic phase (1+N) below 60°C, and a nematic phase (N) in the extreme right part of the diagram. The systems are quenched from the nematic domain to 20°C as indicated by the arrow...

Since the liquid crystal forms the continuous phase of the binary mixture, we are only interested in a small part of the total phase diagram. Weight fractions of the liquid crystal in the range 0.9 to 1 were used to determine the partial phase diagram of the mixture which is shown in Fig. 2. The system forms an isotropic (I) phase at high temperature, and a diphasic equilibrium between an isotropic and a nematic phase (N-i-I) at low temperature. A nematic domain (N) is found at intermediate temperatures and low silicone oil concentrations. As pointed out in the experimental section, the existence of this nematic domain has some importance prior to quenching the system to the diphasic region. The present mixture exhibits classical features usually observed in other mixtures of nematic liquid crystals and polymers or isotropic fluids [29,30]. 

Figure 19. Typical trajectories of the unit orientation vector for a single ellipsoid revolution in two different systems, (a) Calamitic system GB(3,5,2,1) at four temperatures (i) T = 2.008 (in the isotropic phase), (ii) T = 1.396 (close to the I-N transition), (iii) T = 1.310 (close to the I-N transition), and (ii) T = 1.192 (in the nematic phase), (b) Binary mixture at the highest temperature (left) and the lowest (right) temperature studied. (Reproduced from Ref. 131.)...

The resulting mixtures revealed the existence of columnar mesophases, with a pronounced intracolumnar order, the stacking periodicity being in the range from 3.40 to 3.45 A. The same type of ordered columnar mesophase has been induced by mixing discotic nematic compounds with TNF. In this case, the interactions between the disks are too small in themselves to favour a columnar mesophase, but the incorporation of electron acceptor molecules such as TNF contributes to enhance the intermolecular interactions and to generate an ordered columnar mesophase. The stabilization of the columnar structure in these binary systems has been found for other types of molecules... 

The dipalladium organyls 51, derived from 49 (M = Pd, X = C1) by ligand exchange reaction between the bridging group and acetylacetonate, are not mesomorphic in their pure state, but form mesomorphic charge transfer systems with the electron acceptor TNF [95]. The identity of the induced mesophase is still unknown, but seems very likely to be columnar [96]. Furthermore, lyotropic nematic phases were obtained in the ternary mixture 51/TNF/linear alkane (the binary mixture 51/alkane did not yield mesomorp-hism). The nematic phase in this system is though to have a columnar nature, namely a nematic columnar phase. 

When a compound exhibits both nematic and smectic phases, then, as a rule, the nematic occurs at a higher temperature. Exceptions to the rule were discovered by Cladis in certain strongly polar materials. The first observations were on binary mixtures of two cyano compounds over a range of composition the sequence of transitions on cooling was as follows. 

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