Liquids, anisotropic

Surfactants having an inverted tnmcated cone shape yield inverted spheroidal micelles. Many double-chain surfactants such as AOT fonn such inverted micellar stmctures. These kinds of surfactant also fonn inverted anisotropic liquid crystalline phases. 

If one follows the solution viscosity in concentrated sulfuric acid with increasing polymer concentration, then one observes first a rise, afterwards, however, an abrupt decrease (about 5 to 15%, depending on the type of polymers and the experimental conditions). This transition is identical with the transformation of an optical isotropic to an optical anisotropic liquid crystalline solution with nematic behavior. Such solutions in the state of rest are weakly clouded and become opalescent when they are stirred they show birefringence, i.e., they depolarize linear polarized light. The two phases, formed at the critical concentration, can be separated by centrifugation to an isotropic and an anisotropic phase. A high amount of anisotropic phase is desirable for the fiber properties. This can be obtained by variation of the molecular weight, the solvent, the temperature, and the polymer concentration. 

Optically anisotropic liquid-crystal displays consisting of triphenylene, (IV), were prepared by Ushiyama et al. (4) and used in optical compensatory film. 

The thermodynamic investigations have indicated that the glass transition is a freezing-in process. Consequently the anisotropic liquid crystalline orientation of the mesogenic side chain should also freeze in, yielding an anisotropic glass having a liquid crystalline structure. This process is of interest in view of the applicability of l.c. polymers. 

Figure 6. Phases for systems which give I, crystal, anisotropic liquid, and isotropic liquid II, crystal and isotropic liquid III, crystal, cubic plastic crystal, and isotropic liquid (8)...

Figure 7. Close to the PIT value two phases with a lamellar structure exist. One of these, the surfactant phase (S), is an isotropic liquid, the other one, (N), is an optically anisotropic liquid crystal with a lamellar structure.

Discussion. We can now propose a coarse description of the paraffinic medium in a lamellar lyotropic mesophase (potassium laurate-water). Fast translational diffusion, with D 10"6 at 90 °C, occurs while the chain conformation changes. The characteristic times of the chain deformations are distributed up to 3.10"6 sec at 90 °C. Presence of the soap-water interface and of neighboring molecules limits the number of conformations accessible to the chains. These findings confirm the concept of the paraffinic medium as an anisotropic liquid. One must also compare the frequencies of the slowest deformation mode (106 Hz) and of the local diffusive jump (109 Hz). When one molecule wants to slip by the side of another, the way has to be free. If the swinging motions of the molecules, or their slowest deformation modes, were uncorrelated, the molecules would have to wait about 10"6 sec between two diffusive jumps. The rapid diffusion could then be understood if the slow motions were collective motions in the lamellae. In this respect, the slow motions could depend on the macroscopic structure (lamellar or cylindrical, for example)... 

Static quadrupole effects in NMR are observed in solids (9) and also in anisotropic liquid crystals (10, 11, 12). For nuclei with spin quantum numbers, I, greater than V2, the distribution of positive charge over the nucleus can be nonspherical and the situation can be described in terms of a nuclear electric quadrupole moment. The interaction between the quadrupole moment, eQ and electric field gradients, eq, shifts the energy levels of the nuclear spin states. 

Polv(ether) Synthesis. The poly(ethers) were made by a two-phase reaction with dibromoalkanes. In a typical reaction, 0.75 g (2.4 mmol) of (II, R=H)) was mixed with 70 ml of 2N NaOH in a 3-necked round-bottom flask equipped with a mechanical stirrer. To this was added an equimolar amount of 1,9-dibromononane in 20 mL nitrobenzene and approximately 10 mg of tetrabutylammonium iodide and the mixture was stirred overnight at 50°C. The resulting solid mass was washed with methanol and then with 2N NaOH. After washing with 0.1 N HC1, the product was Soxhlet-extracted with methanol and dried to yield 0.68g (64.7%) of a light green powder which melted to an anisotropic liquid at 290°C. The other poly(ethers) were prepared in the same manner, using spacer lengths of 7, 9,11, 7/9 mixture, and 9/11 mixture. The yields and IR spectra of the poly(ethers) is shown in Table I. 

The model of a dipole in a spherical cavity can only provide qualitative insights into the behaviour of real molecules moreover, it cannot explain the effect of electrostatic interactions in the case of apolar molecules. More accurate predictions require a more detailed representation of the molecular charge distribution and of the cavity shape this is enabled by the theoretical and computational tools nowadays available. In the following, the application of these tools to anisotropic liquids will be presented. First, the theoretical background will be briefly recalled, stressing those issues which are peculiar to anisotropic fluids. Since most of the developments for liquid crystals have been worked out in the classical context, explicit reference to classical methods will be made however, translation into the quantum mechanical framework can easily be performed. Then, the main results obtained for nematics will be summarized, with some illustrative... 

Expressions for the resistance coefficients of a particles in an anisotropic liquid can be found in papers by Tskhai and Pokrovskii (1985) and by Pokrovskii and Tskhai (1986). 

Pokrovskii VN, Tskhai AA (1986) Slow motion of a particle in slightly anisotropic liquid. 

Tskhai AA, Pokrovskii VN (1985) Rotational mobility of non-spherical particle in anisotropic liquid. Kolloid Zh 47(1) 106-111... 

A number of important process parameters were investigated to find out their effect on pitch characteristics and yield of the toluene and quinoline insolubles. The pitches produced were characterized by solvent analysis, NMR, thermal, and elemental analysis. Insolubles in toluene, pyridine and quinoline were used because these fractions represent the fusable and infusable anisotropic liquid crystal fraction formed in the pitch. 

If the cylinders are at some angle j> to one another, then there is a large volume surrounding the rod where the approaching rod s centre-of-mass enters. If, however, the rods are oriented parallel to one another there is little volume that is excluded. This gives rise to an effective potential of the form IkTDL2(sin fi). It leads in a virial expansion to a critical volume fraction [Pg.637]

Following the technological breakthroughs which led to the discovery of (1) the liquid crystalline behavior ofpara-oriented aramids26 and (2) a novel method for spinning anisotropic liquid crystalline polymer solutions,27 Kevlar aramid fiber was produced and commercialized by the DuPont company in 1972. Other fibers based on aromatic polyamide compositions, which were produced and commercialized by other companies, were Technora (Teijin, Japan), Teijinconex (Teijin, Japan), andTwaron (Akzo, The Netherlands). Additionally, SVM is a fiber produced in the Former Soviet Union and it was announced in 1990 that a new aramid fiber had been introduced by Hoechst, in Germany. 

J. Jokisaari, NMR of Noble Gases Dissolved in Isotropic and Anisotropic Liquids, Progr. NMR Spectr., 26 (1994), 1-26. 

H. D. Dardy, V. Volterra, and T. A. Litovitz. Rayleigh scattering Orientational motion in highly anisotropic liquids. J. Chem. Phys., 59 4491-4500 (1973). 

These results point out the value of the weak cooperative interaction between the dopant molecules and the anisotropic liquid crystalline environment. The reason for the sharp drop in with increasing temperature in the nematic region is unclear at this point. Competing equilibria involving molecular association combined with temperature-dependent relaxation processes may have something to do with it. These effects were not observed in the isotropic system discussed earlier. 

One of the few exceptions are molecules like p-azoxyanisol, p-azoxyphenetol and anisaldazine, which form anisotropic liquids and for which Wolf [Physik and Chemie der Grenzjlachen. Vol. 1, Springer (1957), p. 44) reports y T) curves with kinks. 

In general, however, rotation and translation of the molecules are degrees of freedom which are acquired simultaneously on fusion, although sometimes only translational freedom is acquired. This happens, for example, in the case of very long molecules where rotation is prevented by steric factors (anisotropic liquids), and also when the intermolecular forces are powerful and anisotropic as for associated liquids. In these instances the freedom of rotation is achieved progressively as the temperature is raised above the melting point. This is in contrast to spherical molecules which, because of their shape and the symmetry of their force fields, begin to rotate freely in the solid state. 

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