Viscous isotropic phase

Dynamic polymers having C=N bonds responding to changes in a neat/solution environment were reported by Lehn et al. [22]. Polymers 9-12 were synthesized by the corresponding dialdehydes and diamines in the presence of anhydrous Na SO (Fig. 8.3). The isotropic transition temperatures of polymers 9 and 10 were obtained at 72.5 and 68.4°C, respectively. Polymer 11 was not a film or solid but viscous oil with an isotropic phase at less than 40°C. In contrast, polymer 12 showed the highest isotropic transition temperature at about 160°C due to the existence of... 

L micellar solution phase L lamellar liquid crystalline phase V viscous isotropic phase H2 reverse hexagonal phase... 

At relatively low concentrations of surfactant, the micelles are essentially the spherical structures we discussed above in this chapter. As the amount of surfactant and the extent of solubilization increase, these spheres become distorted into prolate or oblate ellipsoids and, eventually, into cylindrical rods or lamellar disks. Figure 8.8 schematically shows (a) spherical, (b) cylindrical, and (c) lamellar micelle structures. The structures shown in the three parts of the figure are called (a) the viscous isotropic phase, (b) the middle phase, and (c) the neat phase. Again, we emphasize that the orientation of the amphipathic molecules in these structures depends on the nature of the continuous and the solubilized components. 

Amphiphilic Cubic Mesophases Viscous Isotropic Phases. In Figure 1, at positions where a high concentration of globular micellar forms might be expected, the cubic viscous isotropic mesophases Sic, Vi, and V2 are encountered. This is further illustrated by Figure 5. These mesophases, because of their inclusion within the general sequence of amphiphilic mesophases ... 

The aggregates discussed above are all anisodimensional, which is the reason for the anisotropic character of the mesophases. In some systems it has been possible to prove the existence of isotropic highly viscous phases of similar structure but which clearly consist of almost isodimensional aggregates. The exact structure of these phases is still the subject of discussion, as is also the case with the complex mesophases. The relation between the isotropic phases and globular proteins and plastic crystals of non-amphiphilic substances has been discussed by Gray and Winsor (5). 

Here rj = v IcbT/ 0D is the viscosity of the (hypothetical) isotropic phase at C. The viscous stress, 10(v/v )7j jSyD (uuuu), contributes to the Leslie viscosities, as follows (Larson 1996) --------------------------------------------------------------------... 

The cubic phase is still a rather rare observation in thermotropic liquid crystal systems, and is foimd in conventional calamitic materials, as well as in polycatenar materials vide infra). It is a viscous, optically isotropic phase whose kinetics of... 

The closed loop is not the only characteristic of the nonionic surfactant-water binary phase diagram. Like the ionic surfactant-water mixture, nonionic surfactants, at higher concentration in water, exhibit lyotropic mesophases. Figure 3.14 shows a typical binary phase diagram exhibiting the full lyotropic mesophase sequence II, cubic isotropic phase HI, direct hexagonal phase (middle phase) VI, special cubic ( viscous phase) La, lamellar phase (neat phase). Note the presence of the two-phase domains surrounding each mesophase, the critical point on top of each, and the zero-variant three-phase feature. 

At the time of this writing, the most immediate application for the surfaces discussed in this section is to provide models for viscous isotropic phase liquid crystals and certain phase-segregated polymer blends and block copolymers. In this subsection, we show how to calculate diffraction peak intensities from a class of model structures based on these surfaces. The method applies to scattering-density profiles (electron densities for x-ray scattering) determined by ... 

A third lyotropic mesophase which occurs frequently in surfactant-water systems is normally designated viscous isotropic. This phase is very viscous, sometimes brittle, but unlike neat and middle it is not bire-fringent. The structure of the viscous isotropic phase is still not known with certainty. In some systems x-ray studies have indicated that the structure consists of spherical units packed in a face-centered arrangement 4, 22). It has been proposed that the polar groups of the molecules cover the outside surfaces of the spherical units and that the hydrocarbon chains are essentially liquid in their arrangement inside the units. In this respect the structure is similar to one of the proposed middle phase structures (4). As in the other lyotropic phases, the solvent probably fills the voids among the spherical units of surfactant. 

Positive statements relating the structure of the viscous isotropic phase to the high resolution spectra are difficult to make. It is evident, because of the large differences between the spectra of this phase and the middle... 

Figure 18. The 60-MHz spectrum of viscous isotropic phase of DC12AO Obtained at 32°C. on a Varian A-60 spectrometer and calibrated with respect to external. TMS...

Obviously the viscous isotropic phase is easily distinguished from the neat and middle phases by means of its NMR characteristics. 

Hahn echo sequences work regardless of the relative phases of the two pulses so that the solid echo sequence (7i/2)Q-x-(7i/2)gQ can induce Hahn echoes in an isotropic non-viscous liquid as well as the echoes from two identical n/2 pulses. Therefore, two different contributions to an echo can exist for the solid echo in a sample like a liquid crystal which has both a liquid and solid character (Cohen-Addad, 1974 Cohen-Addad, and Vogin, 1974). 

In hydrophobe-dominated compositions, such as aerosol OT-water systems, inverted middle and inverted viscous isotropic phases can occur in which the tails point outward towards the hydrophobic medium while water is trapped inside. ... 

Zwitterionic surfactants broadly resemble nonionic materials but because two bulky charged groups are involved the head groups are large. An exception is dimethyldodecyl amine oxide [146] which has a compact head group. This forms Hj, Vj and Emphases. The Hi (termed middle phase in this paper) exists between 35 and 65% surfactant and from <20°C to >105 °C. The Vi (viscous isotropic) phase has a narrow range... 

The cubic phases are also known as viscous isotropic phases - because they are As the name implies, these phases have structures based around one of several possible cubic lattices, namely the primitive, face-centred and body-centred. There are two very distinct aggregate structures, i.e. one comprised of small micelles, normal or reversed, and one based on three-dimensional bicontinuous aggregates. The normal and reversed structures that occur for both make a total of four classes. It is still not certain exactly which structures can occur for the different classes, but the overall picture has become much clearer during the past few years (46, 49-57), with more and more structures being identified. The first set of structures comprised of small globular micelles is labelled I , while the second group, the bicontinuous three-dimensional (3-D) micellar network, is labelled V . 

In the following, both Ak and k aure considered as model parameters. The first one is essential for the coupling between the alignment and the viscous flow. The second one influences the orientational behavior quantitatively but does not seem to aifiect it in a quaditative way. If one wants to correlate the present theory with the flow behavior of the alignment in the isotropic phase, on the one hand, and in the nematic phase, on the other hand, for small shear rates where the magnitude of... 

A transition from a LC phase to an isotropic phase can still be observed in the case of networks with poor crosslinking density. These systems can actually be considered as highly viscous liquids in the LC state, as proposed by Finkelmann (16) they are therefore expected to exhibit such a transition. In the case of networks with higher crosslinking density, the molecular organization, typical of the LC phase is locked by the crosslinks. Therefore, no clearing temperature can be observed, and this ordered structure can be destroyed only upon thermal decomposition. 

I), then a hexagonal phase (zone III), and finally a micellar phase (zone IV). As NaC is added to sodium oleate, the lamellar phase (zone I) disappears abruptly, showing that very little bile salt can be incorporated into the lamellar liquid crystalline phase formed by sodium oleate. At low concentrations of water, a viscous isotropic phase having a cubic lattice by X ray is present (zone II). There is a large zone of hexagonal liquid crystalline phase (zone III) which can contain up to 65% NaC by weight. This phase has been studied by X-ray diffraction at a constant 40 % water, and the distance between... 

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