Mesophases diffusion

The occurrence of the mesophase in the fiber is confirmed by x-ray diffraction examination. The occurrence of three equatorial reflections 010, 110, and 100, the absence of layer and meridional reflections, and the manifestation of the intensity maximum of diffusively scattered radiation at 20 = 19 in the fiber diffraction pattern are the criterion for the presence of the mesophase. The... 

In Vivo Proton NMR Studies in Skeletal Musculature is covered by J. Machann, G. Steidle, C. Thamer, I. Mader and F. Schick this is followed by an account on Quality Assessment of Horticultural Products by NMR from B. P. Hills and C. J. Clark Applications of NMR to Thermostable Proteins is reviewed by E. Alberti, R. Consonni and L. Zetta High Pressure NMR Studies on Lyotropic Lipid Mesophases and Model Biomembrances are reviewed by R. Winter W. S. Veeman discusses Diffusion in a Closed Sphere finally L. Griffiths covers Automatic Analysis of NMR Spectra. It is a pleasure for me to record my gratitude to all of the authors and to the production team for this volume. 

The main feature identifying a cholesteric mesophase in polymers is the presence of optical texture with selective circularly-polarized light reflection. This indicates the formation of 1-helical cholesteric structure in LC copolymers. The X-ray patterns of actually all cholesteric copolymers described (with the exclusion of polymers 3.1 and 4.1, Table 13) correspond to those of nematic and cholesteric low-molecular liquid crystals, which is manifested in a single diffuse reflex at wide scattering angles. At the same time, for copolymers 3.1 and 4.1 (Table 13) small angle reflexes were observed 123), that are usually missing in low-molecular cholesterics. 

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)... 

Addition of a ca. 10% concentration of CA to a mesophase solution (mixture E) of BN quenches completely its photoresolution. CA quenches singlet states of BN in n-hexane at a nearly diffusion-controlled rate (kq = 101- -tf -s- assuming tbn = 3 ns (34-36)). Thus, even In a very viscous medium like cholesteric mixture E, static and dynamic quenching should preclude formation of BN triplets. 

Hubbard PL, McGrath KM, Callaghan PT (2005) A study of anisotropic water self-diffusion and defects in the lamellar mesophase. Langmuir 21(10) 4340-4346... 

Two component hydrogen bonded mixtures of dendrimers and T-shaped branched amphiphiles are also a rich source of mesophases. Figure 13.21 shows a polarised optical microscope image of the contact region between the dendrimer 13.18 and the T-shaped amphiphile 13.19. A wide variety of mesophases co-exist as one component diffuses into another. The majority of these have been identified and studied.13... 

Coalescence of mesophase is often said to be determined by the mesophase viscosity. This aspect requires much further investigation. However, it is clear that, amongst other factors, the rheological behaviour (including viscoelastic effects) of each phase is important in mesophase growth and coalescence. Diffusion of molecular species through the isotropic pitch to the mesophase spheres is likely to be related to the viscosity of the isotropic med i urn. 

While there have been efforts to polymerize other surfactant mesophases and metastable phases, bicontinuous cubic phases have only very recently been the subject of polymerization work. Through the use of polymerizable surfactants, and aqueous monomers, in particular acrylamide, polymerization reactions have been performed in vesicles (4-8). surfactant foams ), inverted micellar solutions (10). hexagonal phase liquid crystals (111, and bicontinuous microemulsions (121. In the latter two cases rearrangement of the microstructure occured during polymerization, which in the case of bicontinuous microemulsions seems inevitable b ause microemulsions are of low viscosity and continually rearranging on the timescale of microseconds due to thermal disruption (131. In contrast, bicontinuous cubic phases are extremely viscous in genei, and although the components display self-diffusion rates comparable to those... 

We will assume the mesophase director to be parallel to the direction of the static magnetic field. In the last section, III.E, the no-inertia assumption will be rejected and the diffusion operator (2.6) replaced with the complete Hubbard operator. We shall investigate the spectroscopic effects of molecular inertia in the case of an axially symmetric g-tensor. 

The two algorithms already developed and used to reproduce ESR line-shapes of paramagnetic species in free diffusion are applied in this subsection to the case of spin probes dissolved in liquid crystalline mesophases. The main point of diffoence with the previously examined cases is due to the introduction of an orienting potential v ose nature is directly reflected in the structure of the Fokker-Planck opoator, whidi in the difiusional assumption is given by Eq. (2.6). The explicit form of the potential we use in this... 

As mentioned in the introduction, the director potential of the mesophase is assumed to have the same direction as the external static magnetic field. The Hamiltonian describing these spin systems is given by Eq. (3.5). To adapt the CFP already iqiplied to these systems in the free diffusion case to the present case, some small modifications have to be made. These minor changes concern the step where the c(n + 1), coefficients and the s moments... 

Cholesteric mesophases in general resemble the nematic mesophase when observed by both small-angle X-ray diffraction, SAXD, and WAXD. The smectic mesophase, in contrast, produces both diffuse rings at 4--5 A and sharp rings at a distance generally, but not necessarily, equal to the repeat length of the monomer unit, between 15 and 50 A. 

Solid formulations for sustained drug release may contain mesogenic polymers as excipients. The mesogenic polymers form a matrix, which is usually compressed into tablets. Some of the most frequently used excipients for sustained release matrices include cellulose derivatives, which behave like lyotropic liquid crystals when they are gradually dissolved in aqueous media. Cellulose derivatives such as hydroxy-propyl cellulose or hydroxy-propylmethyl cellulose form gel-like lyotropic mesophases in contact with water, through which diffusion takes place relatively slowly. Increasing dilution of the mesophase with water transforms the mesophase to a highly viscous slime and then to a colloidal polymer solution. 

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