Phase separation in liquid crystalline

The phenomenon of phase separation in liquid crystalline polymer solutions has been the subject of recent interest. This phenomenon was noticed in a number of lyotropic liquid crystal... 

Polymer addition induces phase separation in liquid crystalline... 

However, understanding the thermodynamics of phase separation in liquid crystalline block copolymers is in its infancy. The morphology of such block copolymers will be influenced by the competition between... 

Gee RFI, Lacevic N, Fried LE (2005) Atomistic simulations of spinodal phase separation preceding poiymer crystaiiization. Nat Mater 5(l) 39-43 Gupta AM, Edwards SF (1993) Mean-field theory of phase transitions in liquid-crystalline polymers. J Chem Phys 98(2) 1588-1596... 

Liquid crystals have found widespread use as stationary phases in gas chromatographic applications due to the benefits of coupling the usual analytical strengths of gas chromatography with the unique structure and shape selective properties of the liquid crystalline phase. Interaction of solutes with the orientational order provided by the anisotropy of the liquid crystal stationary phase allows for the effective and selective separation of positional and geometric isomers. This remarkable solute structural discrimination is especially important for the separation of isomers that have similar physical properties and thus cannot be conveniently separated on conventional capillary columns that mainly differentiate on the basis of boiling point/molecular weight or polarity differences. The mechanism of separation in liquid crystalline stationary phases is based on specific intermolecular inter-... 

To elucidate the spatiotemporal emergence of crystalline structure and liquid-liquid phase separation in the crystalline-amorphous polymer blends, Rathi (80] employed the time dependent Ginzburg-Landau (TDGL Model-C) equations pertaining to the conserved concentration order parameter and the noncrystal order parameter. Model C is a combination of TDGL Model-A and Model-B, viz. ... 

If there are included among the diluents mixed with the crystalline polymer some which are sufficiently poor solvents, the phase diagram may then exhibit liquid-liquid phase separation, in addition to the liquid-crystal boundary curve. Examples are shown in Figs. 133... 

The SD is a phase separation process usually occurring in systems consisting of more than two components such as in solutions or blends. However, in the present case the system employed is composed of one component of pure PET. In this case, what triggers such an SD type phase separation Doi et al. [24, 25] proposed a dynamic theory for the isotropic-nematic phase transition for liquid crystalline polymers in which they showed that the orientation process... 

The objective of this review is to characterize the excimer formation and energy migration processes in aryl vinyl polymers sufficiently well that the excimer probe may be used quantitatively to study polymer structure. One such area of application in which some measure of success has already been achieved is in the analysis of the thermodynamics of multicomponent systems and the kinetics of phase separation. In the future, it is likely that the technique will also prove fruitful in the study of structural order in liquid crystalline polymers. 

The above phases represent the most common phases used in solving nearly all of the frequently encountered application problems. There are many other stationary phases which are produced to tune the phase polarity for specific applications. In addition to these phases, there are liquid crystalline, chiral, cyclodextrin, polymers such as polystyrene, divinylben-zene, molecular sieves, and alumina, which are designed for specific separation problems. The chemistry of fused silica deactivation and stationary-phase application, bonding, and cross-linking has been reviewed in detail [3,4]. 

For a phase-separated region to exist, lipids have to move into and out of various phases. The lateral diffusion constant in liquid crystalline bilayers is about l(T8cm2/s, which corresponds to an exchange frequency between lipid-lipid nearest neighbors of about 106/s. A necessary precondition for the detection of phases by NMR technique is that the proportion of observable species in the phase is sufficiently large. 

Finally, we consider the method for anisotropic ionic conductivity. Anisotropic ionic conductivity is a phenomenon that appears in a sample undergoing liquid crystalline phase or micro phase separation. In the nanotechnology field such samples are expected to yield important materials because they can raise the value of ion conduction. To measure the anisotropic ionic conductivity, one has to design a special cell. Figure 6.5 shows an example of a cell shaped Uke a comb [8]. In the comb-shaped cell, the ionic conductivity is measured between two teeth of the comb. As the liquid crystalline molecules orient perpendicularly on the glass substrate, the ionic conductivity is obtained along with the minor axis. The important task is to prepare the specific phase homogeneously in the measurement cell. The details will soon be presented in published papers. 

Other rate processes studied include isopropyl group rotation, (529) restricted rotations in phosphine derivatives of cyclopentadienyl complexes of iron and nickel, (530) and ring and nitrogen inversion in (en) complexes of praseodymium. (531) Molecular geometries of molecules in solution can be accurately determined from NMR spectra of the molecules oriented in a nematic phase of a liquid crystalline solvent. The effect of Eu(dpm), on the nematic phase spectrum of pyridine has been examined. The pyridine geometry is unaffected by the LSR. The observed LIS values can be separated into isotropic and anisotropic components. (532)... 

Dumaual AC, Jenski LJ, 8tillwell W. Liquid crystalline/gel state phase separation in docosahexaenoic acid-containing bilayers and monolayers. Biochim Biophys Acta 2000 1463 395-406. 

Interestingly, the phase separation in this case results from a change in the composition of the reaction mixture rather than temperature or pressure. The iridium catalyst was found to be sufficiently soluble for catalysis in the form of the substrate complex, but it was precipitated quantitatively once all substrate has been consumed. Supercritical fluid extraction at that stage yielded the solvent- and metal-free product in crystalline form, leaving the active and selective catalyst behind for further use. Under batch operation, noticeable deactivation occurred after the fourth cycle, but this might be avoided by working in a closed system. Recently, ionic liquids have been found to stabilize the iridium catalyst for better recycling in a two-phase approach [30]. 

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