Liquid crystallinity experimental work

These factors were mentioned soon after the first experimental works on liquid crystalline state of polymers were published. For example, Frenkel considered the effect of these factors by studying the change in the statistical flexibility parameter/ introduced by Flory in his analysis of flexible chain polymers Frenkel proposed the following equation to describe the effect of the type of the solvent on the flexibility of a polymer chain ... 

The rapid growth of the number of publications concerning polymeric liquid crystals indicates that we should expect the appearance of new fundamental studies on the transition of rigid- and semirigid-chain polymers into this state. The range of moderately concentrated solutions for these polymers is studied sufficiently well, while the development of the methods of establishing the liquid. crystalline state in superconcentrated systems and in pure polymers with semirigid chains, as well as the analysis of kinetics of phase transitions, are the subject for further theoretical and experimental works. 

From these and many other studies there was by 1950 plenty of evidence pointing to the possible importance of liquid crystals in tissue. Since then the subject has been explored by direct and experimental methods. My purpose is to examine the chemical forms in which liquid crystals occur and to identify more closely their precise structure and integration into protoplasm and biological fluids. This is often a matter of great difficulty for obvious technical reasons. My own work in this respect has been concerned mainly with lipids and lipoproteins, so I shall refer mainly to these though several other important classes of substances, especially certain proteins and polynucleotides, can exist in the liquid crystalline state and may be present as such in living tissue. 

The zero shear viscosity scales with Nf" to contrast Af dependence for isotropic polymers [20] So far, we have examined the dynamics of rod-Uke macromolecules in isotropic semi-dilute solution. For anisotropic LCP solutions in which the rods are oriented in a certain direction, the diffusion constant increases, and the viscosity decreases, but their scaling behavior with the molecular weight is expected to be unchanged [2,17], Little experimental work has been reported on this subject. The dynamics of thermotropic liquid crystalline polymer melts may be considered as a special case of the concentrated solution with no solvent. Many experimental results [16-18] showed the strong molecular weight dependence of the melt viscosity as predicted by the Doi-Edwards theory. However, the complex rheological behaviors of TLCPs have not been well theorized. 

The existence of pure amorphous bulk polymers has been a controversial issue since the beginning of polymer science. Natural rubber yields an X-ray pattern tiiat contains only amorphous halos, typical of any liquid. Nevertheless, it was difficult for many scientists to believe that molecules with a polymeric chain structure could pack in a truly amorphous way. There are still papers that are submitted for publication that assert that amorphous rubbery polymers are actually composed primarily of microcrystalline domains. This issue has been clarified by the incisive theoretical and experimental work of Flory. It is now understood that there are polymers that exhibit liquid crystalline phases upon melting of the crystals. The nature of the noncrystalline state of pure bulk polymers depends on tiie detailed local structure of the chain and the ratio of die persistence lengtii of die chain to the diameter of the mer. Molecules that are conformationally dexible enough to have a small persistence length can exist in the amorphous liquid state. 

Rods and Helices.—Because of the considerable advances being made in biopolymer characterization, theories and experimental methods particularly applied to stiffened chains and wormlike models, as well as to polyelectrolytes, have continued to proliferate. At the same time work has continued to progress in the synthesis and description of novel synthetic rod-like polymers, many of which have interesting liquid crystalline properties. The publication of the proceedings of a recent conference devoted to the latter materials provides a state of the art description of work in this field. 

It has been reported (Akinay et al. 2001,2002) that the Hartman equation works well for both polymeric solids and melts, including amorphous and crystalline polymers and their blends. Moreover, it also works well in more complicated multiphase systems, such as liquid crystalline polymers (LCPs). Use of the Hartman equation is relatively simple, and its variables can be measured experimentally. Several other equations of state are cited in the Polymer Handbook (Brandrup 1999). Some of these do not permit direct measurement of parameters or contain universal constants that complicate determination of the required parameters. Another advantage of the Hartman... 

Surfactant-water systems show a rich polymorphism and in addition to isotropic solutions and crystals a range of different liquid crystalline phases can form [1,2]. The phase behaviour provides an essential clue to the understanding of the properties of surfactant systems and a large amount of experimental work has been devoted to determine phase equilibria. The theoretical description of the thermodynamic properties of the system has been studied to a much lesser extent. 

Phase transitions involving liquid crystalline phases have been the subject of experimental work for many years. By 1899 Hu-lett [1] had already investigated 4,4 -bis-methoxy-azoxybenzene, 4,4 -bi s-ethoxy-azoxybenzene and cholesteryl benzoate up to 30 MPa. After a long period of inactivity... 

Experimental work In kinetics of polymerization In liquid crystalline media Is sketchy at best. Hopes have been formulated for the possibility of regulating stereo-placements and Inducement of topotactlc effects by free-radical polymerization of liquid crystalline monomers In bulk or In liquid crystalline solvents, due to the high degree of orientational order (35, 52). Such effects have yet to be established. Most of the reported data appear to be due to factors other than molecular orientation and are only Indirectly related to the liquid crystalline order of the medium. For example, factors such as Incomplete miscibility of monomer and solvent, phase separation of the polymer, enhancement of viscosity of the medium, and caging of molecules of initiator (53, 54, 55, 56) can be invoked to explain the observed kinetic effects. 

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