Polymers in the Liquid Crystalline State

A detailed insight into the freezing-in process is given by optical investigations. As described in 2.3.1.4 for nematics, 2.3.2.3 for cholesterics and 2.3.3.3 for smectics, the optical uniaxial character of the polymers in the liquid crystalline state has been proved by birefringence measurements and the state of order was calculated from these measurements. This method also provides information about the glassy state. For conventional l.c s it has been demonstrated, that the temperature dependence of... 

Wissbrun, K., Rheology of rod-like polymers in the liquid crystalline state, J. Rheol., 25, 619-662(1981). 

In contrast, other X-ray patterns obtained from linear polymers in the liquid crystalline state are characteristic of a disordered lamellar structure 103 c, 105, 106) They pre-... 

For an introductory account of LCP s including references to more detailed information, see the review article on "Rheology of Rod-like Polymers in the Liquid Crystalline State" by author, J. Rheology 25, 619 (1981). (The bibliography of this paper is appended for reference. 

Wissbrun, K. R, Rheology of Rod-Like Polymers in the Liquid Crystalline State, J. Rheol, 25, 619-662, 1981. 

The ion conductivities of a range of TPEOCELL complexes with LiCFsSOs were examined by AC impedance spectroscopy from 293-373 K, so that all the complexes remained in the liquid-crystalline state during the measurements [235]. The inorganic salt concentration, indicated by the molar ratio of lithium ions to oxygens in the polymer chain, [Li]/[0], ranged from 0.038 to 0.125. The bulk conductivities were 10-6 Son-1 at ambient temperatures... 

Let N cylindrical rods be situated in volume V, their concentration being c = N/V. The polymer volume fraction in the solution is then - jrpcd V4. Let us introduce the orientational distribution function for the rods f(u) cf(u)df2 is the number of rods per unit volume, which have the orientations within the small spatial angle dQ around the unit vector u. It is dear that in the isotropic state f(u) = const = l/4a. In the liquid-crystalline state the function f(u) has two maxima along the anisotropy axis. 

The order must then be frozen in before crystallisation occurs, since this would result in the formation of grain boundaries and a reduction in transport or emission efficiency. Device breakdown is also a possibility. The most efficient way to fix the liquid crystalline order is the formation of anisotropic networks by the polymerisation of reactive mesogens in the liquid crystalline state.Anisotropic polymer networks formed from the thermal or photoinitiated polymerisation of polymerisable, so-called photoreactive, liquid crystalline monomers have been used in a wide variety of electrooptic applications, see Chapter This is a more attractive approach than cross-linking... 

If a polymer is incapable of crystallizing or if it has retained non-crystalline form for kinetic reasons, it still remains in the liquid crystalline state in the entire region of temperatures and concentrations below curve 1 and not only between curves 1 and 2. The point Vj T " corresponds to the limiting concentration and limiting temperature for the existence of liquid crystalline state of the polymer. 

Liquid crystalline compounds are remarkable because of their ability to show spontaneous anisotropy and readily induced orientation in the liquid crystalline state. When polymers are processed in the liquid crystalline state, this anisotropy may be maintained in the solid state and can readily lead to the formation of materials of great strength in the direction of orientation. A particularly important example of the use of this property for polymers is in the formation of fibers from aromatic polyamides which are spun from shear oriented liquid crystalline solutions Solutions of poly(benzyl glutamate) also show characteristics of liquid crystalline mesophases, and both of these types of polymers are examples of the lyotropic solution behaviour of rigid rod polymers which was predicted by Flory... 

In the polymers of Roviello and Sirigu discussed above, the chain direction was perpendicular to the layers, yet the fully extended repeat unit of the polymer with mesogenic structure 2 had a length of approximately 29 A while a spacing of only 20.6 A was observed These examples indicate that the spacer may not always be completely extended in the liquid crystalline state, but the spacer is certainly much more extended than if it were in a random coil configuration. 

The best vesicle stabilization effect was obtained by polymerization of buta-diyne units within the hydrocarbon chains of amphiphiles after the vesicle was formed. This polymerization produces red or blue polyenes and occurs only if the vesicle membrane is in the liquid crystalline state. No polymers formed... 

At 80°C, the polymers with more than 10 carbon atoms are in the liquid crystalline state. Low mobility of the side chain prevents the polymers of n 9 to be in the thermotropic liquid crystal. The existence of the discontinuity is evidence for the solvent like nature of the side chains in the thermotropic liquid crystalline phase. 

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