Lyotropic polymer

Extensive DR studies of rod-like polymers in solution covering the isotropic, biphasic and nematic states of solution have been carried out only for two different PAICs in toluene a 1/1 copolymer of n-butyl- and n-nonyl isocyanate (PBNIC) and homopoly(n-hexyl isocyanate) (PHIC). The relaxation process was studied as a function of both concentration and temperature. Only one relaxation process, with a broad distribution of relaxation times, was observed in the isotropic and nematic phases up at relatively low frequencies (10 --10 Hz) (see Fig. 4.15). The most important results are summarized in Fig. 4.16. All three characteristic dielectric parameters—the dielectric increment A8, the maximum of the loss factor 8, and the logarithm of the mean relaxation rate /c—undergo significant changes across the isotropic-biphasic-nematic concentration range. 

The most striking result is that all parameters in the pure nematic phase are a few times smaller in magnitude than in the highly concentrated Isotropic phase. In the isotropic phase both As and s are 

To explain these results, Moscicki proposed a qualitative model of the dielectric relaxation in lyotropic LCPs. A main feature of the model was the assumption that each rod can only undergo spatially restricted rotations (hopping between cages) around the nematic director. To rationalize this situation, the theory of small-step rotational diffusion in a was applied, i.e. it was assumed that the free space available 

The fact that a real system is more or less polydisperse complicates the application of the theory to experimental data. Detailed numerical calculations have shown, however, that the theory correctly explains all the main features of the DR process in PAIC solutions.  

The appearance of liquid-crystalline order in neat liquid-crystalline polymers should have an influence on the chain dynamics. However, since molecular architectures of mcLCPs and scLCPs significantly differ from each other, the extent of this influence is different for each type of PLC. 

First of all, due to a large molecular dipole /x, a field-induced polar order which is proportional to exp iiE/kBT) can be relatively high. This additional field orientation decreases the critical concentration for the formation of the nematic state by the value [240] 

FIGURE 4.42. Field-response times (at a fixed field strength) as functions of temperature for a comb-like acrylic nematic polymer with various molecular mass Mn = 6200 (1), 11,300 (2) [236]. 

In experiment, with a 13% racemic solution of PEG in a mixture of methylene cloride and dioxane elastic moduli measures by a light scattering technique, were [243] 

The smallness of the ratio X22/X11 results in a very interesting peculiarity of the Frederiks transition in homogeneously oriented PEG solution. Instead of the uniform distortion discussed in Section 4.1, a spatially periodic structure is observed [244] with a period of the longitudinal domains 

FIGURE 4.44. Calculated values of the critical field in units (7r/d)(R 22/Ax) for the periodic splay-twist and uniform splay distortions [244]. 

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Lyophobic colloids Lyotropic liquid crystals Lyotropic mesophases Lyotropic polymers Lyral [31906-04-4]... 

Rill, RL Locke, BR Liu, Y Van Winkle, DH, Electrophoresis in Lyotropic Polymer Liquid Crystals, Proceedings of the National Academy of Science, USA 95, 1534, 1998. 

Lyotropic liquid crystals, 15 86, 98-101 amphiphilic molecules in, 25 99-101 Lyotropic mesophases, 20 79 Lyotropic polymer liquid crystals, 25 107-108 Lyral, 2 278 24 486 Lysergic acid, 2 100 Lysergic acid diethylamide (LSD-25),... 

Figure 6 shows the phase diagrams plotting temperature T vs c for PHIC-toluene systems with different Mw or N [64], indicating c( and cA to be insensitive to T, as is generally the case with lyotropic polymer liquid crystal systems. This feature reflects that the phase equilibrium behavior in such systems is mainly governed by the hard-core repulsion of the polymers. The weak temperature dependence in Fig. 6 may be associated with the temperature variation of chain stiffness [64]. We assume in the following theoretical treatment that liquid crystalline polymer chains in solution interact only by hardcore repulsion. The isotropic-liquid crystal phase equilibrium in such a solution is then the balance between S and Sor, as explained in the last part of Sect. 2.2. 

Both polymer melts and polymer solutions sometimes form phases with orientational and positional ordci. Thermotropic polymer liquid crystals possess at least one liquid crystal phase between the glass-transition temperature and the transition temperature to the isotropic liquid. Lyotropic polymer liquid crystals possess at least one liquid cry stal phase for certain ranges of concentration and temperature. 

Lyotropic polymers consisting solely of ring structures are also known, and are exemplified by poly(p-phenylene benzobisthiazole) (IV), which forms a nematic phase in several strongly protonating acids including polyphosphoric acid. Its synthesis and application, like those of the aromatic amide polymers, are discussed later. 

The isotropic-to-nematic transition is determined by the condition [1 — (2/3)TBBWBB/k T] = 0 whereas the spinodal line is obtained when the denominator of XAA is equal to zero. These conditions are evaluated in the thermodynamic limit (Q = 0) in Fig. 7 for a Maier-Saupe interaction parameter Web/I bT = 0.4xAb and for NA = 200, N = 800, vA = vB = 1. When the volume fraction of component A(a) is low, the isotropic-to-nematic phase transition is reached first whereas at high < >A the spinodal line is reached first. In the second case, the macromolecules do not have a chance to orient themselves before the spinodal line is reached. This RPA approach is a generalization of the Doi et al. [36-38] results (that were developed for lyotropic polymer liquid crystals) to describe thermotropic polymer mixtures. Both approaches cannot, however,... 

Unfortunately, there is no report on the detailed physical characterization of these polymers. Such information as unidirectional twist angle and form optical rotation, as well as their dependence on chemical structures and temperature, can be very useful in further understanding the molecular orientations of the polymers in the cholesteric phase. In contrast, a number of studies have been made on the physical-chemical properties of cholesteric lyotropic polymer systems, especially polypeptides. 

Figure 11.2 Chemical structures of some well-studied LCPs. The top four structures are usually used as lyotropic polymers, and the bottom two are thermotropes. Estimates of the persistence lengths (Xp) and effective diameters (d) of these molecules are (Xp, d) = (12,1.04) nm for HPC, (90, 1.5) nm for PBLG. 129.0.6) nm for PPTA. (20.0.6) nm for PBZT. (12.0.6) nm for Vectra A. and (6.0.5) nm for OQO(phenylsulfonyl)10. These values, listed in Baek et al. (1994), Brelsford and Krigbaum (1991), and Farmer et al. (1993), are both solvent- and temperature-dependent, and thus should be used with caution. (From Donald and Windle 1992, with permission from Cambridge University Press.)...

Synthetic supramolecular lyotropic polymer 81 has been prepared from bifunctional molecular components through triply hydrogen bonds [173]. The... 

Lyotropic polymers incorporating heterocyclic structures are also known, e.g.. 

Observed structures of a lyotropic material are classified into three categories nematic, smectic, and cholesteric. Nematic and cholesteric mesophases can be readily identified by microscopic examination. The existence of a smectic mesophase is not well defined and is only suggested in some cases. Solvent, solution concentration, polymer molecular weight, and temperature all affect the phase behavior of lyotropic polymer solutions. In general, the phase transition temperature of a lyotropic solution increases with increasing polymer molecular weight and concentration. It is often difficult to determine the critical concentration or transition temperature of a lyotropic polymer solution precisely. Some polymers even degrade below the nematic isotropic transition temperature so that it is impossible to determine the transition temperatures. Phase behavior is also affected by the polymer molecular conformation and intermolecular interactions. 

The most extensively studied lyotropic polymer is poly-y-benzyl-L-glutamate (PBLG). This polymer exists in solution as a rigid rod-like a-helix. A variety of solvents including dimethylformamide. 

Nonequilibrium electro-optical properties of polymers with mesogenic side groups are also very distinctive. In alternating electric fields, low-frequency dispersion of the Kerr effect is observed. The range of dispersion depends on the molecular weight of the fraction, just as for lyotropic polymers. Fig. 9 shows the dependence of the relative value of the Kerr constant at the field frequency V and at v=0 on the field frequency for solutions of... 

If in a mixture of a lyotropic polymer in a solvent, we replace the solvent partially by a flexible polymer with preferential affinity for the solvent, segregation leads to enclosures of concentrated semirigid polymers. The transition temperature is consequently relatively high (fig. 9). 

Cellulose triacetate-trifluoroacetic acid cholesteric solutions - This kind of lyotropic polymer liquid crystals undergoes a mesomorphic-isotropic phase transition upon heating. The peak is well defined but very small The determination of N for this... 

The three elastic constants of a liquid crystal are important physical parameters which depend on the interaction between the molecules in the liquid crystalline state. While a large number of theoretical and experimental investigations on the elastic constants are contained in the literature for thermotropic liquid crystals, very little is known about them in the case of lyotropic polymer liquid crystals such as those formed by poly-Y-benzyl-L-glutamate (PBLG) in various organic solvents. Some theoretical investigations have been carried out 3 the experimental data is limited largely to measurements of the twist elastic constant and a few recent measurements of the bend and splay constants. ... 

Flow induced phenomena of lyotropic polymer liquid crystals the negative normal force effect and bands perpendicular to shear... 

Lyotropic polymers, barotropic polymers, and thermotropic polymers are merely forming these partially ordered liquids when they are forced into their Uquid ciystalline state. 

The development of liquid crystalline phases and the rheological properties of the lyotropic polymers are discussed in so far as they are related to the formation of... 

These theoretical considerations have led to the following view on a nematic solution, in particular of a solution of a para-aromatic polyamide in sulfuric acid [38]. In a quiescent solution of a lyotropic polymer the chains are more or less aligned parallel inside domains of microscopic size, see Fig. 3. The degree of orientation inside the domain, as represented by the order parameter (Pj), is determined by the concentration and temperature. The excluded volume entropy term leads to the formation of oriented blobs with a size of the order of Lp, the persistence length. These blobs line up due to their anisotropic polarizability, which implies that the formation of the anisotropic phase is governed by a dipole-dipole type of interaction, immediately leading to the Maier-Saupe mean-field potential. The entropy or excluded volume interaction merely tells us... 

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