Lyotropic nematic polymers

The viscoelastic constants of the lyotropic nematic polymer poly-y-benzyl glutamate was measured by Taratuta et al. [70]. Santos and Durand [71 ] measured order and mi-... 

Woo the temperature dependence of pitch for chiral nematic polymers does not seem to follow any particular pattern. It is believed that as temperature is increased, specific interactions, e.g., hydrogen bonding, whether inter- or intramolecular or polymer-solvent interactions are destroyed. The polymer chains become more flexible and the side groups more easily relaxed, thereby changing the physical properties of the chiral nematic structure. Similarly, an increase in concentration leads to a decrease in pitch for most lyotropic cellulosic liquid crystals with the exception of cellulose tricarbanilate (CTC) in ethyl methyl ketone, 2-penta-none, or tiiethylene glycol monoether and the chlorophenyl urethane derivative in diethylene glycol monoether. ... 

The precipitation process is assumed to lead either from the lyotropic, nematic liquid crystalline state via predpitation with water under maintenance of ordered water-polymer layers to the crystal form II, or with other solvents (and also from low polymer concentrations with water) through disordered solvent-polymer structures to crystal form I In both crystal structures the ultimate polymer crystal layers are H-bonded in the aystallographic bc-plane (100), as shown in Fig. 6.2. In crystal form 1 the second molecular chain goes through the center of the unit cell (Pn or P2j/n space group, 2 chains per unit cell, monoclinic, pseudo-orthorhombic)... 

Solution properties indicate that the metal-poly(yne)s exist in a rod-like structure. They display lyotropic nematic mesophases [30] and form crystallites with a diameter of up to 50 nm [31]. Absorption and luminescence spectra of the polymers show that 7t-electron conjugation is expanded over the whole polymer chain, and third-order non-linear optical properties are exhibited. For polymer 7 good photocurrents were found in sandwich-diodes. 

Analogous ochre-yellow polymers 4.26 that contain thiophene in the main chain (Mw= 11,300-35,300 PDI = 1.5-2.7) have also been prepared [61]. Upon slow concentration of their solutions in chlorinated solvents, such as chloroform, lyotropic nematic liquid-crystalline phases form. In one case, a lyotropic smectic state was identified. 

Therefore the formation of a lyotropic nematic mesophase is possible for polymer/surfactant aggregates. Examples of lyotropic nematic behavior will be presented in the next section for PANi/camphorsulfonic acid aggregates. 

Nematic polymers have much in common with conventional, low-mass nematics. Their behavior in an electric field is usually described in the firame-work of the same Leslie-Ericksen approach though, strictly speaking, some corrections must be done in the set of nematodynamic equations to take into account the coupling between the motion of mesogenic units and the backbone of a polymer [228]. The field behavior of thermotropic nematic polymers differs considerably from that of lyotropic solutions of long rodlike molecules (like poly-7-benzyl-glutamate) and the two systems will be discussed separately (see also a recent review article [279]). 

Most often the lyotropic LC polymers form nematic mesophases. Most of the polymers in this class are aromatic polyamides with aromatic ring structures, as shown in Thble 7.1 (7). Several of the polymers in Table 7.1 form very high-modulus fibers see Chapter 11. The fibers are crystalline after formation. 

By Heck-type coupling liquid crystalline rigid-rod polymers containing [1,3-(diethynyl)cyclobutadiene] cyclopentadienyl moieties were prepared [202]. One example is the reaction of the diethynyl derivative 41 with a 2,5-diodothiophene 42 to the polymer 43 [equation (21)] which show lyotropic nematic phases. 

LUE Luehmaim, B., Finkelmann, H., and Rehage, G., Phase behavior and structure of polymer surfactants in aqueous solutioa The occurrence of lyotropic nematic phases, Makromol. Chem., 186,1059,1985. 

Figure 11 demonstrates the application of deuteron NMR spectroscopy on sheared samples with the simultaneous measurement of the viscosity to two different nematic polymer systems. The different behavior of these systems is apparent from the data one system is flow-aligning, the other system is tumbling. The Leslie eoefficients and 3 obtained for the shear-aligning system are both negative, whereas and 3>0 for the tumbling system. Deuteron NMR has also been employed to study the director orientation of lyotropic lamel-... 

The available experimental material on the processes which take place in lyotropic nematic systems is very limited. The set of different values of the moduli of elasticity ATn, K22, and K -, obtained in one experiment [54] for solutions of PBG in dioxane with addition of trifluoroacetic acid, should apparently be considered especially approximate due to the possible error in the measurement of the anisotropy of the susceptibility mentioned above. As the theoretical calculations in [58] showed, the elasticity coefficients of the polymeric lyotropic nematic are a function of the degree and mechanism of flexibility of the individual polymer chain. Although all moduli should be of the same order of magnitude for rods and freely jointed chains (but should be slightly higher... 

Solution spinning is a widespread and attractive route for the production of polymer fibres, and has been applied to a variety of CNT systems. Aparticularly interesting possibility is the use of a lyotropic nematic nanotube solution as a route to a highly aligned fibre. Much of this work is directed at high loadings of nanotubes and examples include the use of surfactant-stabilised dispersions of CNTs injected into a PVA or poly(ether imide) (PEI) bath, to form a fibre that can be handled and drawn, and the use of pure SWCNT dispersions in superacid . 

Note 5 If the mesogenic side-groups are rod-like (calamitic) in nature, the resulting polymer may, depending upon its detailed structure, exhibit any of the common types of calamitic mesophases nematic, chiral nematic or smectic. Side-on fixed SGPLC, however, are predominantly nematic or chiral nematic in character. Similarly, disc-shaped side-groups tend to promote discotic nematic or columnar mesophases while amphiphilic side-chains tend to promote amphiphilic or lyotropic mesophases. 

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