Lyotropic behavior

Both thermotropic and lyotropic behavior In a large variety of solvents are found. 

Non-covalent thermotropic liquid crystal dendritic systems have been achieved recently by converting the amphiphihc surface of the dendrimers (-NH2) into a hydrophobic shell (alkanoate chains). Tomalia et al. reported on the non-aqueous lyotropic behavior of supramolecular complexes re-... 

Under basic synthesis conditions, the same type of surfactant Rn(n = 10, 8,6,4) led to the formation of MCM-41, and only the long-spacer surfactant R12 yields SBA-8. This result is in agreement with the lyotropic behavior of long, rigid-chain surfactants. 

Freeze-fracture reveals intravesicular details in three dimensions. Samples are frozen rapidly in liquid nitrogen and fractured to reveal internal structure. Additionally, lyotropic behavior of amphiphilic ABA triblock copolymers in water has been investigated using polarized light optical microscopy and freeze-fracture TEM [188],... 

Napoli A, TireUi N, Wehrli E, HubbeU JA (2002) Lyotropic behavior in water of amphiphiUc ABA triblock copolymers based on poly(piopylene sulfide) and poly(ethylene glycol). Langmuir 18 8324-8329... 

The substituted polyamides with long alkyl- and alkoxychains [33] are highly soluble and form anisotropic melts above their melting temperature. These polyamides are typical examples of sanidic liquid crystalline polymers. Generally, no lyotropic behavior is observed. The temperature stability is obviously substantially lowered due to the substitution with alkyl chains. 

Some other compounds may also have the potential to possess amphotropic behavior, but because of too high melting points these properties can not be observed, for example polyamides such as Kevlar show lyotropic behavior only, and are not discussed here. Furthermore, one has to take into account... 

The lyotropic behavior of these carbohydrate derivatives has been studied very carefully [96]. It follows the classical sequence of mesophases established for the ionic detergents such as soaps. In contact preparations of l-0-octyl-/3-D-glucopyranoside (10 e) with water at room temperature three types of lyomesophases are observed (from high to low amphiphile concentration) lamellar, cubic and columnar hexagonal, their principal structures are depicted in Fig. 12. 

Lyotropic behavior of simple metal carboxylates has been described earlier (Section 7.9.9). However, many alkaline earth metal salts of dodecylbenzenesulfonates (Mg , Ba , and Ca ), as well as those of Hg , Pb , Al , Mn , Co", Ni", Cu", Cr , and Fe , have also been reported to form Lq, phases in water. At higher surfactant concentrations, another mesophase, with a poorly defined structure, was induced for some salts. 

For the formation of a lyotropic phase in solutions, the critical parameter is the ratio of Ip/D (the aspect ratio ). Predictions for semi-flexible cylinders with hard-core interaction have revealed that the ratio Ip/D should be of the order of 10 to introduce a lyotropic behavior at reasonable concentrations [151]. The driving force for ordering phenomena in the bmsh solutions is the excluded volume interactions. In contrast to flexible cyhnders with hard-core interactions, the CPBs - at least their side chains - begin to interpenetrate when the threshold concentration (which can be rather low for brushes with long side chains) is exceeded. With a further increase in the concentration above the threshold, the excluded volume interactions will gradually diminish, such that the lyotropic behavior would be expected to disappear again at somewhat higher concentrations [152]. 

PCBZL + m-cresol at room temperature is known to be in a random coil, and undergoes an inverse coil-helix transition as the temperature is raised [30]. The observation of lyotropic behavior in PCBZL + m-cresol solutions at room temperature [17] may represent a peculiar case of a conformational transition driven by the opportunity to form a liquid crystalline phase. 

Hamaguchi, M., and K. Yoshino. 1994. Lyotropic behavior of poly(2,5-dinonyloxy-p-phenylenevi-nylene). Jpn J Appl Phys 33 L1478. 

Tetracarboxyphthalocyaninatocopper forms lyotropic phases in aqueous solution [162] as long as Li or Na are present as counterions [163]. From the investigated phthalocyanines nevertheless only the copper complex shows this lyotropic behavior. Likewise, the liquid crystalline characteristics disappear by substituting the carboxylate groups with sulfo groups [163]. 

Amphiphilic behavior is related to conducting polymers and to mesomorphic polymers for several reasons. First, doping of PANi with surfactant molecules has been found to induce liquid crystallinity. Second, alkylation of semiflexible conducting polymers (PT and PANi) favors the formation of layered structures. Third, both rigid and flexible macromolecules with alkyl side chains may be considered as diphilic, in which case lyotropic behavior is to be expected. In the next section examples of mesomorphism and structural organization for macromolecules with flexible side groups will be given. 

Cylindrical Morphology. Fredrickson [32] studied surfactant-induced lyotropic behavior in polymer solutions. If the degree of polymerization of the backbone is N, the number of surfactant molecules is ctN, where a is a dimensionless parameter defined as the number of surfactant molecules per monomer unit. If the degree of polymerization of the surfactant is M, the Flory radius for surfactant molecules is... 

The lyotropic behavior of ethyl cellulose in various solvents (methanol, ethanol, diox-ane, acetic acid, acetic anhydride, m-cresol, phenol, etc.) was studied as a function of the critical concentration of the liquid crystal phenomenon produced by refractometry, polarized light microscopy, and optical transmission [118, 119]. It has been observed that critical concentration increases with decreasing the solubility of the solvent, and also that the critical concentrations for alcohols were much higher than those of other solvents with similar solubility parameters. 

A few alternatives for the derivatization of cellulose have been found recently direct dissolution of cellulose has been developed. For textile filament yams, dissolution in N-methylmorpholine oxide (NMMO) is possible. The process is applied by Courtaulds and Lenzing. A solution in formic acid/phosphoric acid was found to have lyotropic behavior and tire yarns with very interesting properties could be produced (patented by Michelin). It even proved possible to use phosphoric acid alone (patented by AKZO), but the process was never commercialized. 

Aramid yarns (Kevlar of DuPont, Twaron of Teijin-Twaron) are produced from poly(p-phenylene terephthalamide), PPTA (2), which is specially developed for fiber spinning and not used in any other application. DuPont had experience with poly(m-phenylene isophthalamide) in a fiber product called Nomex for high-temperature applications. The polymer is produced in dimethylacetamide and the solution is dry-spun. This cannot be done with the stiff-chain para-para analogue PPTA. The polymer does not dissolve in organic solvents. A special polymerization route had to be developed, and the discovery of lyotropic behavior of concentrated solutions in sulfuric acid then led the way to the production of a magnificent new fiber material. 

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